Training Deer to Eat MORE Japanese Knotweed

This post represents a first for PrincetonNatureNotes.org, in that it is written by someone other than me. Mark Nowotarski lives in Stamford, CT, and contacted me more than a year ago after discovering a 2014 post I had written entitled Training Deer to Eat Invasives. Independently, he had begun foraging the Japanese knotweed growing in his backyard (young shoots are edible) and noticed that deer began browsing it as well. Released from any co-evolved limits on its growth, Japanese knotweed has spread across the US and globally, displacing native species and overwhelming any human efforts to counter it. Unlike people, deer are 24/7 land managers. Their appetites decide what can and cannot grow in our yards and woodlands. Training deer to eat a relatively edible species like Japanese knotweed could conceivably, in some situations, relieve browsing pressure on the native plant species deer tend to prefer. As the deer in Mark's backyard continued to consume young sprouts of Japanese knotweed, he sent me photos and text that I incorporated into a post a year ago.

This past growing season, Mark expanded his experiments and observations, exploring how a willingness to browse Japanese knotweed could pass from one generation of deer to another. It's still unclear how much of an impact deer browsing could have on the spread of Japanese knotweed, but it's an interesting inquiry. Along the way, we learn about deer family dynamics, the potential grazability of another uber-invasive, porcelainberry, and even the possibility that deer saliva affects the chemistry of plants. Thanks to Mark for sharing his work with us.

Training Deer to Eat MORE Japanese Knotweed

By Mark Nowotarski

In our post last year, “Training Deer to Eat Invasive Plants – Japanese Knotweed”, I shared observations of white tailed deer (Odocoileus virginianus) browsing a patch of Japanese knotweed (Reynoutria japonica) in my backyard in Stamford CT. The local deer had learned to browse the knotweed continuously from spring to fall resulting in drastically stunted canes. This had allowed numerous native plants to recolonize what had previously been an invasive monoculture. Steve and I speculated that perhaps if we cut the fully mature canes in other nearby patches of knotweed (i.e., coppicing), new shoots would grow and the deer local to those patches might browse the new shoots as well. I’m happy to report that that strategy at least partially worked.

Deer Raising Fawns on Knotweed

Before we talk about manual coppicing, let’s talk about how it’s occurring naturally. This first video, shot in May in my backyard, shows you what deer browsing spring knotweed shoots looks like.

A buck with new antlers approaches several knotweed shoots (Fig. 1). He gives a quick sniff, bites the top portions off, and eats them. The cut stems that are left behind are about 2 feet tall.

This particular buck may well be one of the fawns raised on knotweed in my backyard in the prior summer of 2024. Does and fawns form a family group when the fawns are born in late spring. They normally stay together and browse in the doe’s home range for a full year before dispersing shortly before the doe, if she’s pregnant, gives birth to the next year’s fawns. This is how last year’s fawns learn to eat the new shoots of knotweed that sprout in the early spring. The early spring browsing by last year’s fawns coppices the knotweed so that when it sends out new shoots at a convenient two foot height, the new shoots will be available for the new fawns born in late spring.

This year, our doe was, in fact, pregnant and sometime in June, she gave birth to triplets. Triplets are relatively rare (1 in 10 pregnancies) and indicate that the doe is well fed. By July, the doe and the new set of fawns were out browsing the knotweed previously coppiced by last year’s fawns before they dispersed.

In the foreground of Fig. 2 you can also see several native plants growing up through the coppiced knotweed. On the left is Canadian goldenrod (Solidago canadensis). On the right is Northern lady fern (Athyrium angustum) and sensitive fern (Onoclea sensibilis). The deer would occasionally take a nibble of the natives, but they concentrated primarily on the knotweed. 

This suggests that some of the native species less appealing to deer could begin to coexist with browsed stands of knotweed. I plan on trying this strategy next summer and will keep you posted.

I had set up a motion activated trail-cam to monitor how often, and for how long, the doe and fawns browsed the knotweed over the summer. They returned 4-5 times a week and browsed 5-15 minutes for each visit. This lasted from when I set the camera up in July all the way through late October when the knotweed senesced (i.e., dropped leaves and turned brown). So far this winter, the doe and fawns are still stopping by several times a week. In late October an 8-point buck also stopped by in the middle of the night. After a bit of hide-and-seek with the doe in the knotweed, they mated. We can now hopefully look forward to new fawns this spring.

The cycle of fawns being raised on knotweed and then dispersing in the late spring to new territories may be an important mechanism for the spread of knotweed browsing by deer. The question then becomes, can we spread it even further by coppicing canes ourselves.

Expanding Knotweed Browse with Manual Coppicing

At the same time I was monitoring the deer in my backyard I also set out this past year to explore the knotweed stands in our local parks and land trust sites to see if I could find additional evidence of deer browse. About half of the stands I inspected showed signs of early spring browsing. About half of the spring-browsed sites also showed continued summer browsing. Several of the summer-browsed sites showed a significant expansion of the browsed area versus last year. This was evidenced by areas with tall old canes from last year but only shortened canes this year. The deer hadn’t eaten the knotweed last year and it grew to full height. This year, however, they started in the spring and continued through the summer and fall keeping it short.

To try out the manual coppicing experiment, I selected four sites where there was either no early spring browsing or where there was some spring browsing but no rebrowsing of the new shoots emerging from the coppiced canes. Two of the sites did not show any rebrowsing of the coppiced canes. These sites either had no spring browsing or very scattered spring browsing. The knotweed threw out new shoots which grew to full height despite clear evidence (e.g. footprints) of deer wandering by. Apparently, the deer near those stands had not been sufficiently acclimated to knotweed as a source of food.

In the other two sites, however, the deer did resume browsing the new shoots thrown out by the coppiced canes. These sites had heavy spring browsing and well-worn deer trails right next to the knotweed stands.

The next set of figures shows the history of my coppicing experiment at one of the sites where the deer resumed browsing. 

Fig. 3 is a photo taken in April. It shows what an early spring browsed knotweed shoot looks like. It also shows a new shoot emerging from the cane a few weeks after the initial browse.

Unlike my backyard, however, these new shoots were not rebrowsed. By July they had grown to full height. This, along with the well worn deer trail right next to the knotweed stand, made it an ideal location for the coppicing experiment.

The next photo (Fig. 4) shows a section of the knotweed stand where I cut a 6 foot wide by 12 foot long section of the full grown knotweed canes to about 2 feet off of the ground. 

I cut the canes at a bias so that when I inspected them later on, I could tell whether a cut cane was my doing (angle cut) or a deer browse (horizontal cut). Cuttings were placed where they could not resprout or be washed downstream.

A few weeks later I went back to inspect and, much to my delight, the deer were browsing the new shoots emerging from the manually coppiced canes (Fig. 5). 

Where I had cut the canes, the ends were frayed and the canes turned black down to the next joint. Where the deer browsed the canes, however, the ends appeared to be sealed off and even flared out as if from accumulated water pressure coming up through the knotweed. The canes below the deer browse remained green. It makes me wonder if there is something in the deer saliva that causes a deer browse wound to heal quickly. Perhaps knotweed has evolved this way from browsing by sika deer (Cervus nippon) in their home range in Japan.

Once I confirmed rebrowsing of the new knotweed shoots at this particular site, I set up another trail cam to see what sort of deer were coming by. I half expected another family of a doe teaching fawns to eat knotweed.

 

Imagine my surprise when this magnificent 14-point buck showed up (Fig. 6). It wasn’t a family group. It was a bachelor group with up to four bucks coming through at various times.

This buck and several others came by 4-5 times a week to browse not only the knotweed, but the invasive porcelain berry (Ampelopsis glandulosa) growing over the area in the foreground and hanging off of the uncoppiced knotweed canes in the background. In fact, I suspect that the porcelain berry is the primary reason the deer were there. The knotweed was just an additional food source.

The bucks suddenly disappeared in mid-September after they shed their velvet, no doubt to pursue does during the rutting season. I have not seen them since except for one poor fellow with a missing antler. Given how well-worn the deer trail is, however, I expect to see at least some of them again in the early spring.

Deer in a given area learning to eat Japanese knotweed appears to be a multi-year process. It starts with initial occasional browsing of early spring shoots. The spring shoots are then browsed more intensely in the ensuing years. Eventually the deer start browsing the new shoots growing from the spring browsed canes. If the knotweed is in a doe’s home range, then she starts to raise her young on knotweed and then the process spreads as the fawns raised on knotweed go on to establish their own home ranges.

If you try your own coppicing experiments, please let us know how they work out. I’ve joined a project on iNaturalist called “North American Knotweed Ecology Project” where we can share our observations. iNaturalist is a great tool for finding knotweed stands in your area. If you look carefully in the knotweed photos, particularly those taken in April and May, you can often see a deer-browsed shoot here and there. Sites with browsed shoots would be a likely candidates for coppicing experiments.

In the future I hope to learn more about the general phenomenon of deer adjusting their diets to consume invasive plants; how this affects browsing pressure on native plants; and what impact it might have on the deer themselves. The deer won’t solve all of the problems with invasives, but they may very well be an important part of the solutions.

- Mark Nowotarski

Editor's note: A related initiative is the effort to train cattle to eat invasive species. A woman named Kathy Voth appears to be a leader of this approach. 

Playing the Healer of Nature

One of PrincetonNatureNotes' sister blogs is FOHWard.org, specific to our work and play at Herrontown Woods, the fabled preserve that our nonprofit Friends of Herrontown Woods takes care of. Posts range from the celebratory to the comic, as in when we intervened to scuttle an attempted "theft" of a portapotty. 

For those who imagine cutting invasive species to be dull work, a recent post on that blog, Stewardship and Discovery at Herrontown Woods, might be of particular interest. It captures how elements of beauty, effort, strategy,  serendipity, and discovery can come together to make a stewardship session a rich and satisfying experience. 

Cutting nonnative invasive shrubs, we are essentially deer with loppers. Deer move through the forest looking for something edible to browse. They generally leave the nonnative shrubs uneaten, and so to prevent those nonnative, inedible shrubs from taking over, we move through the forest with our loppers with an eye for "browsing" the nonnatives, to balance out the deer's persistently lopsided appetites. Unlike deer, we aren't in the woods 24/7, and so to have a lasting effect it's necessary to treat the cut stem so it won't grow back. By releasing native plants from competitive pressure, over time we make the forest more edible for deer and other wildlife, essentially expanding the acreage of functional habitat in Princeton. 

Some would say that humans are an invasive species, so who are we to presume we can make a positive difference. But if we can be considered invasive, we are also equipped to play the role of stewards, to see the consequences of our invasiveness and act to heal the altered earth. As we move deer-like through the forest, our appetite is not an extractive search for food but for restoring balance. To abdicate on that role would be to deny what it means to be human.

I don't know if deer can appreciate beauty or serendipity as they browse, but we can. In Herrontown Woods in autumn, each leaf reveals its inner color. Each boulder is a work of nature's art, mottled with varied shapes of lichen and moss, like the mottled skin of whales navigating the oceans. To steward a preserve is, of course, a considerable task and responsibility, but in another way, working with nature is a great privilege, allowing us to realize our highest role, as stewards, appreciators, and healers of nature's creations.

The Mystery Tree Found in Autumn Hill Reservation

Not everyone gets to discover and report on a new invasive species in one's adopted home town. Though there were a couple kinds of invasive plants that I caught early enough to hopefully keep from spreading through town--thorny mile-a-minute and more recently the dreaded common buckthorn--this particular discovery is different, in that people have yet to agree on what it is. How strange it can feel, in a time when the internet can instantly tell you everything about everything, to find a plant to which no one can with certainty give a name.

I first encountered a single specimen of the mystery tree while conducting a plant inventory in Roger's Refuge in 2007. Only in the past few years have I found it proliferating in Herrontown Woods and Autumn Hill Reservation. 

Some call it a shrub, though when it grows to 30 feet, maybe it's time we start calling it a tree. There's agreement that it is in the genus Pourthiaea--a name that people will struggle to spell and pronounce (my attempt at a pronunciation is "pore-THEE-uh"). In a discussion on iNaturalist, the citizen science site for reporting and identifying species, some try to call it asian photinia (Pourthiaea villosa)--a nonnative shrub that likely escaped from Princeton-based nurseries long ago.

They are surely wrong, as the leaf shape and fall color of asian photinia are clearly distinct. This bright golden yellow is increasingly prettifying and clogging Princeton's greenspaces, from the Institute Woods in the west to Autumn Hill in the east, creating dense, exclusionary stands as it spreads beyond Princeton to proliferate across New Jersey. 

John L. Clark, a Princeton-based botanist frequently posting on instagram from the forests of Equador, has done a great deal of research into our mystery tree. Since the Pourthiaea genus originated in China, John tracked down a couple Chinese botanists to seek their insights. 

One, D.Y. Hong, responded that he was too old to take on the challenge of identifying the tree.

Another, Bin-Bin Liu, was also apparently unable to assist. John laments that botanists now trained in phylogenomics can identify gene sequences but not the actual physical plants themselves. 

There have been various species names thrown at the mystery tree--lurida, lucida, arguta--but none clearly stick thus far. Through Mike Van Clef, I learned of Jean Epiphan, a northern NJ plant expert at Rutgers, who had arrived at the species name "parvifolia", and even came up with a common name, "littleleaf photinia." Originally introduced in 1908 at the Arnold Arboretum," it's popping up in Morris County and, according to Jean, matches our mystery tree in Princeton. She has not seen it being sold in nurseries, and speculates that it is spreading from specimens in old estates. She sent a couple links (here and here) with descriptions, and a mention of it in Dirr's encyclopedic Manual of Landscape Plants.

Some sticking points, though, are that the link she sent to a photo has now gone dead, and the description is of a shrub less than ten feet high. A photo sent by Pat Coleman from Bowman's Hill Wildflower Preserve also matched our mystery tree in Princeton, but no word as yet whether they've come up with a name.

One thing to call the mystery tree is pretty, as are many invasive shrubs, both when they bloom and in the fall. This fall in particular, Autumn Hill Reservation was a jubilant jumble of colorful invasive shrubs, led by the bright red of winged euonymus, joined by the rich colorations of Linden viburnum and the golden yellows of the asian photinia Even the lowly privet got into the color game with an appealing dark bronze. 

When surrounded by such a dazzling visual display, it takes work to remind oneself that something important is being lost as these introduced species gain dominance in the understory. Their success and dominance is enabled in part through being rejected by deer, which prefer a diet of native plants. Thus, our eyes are well fed while the wildlife find themselves living in an increasingly inedible forest. 

As we lose many of the native trees dominating the canopy--chestnut, elm, ash, and now the beloved beech--the extra light reaching the understory drives the extravagant growth of nonnative shrubs. Surrounded by such a thorough invasion of nonnative growth, it is extraordinarily intimidating to contemplate the work involved to shift the balance back to the spicebush, blackhaw viburnums, blueberries, hollies, sumacs, and other natives currently getting smothered beneath the rising tide.

Native shrubs and trees don't exactly lack color. Here's a dogwood that was mixed in and easily confused with the mystery invasive. Note the way the leaves are paired rather than arising one at a time along the stem. 

All the invasive shrubs currently dominating were at one time, long ago, in a similar state, just starting to pop up here and there. Clearly there was no one back then able to see the future and take early action. In our era, the consequences of inaction are readily apparent. What is special about this moment in the history of Autumn Hill Reservation is that the mystery tree is still early enough in its invasion, and easy enough to spot in fall, that it can be stopped.  

Update:

Where found thus far:

• Rogers Refuge, Herrontown Woods, and Autumn Hill in Princeton
• Possible sighting in the Institute Woods in Princeton
• Bowman's Hill Wildflower Preserve
• Jockey Hollow and the NJ Brigade Area in Morris County
• Tourne Park, in Boonton

Update: A big thank you to "anonymous" in the comment section, who provided a species name and links to herbarium photos:

"Thanks for alerting us to this newly naturalized species. One of the best resources for documentation of plants on a global scale is GBIF. Reviewing the gallery of specimens online, the name leaves to appear to bear a resemblance to Photinia parviflora. https://www.gbif.org/occurrence/gallery?taxon_key=5363981"

Each photo at the link bears the name C.K. Schneid. Look at the wikipedia page for Camillo Karl Schneider and you'll find that he was a German botanist who traveled to China in 1913 to collect plants and seeds. His next stop was the Arnold Arboretum in Boston, where the species is said to have been introduced five years earlier by Wilson in 1908.

Each photo shows that the now accepted species name is not parvifolia but instead parviflora. 

Applied name Photinia parvifolia (Pritz.) C.K.Schneid.
Accepted name Pourthiaea parviflora (Cardot) Iketani & H.Ohashi

That puts into question the common name "little leaf photinia", since "parviflora" means little flower. 

So, we're not really there yet. 

Buckthorn--A New Highly Invasive Shrub Found in Princeton

For years, I've traveled between Michigan and New Jersey and noted how some invasive plant species that have run rampant in the eastern U.S. have yet to show up in the midwest. That is changing. Last year, I encountered a dramatic example of stiltgrass spreading down a hillside in Michigan, and there are reports of lesser celandine gaining a foothold there as well. Similarly, Princeton had remained free of the common buckthorn--the most invasive shrub clogging midwestern forests. That, too, is changing.

The fateful day came on September 16, 2025. I was standing in a spot I'd passed by many times, near the entrance to the Herrontown Woods parking lot, when I happened to look down and saw that characteristic leaf of common buckthorn--the first sighting, by me and perhaps anyone, of this uber-invasive shrub in Princeton. 

The leaves of common buckthorn (Rhamnus cathartica) have arc-shaped veins, and are described as "sub-opposite," because they can appear to be paired on the twig but are slightly staggered.

Buckthorn gets its name from the two terminal buds, which make the shape of a buck's hoof, with a thorn-like protrusion between them.

This photo from upstate NY shows there can be thornlike protrusions along the trunk as well.

Shunned by deer, buckthorn's combination of massive seed production and shade tolerance allow it to clog forests and bury whole native plant communities under its dense growth. The richly diverse bur oak savannas of the midwest were nearly lost beneath a rising sea of buckthorn. Only botanical sleuthing and the hard work of clearing buckthorn, honeysuckle and other invasive plants from beneath the massive oaks, along with reseeding and prescribed burning, has brought back that plant community. 

The small cluster of young shrubs I spotted at Herrontown Woods has fortunately not yet produced seeds. But anyone who has lived in the midwest knows the potential of buckthorn to grow, seed and spread.

An email to the Stewardship Roundtable group of land managers in NJ yielded some responses. Duke Farms has it, as does the Watchung Reservation. The Friends of Great Swamp have an info sheet on their website, so I suspect it has established itself there as well. Mike van Clef, who deals with invasive plants all across New Jersey, writes: 

Duke Farms definitely stands out! From iNaturalist, there are 64 research grade observations, heavier toward northern NJ but all over the state. I often find it as single immature individuals, especially in northern NJ...which is always a head scratcher because I never seem to find a nearby large fruiting individual...

This photo shows the lingering green of buckthorn in upstate NY. Like many invasive shrubs that evolved in a different climate, buckthorn keeps its leaves longer that native species in the fall. 

Given New Jersey's already long list of invasive shrubs clogging our forests--among them multiflora rose, Photinia, privet, and Linden Viburnum--it's hard to imagine another having much of an impact. Having seen what buckthorn does in other areas of the country, all I can say is "Watch out!"

Early detection and rapid response are key to stopping biological invasions. This is true both of the immune systems protecting our bodies and of land managers caring for nature preserves. At Herrontown Woods, we've done very well with that creed of early detection and rapid response. Lesser celandine and garlic mustard--the bane of many a nature preserve--are now vanishingly rare. Vigilance each year in August has helped keep many areas free of stiltgrass, the most rapid spreading of all. People who care and take action can make a difference.

On a town-wide scale, some early interventions have helped keep the thorny Mile a Minute vine from spreading across Princeton. Though Princeton has hired contractors to help counter at least some invasions in their early stages, it's hard to get private residents--often disconnected from the yards they own--to act collectively to knock out new invasive species before they become a problem. Having fought the good fight, my advice about buckthorn is: be informed, be on the look out, and be proactive. There's also a super handy, targeted, and frugal way for homeowners and professionals to cut and treat buckthorn and other invasive shrubs. Appropriately enough, it's called a Buckthorn Blaster. 

Fuel Tank Raingarden, Lost to Weeds, Receives Reboot

Well, it finally happened. After five years of letting weeds get the upper hand, a maintenance crew declared defeat and tore most everything out of the raingarden next to the town fuel tank on Witherspoon Street. 

The trajectory from first year splendor to decline and fall (see links below) is a familiar one. For thirty years, in three different towns and cities, I've been watching how complex landscape plantings prosper or decline. By complex, I mean any planting containing more than three intended species.

One could talk about how maintenance is undervalued in our society. People talk about planting a tree, but few talk about the followup care--the watering and weeding that determine whether that tree survives. Good maintenance is invisible. People notice when things go wrong, not when things are kept right. This is true whether it be a well maintained raingarden or a well-run government. Both go underappreciated, at their peril. 

And we could talk about pervasive plant blindness--the scarcity of people who can distinguish one plant from another. We expect medical staff to be knowledgeable about the human body and its afflictions. A raingarden also requires expertise to keep it healthy. To weed with confidence, the landscape crew needs to be able to identify not only the intended plants but also the myriad weeds that invariably move in.

Here, in the foreground of this photo, you can see the main culprit. Though there are many other weeds, mugwort is the most aggressive non-native weed in a raingarden. Unchecked, it spreads quickly, soon leading to a sense of despair. 

Also working against success is the typical scheduling used in a maintenance department. What if the two visits per year coincide with dry conditions? Weeding is best done when the ground has been softened by rain, and before the weeds have a chance to set seed. For a raingarden to be low-maintenance, intervention needs to be strategic and well-timed. That won't happen with a rigid schedule. 

And sometimes I wonder, in this era of toxic masculinity when empathy is criticized as a weakness, whether a raingarden for some is too feminine, too complex or too hippie-like, and so ultimately yields to the masculine need to dominate with a mowing machine rather than nurture with a trowel. For whatever reason, the simplified, close-groomed look of a lawn tends to win out.

Turns out, though, that the fuel tank raingarden wasn't converted to turf out of frustration, but was instead replanted, probably at considerable cost. This suggests a commitment to maintaining the raingarden as a garden.

And yet, at the bottom of this photo, you can see the mugwort has not completely gone away. 

Like our own immune systems, constantly quelling potential riots of pathogens lurking inside our bodies, a raingarden needs someone skilled in quelling the quiet riot of weeds lurking in the soil. With vigilance and timely intervention, the job gets easier and easier and the raingarden will flourish as originally intended. A skilled caretaker would spot these weeds and pull them out before they have a chance to gain momentum.

 

Just for comparison and to show what's possible, here is a thriving raingarden in Hopewell, in front of the Peasant Grill. It remains a low-maintenance, attractive planting year after year, surely because someone with knowledge acts quickly to pull weeds before they can get established. This is the informed, timely intervention we expect for ourselves in good medical care.

But even in that well-tended planting in Hopewell, a few pesky mugwort are ready to become many if there's no skilled caretaker to spot them quickly and pull them out. Sustaining peace, beauty, and harmony requires ongoing vigilance.

Another example is the wet meadow I take care of at Smoyer Park--essentially a detention basin planted with native wildflowers and grasses. It is fed by runoff from the main parking lot.

Below are annual posts that have tracked the fate of the fuel tank raingarden, from bare ground to freshly planted splendor, followed by increasingly weedy chaos and this year's reboot. 

2020 Princeton Fuel Tank Raingarden Wannabe

2021 Princeton Finally Plants its Fuel Tank Raingarden

2022 Weeding Princeton's Fuel Tank Raingarden

2023 Fuel Tank Raingarden Threatened by Lack of Early Intervention

2024 Fuel Tank Raingarden Losing Out to Weeds

Training Deer to Eat Invasive Plants -- Japanese Knotweed

Here's a story and a partially forgotten concept from ten years ago that a commenter on this blog helped me reconnect with. The concept has to do with actively training deer to eat invasive plants. Thanks to Mark Nowotarski of Stamford, CT for reminding me of this concept, and adding his own interesting twist.

Deer manage our landscapes with their appetites. Whether it's your unfenced yard or the local nature preserve, deer largely decide what can grow and what gets eaten down. Introduced plant species can become invasive if they are left uneaten by finicky deer, thus allowing them to proliferate rapidly and overwhelm native flora. Wouldn't it be great if we could train deer to eat invasive species, and thus restore balance to the landscape? 

Ten years ago, I wrote about two ways to potentially train deer to eat invasive species. One is to cut down invasive shrubs along the deer paths and let the stumps resprout, thus presenting the deer with tender new shoots to nibble on. As the deer (hopefully) grow accustomed to the taste and texture of the invasive's new growth, perhaps they would begin eating older foliage as well. 

It's also possible that the deer respond to visual cues. If we repeatedly cut back an invasive shrub, deer may assume other deer have been eating it, and chow down. Deer have reason to revisit a shrub again and again. By eating its foliage, they stimulate the shrub to replace the lost leaves with new ones, much as we do with basil and other vegetables in our gardens. Making their accustomed rounds, deer essentially farm the forest for fresh foliage.

Though we experimented with this at Herrontown Woods mostly with winged euonymus, Mark reports some success with recruiting deer to browse a patch of Japanese knotweed in his backyard:

"I've seen a similar phenomenon where I live in Stamford CT. We have a little bit of woods in the back yard where deer tend to congregate. There is a dense stand of Japanese knotweed down by a small stream. A few years ago, I started foraging the tips of the knotweed in the spring and noticed that the deer continued to browse the knotweed through the summer. Every time the knotweed would send out new shoots, the deer would browse the tips. At first they just browsed where I foraged, but in the past few years now they have expanded the browsed area and are actually beating back the knotweed. If you see any knotweed browsing in your area, I'd love to hear about it."

He sent photos and more text to illustrate:

"About 4 years ago, I noticed that the deer on our property had started browsing the spring shoots of a stand of Japanese knotweed. The knotweed grows down by a swampy stream and has been there for at least 30 years. Each year the deer have browsed the stand more intensely." 

"When the knotweed throws out side shoots after the initial browsing, the deer browse the tips of the side shoots. When the side shoots throw out secondary side shoots, the deer browse the tips of those as well. This continues through the summer."

"The knotweed in the browsed area is kept to about 3 feet tall and is very sparse. Abundant sunlight falls on the forest floor and there has been a substantial increase in the plant biodiversity of the browsed areas." 

"This includes the sprouting of native plants, such as Sassafras albidum (Sassafras) and Impatiens capensis (Jewel weed). I found the I. capensis particularly surprising since this is normally heavily browsed by the deer."

"The deer only browse a portion of the knotweed stand. If a knotweed shoot reaches full size, it’s not browsed. Nonetheless, each year the deer have been browsing a larger and larger area. They originally browsed just an outside edge of the stand where I used to forage knotweed shoots in the spring, but last year they started hollowing out the center of the stand." 

"Based on your experience with winged Euonymus, this leads me to suspect that it might have been my initial foraging that led the deer to continue the browsing. It would be interesting to forage some unbrowsed knotweed in the spring and see if the local deer continue."

Thanks again to Mark Nowotarski for these photos and descriptive text of the interesting dynamic between deer and the patch of invasive Japanese knotweed in his backyard. In our experiment ten years ago with winged euonymus, we found that invasive shrubs ultimately grew back, likely due to our having cut so many that their myriad young shoots overwhelmed the deer's mild interest in their foliage. We also didn't think to try focusing our cutting close to deer paths. 

Anyone managing a sizable nature preserve will soon grow weary of cutting invasive shrubs only to have them grow back. Treating a freshly cut stem with a thin film of systemic herbicide, using a Buckthorn Blaster, is a targeted, minimalist way of actually making progress in a woodland choked with invasive species. 

But especially for the vast majority of woodlands that go unmanaged, the concept of training deer to eat invasive species has appeal. I'm looking forward to harvesting some young shoots of Japanese knotweed this spring, as an experiment. Having trained the deer in his backyard to eat this highly invasive plant, Mark may train me to eat it as well. Testimonials like this one suggest the young shoots are quite tasty. Research the how, what, where and when before giving it a try. Mark recommends sauteing with butter.

Update 1.30.25: Just came across another of my posts from ten years back, entitled Paradox Lost, or, Less Irony in the Woodland Diet, offering a third way to get deer to eat invasive plants. If there are mint-flavored sprays that discourage deer from eating ornamental plantings, maybe there's a flavor of spray that would encourage them to eat invasive plants. 

Stiltgrass Reaches Michigan

During four weeks of touring with our latin/jazz group Lunar Octet in California and Michigan this summer, this "jazz naturalist" kept encountering different variations on the problem of invasive species. In the Bay area of California, highly combustible introduced grasses dominate hillsides, threatening homes. A side trip to Cleveland took me close to where beech leaf disease was first identified 12 years ago. 

And then, housesitting for my friend Sam in Ann Arbor--our home base for various Michigan gigs--I was astonished to find Japanese stiltgrass growing in his garden. Now, the only thing that would be astonishing about stiltgrass in a New Jersey garden would be its absence. Stiltgrass has become nearly ubiquitous in Princeton--coating roadsides, establishing broad monocultural meadows in our woodlands, smothering our gardens with its stilt-like growth. An annual that spreads rapidly for lack of any wildlife that find it palatable, it dies back in the fall, leaving a frozen ocean of brown in the forest, and billions of seeds to sprout the next spring. 

Stiltgrass is Not Yet Everywhere

That ubiquity makes it hard to believe that there are still many parts of the U.S. where stiltgrass has yet to spread. Until recently, though, Michigan was one of them. For a New Jersey gardener, traveling to Ann Arbor used to be like stepping thirty years back in time to a stiltgrass-free landscape. 

My fantasy, upon discovering this uber-invasive in Sam's yard, was that I had through uncanny serendipity happened upon the first colony of the plant in the area, and at a time of year when it could be pulled before it went to seed. What finer gift could a housesitter give to a homeowner and his neighbors than to nip an invasion of stiltgrass in the bud? This jazz cat was going to put a botanical bully back in the bag. 

The Horse, the Cat, the Barn and the Bag

But no. The stiltgrass--which I'm guessing first arrived as a hitch-hiker in topsoil or a nursery plant, or perhaps in the soil of a well-intended gift plant dug from some well-meaning friend's garden--had already spread far down the hillside towards the Huron River. 

Turned out Sam already knew about stiltgrass. Ann Arborites are a plant-savvy bunch. Their city already had a Natural Lands Manager, Dave Borneman, long before I moved away in 1995. Princeton hired its first Open Space Manager in 2021. Most towns and cities don't even have one.

I contacted Dave, who now has his own habitat restoration business doing prescribed burns, to ask about the status of stiltgrass in Ann Arbor. He didn't say the cat was out of the bag, but he did say the horse had left the barn. "Sadly, the horse has left the barn on this species locally. We’re seeing it pop up fairly widely now in eastern Scio and western/northern AA."

The first occurrence of stiltgrass was in fact reported seven years ago, on Sept 1, 2017, in an announcement by the state Dept. of Natural Resources. A collaboration between the DNR and a nonprofit called The Stewardship Network sought to identify and knock out the initial population, said to have been limited to one property, but to no avail. 

The First Sighting in Wisconsin 

Wisconsin's situation sounds more hopeful, with only one known infestation that is allegedly being managed and kept to a limited area. A botanist visiting from Minnesota made the early identification. Somewhat less reassuring is a post by the Invasive Plant Association of Wisconsin (IPAW), that mentions my childhood landscape in the Lake Geneva area specifically as a place where people should be "on high alert" for stiltgrass. That would suggest its been reported there.

Is Stiltgrass Controllable?

It got me thinking about what can a town do about a new invasion? Once the cat has left the barn and the horse is out of the bag, is there anything to be done? Ann Arbor certainly needs no advice from afar. Its Wild Ones chapter has an excellent fact sheet on stiltgrass in Michigan, including a field guide with details to help with distinguishing stiltgrass from some similar-looking native grasses like whitegrass. Other groups like the Legacy Land Conservancy are also engaged, sounding the warning that Michigan gardeners and land stewards now face a challenge like no other.

“Stiltgrass is not like other invasives we have seen in Michigan, which spread relatively slowly and can be contained. Stiltgrass travels via water and deer, as easily as water itself."

But Princeton's experience with uber-invasives like stiltgrass and lesser celandine can be instructive. One can say these rapidly spreading nonnative species are ubiquitous, and yet there are locales--backyards, neighborhoods, upper valleys, hillsides--within the town where one or another invasive has yet to spread. In the preserves I have managed, I have had considerable success with proactive action to keep various areas free of the lesser celandine, garlic mustard, and porcelainberry that plague other areas of Princeton. 

Much can be done to slow the expansion of stiltgrass, by patrolling in late summer, particularly along the edges of trails. Even though stiltgrass has been in Princeton for many decades, it's still possible to walk through portions of preserves and see none, or to find just a few along the trail that can easily be plucked up before they go to seed in September.

One has to keep at it year after year, catch any invasion early, and be strategic in one's timing to maximize result and minimize effort. For larger patches that would be impossible to pull, late season mowing and/or application of very dilute herbicide prevents production of new seed. Doing this thoroughly and year after year ultimately exhausts the seedbank. Scroll down at this link for more information on these approaches. 

Patrolling for stiltgrass in a preserve can even be a good motivation to get out into areas you might not frequent otherwise, and do some botanizing. It's a chance to sharpen the eye, as one distinguishes between stiltgrass and the native whitegrass, and a few other plant species with similar appearance.

The top half of this photo is native perennial whitegrass. The bottom half is the invasive, annual stiltgrass. The latter is easy to pull. The former resists, because of its greater investment in roots.

In this list of lookalikes taken from the internet, the whitegrass and the northern shorthusk have been enjoyable for this plant geek to get to know a little better this year. As is typical of native species, they are fairly common in less historically altered preserves, but don't take over like stiltgrass tends to. 

Smartweeds (Polygonum spp.), with tiny, white to pink flowers on a short spike and a tell-tale dark blotch near the center of each leaf.
Whitegrass (Leersia virginica), which is well-rooted in the soil and has longer, thinner leaves than stiltgrass, with no mid-rib stripe.
Northern shorthusk (Brachyelytrum aristosum), with fine hairs on the top, bottom and edges of its leaves and stems, and leaf veins in a pattern resembling an irregular brick wall.

That's the upside of intervening in a situation where many feel frustration and helplessness. Intervention to stem the advance of hyper-aggressive plant species gets us outdoors, often prompting new discoveries and providing a chance to gain more familiarity with the native diversity we seek to protect.

Botanical Threats to Greenway Meadows--Neighbors Raise Concerns

Over the years I've sung the praises of Greenway Meadows, the park in western Princeton with an asphalt trail running down the middle of an expansive meadow. One post describes the beauty of broomsedge and cross country racers "testing inner nature in a natural setting." Another describes the exhilaration of riding a bike through the meadow on the way to an art exhibit opening at the Johnson Education Center.

More recent visits to Greenway Meadows have focused on the threats to the park posed by invasive species, and the need to act quickly, before the problem gets overwhelming. This past April, it was dramatic to see how lesser celandine is beginning to invade the meadow and the lawn.

Then this summer, Mimi Schwartz, who lives near Greenway Meadows, reached out about the park. She had noticed some attrition among trees along the Poetry Trail, and wondered if competition from the tangle of invasive shrubs growing beneath them might be a cause.

Another neighbor of the park, Jennifer Widner, is focusing on threats to the meadow--threats that surely go unnoticed by the many people who walk or jog down the asphalt trail, see a pleasing green, and look no closer.

Still apparent to all are the many native wildflowers in the field, among them common milkweed and wild bergamot. 

But on a visit to meet Jennifer, I was astonished to see the extent to which Sericea lespedeza (aka Chinese bushclover, Lespedeza cuneata) is beginning to dominate. This is an invasive species that has become a big problem in the southeast U.S. and the plains states, but was comfortingly rare in Princeton when I first moved here in 2003.

There are various species of native bushclover that can sometimes be found mingling with other wildflowers in a field, but Sericea lespedeza doesn't, as they say, "play well with others." It's behavior is more that of a bully.

In understanding the threat posed, it helps to have lived elsewhere in the country where Sericea lespedeza has had a longer track record of aggression. Living in Durham, North Carolina, near where the species was first introduced, in 1896, and is still widely used for erosion control despite many efforts to have it banned from seed mixes, I witnessed its capacity to displace native species. 

For those who say live and let live, and let it be, consider the ecological consequences if the meadow ultimately becomes a monoculture of an introduced plant with indigestible seeds and inedible foliage. Here's one fact sheet's description:

"Sericea contains a high concentration of tannic acid, which causes wild and domestic animals to avoid eating it, unless no other food is available. Animals then forage more intensely on native plants, which depletes the desirables and allows invasives to increase. Tannic acid leaches from sericea into surrounding soil, creating a toxic environment that prevents or slows the growth of other plants, giving it yet one more advantage."

Mimi and Jennifer have had some success engaging public officials on these threats, and the land managers at DR Greenway's headquarters nearby are potential allies. 

The project with the clearest solution is the freeing of trees from the invasive shrubs growing beneath. A greater challenge, requiring intervention and vigilance for years to come, will be stopping uber-invasives like lesser celandine and Sericea lespedeza. 

My experience, though, is that the work can get easier year to year, as steady effort makes the invasives less numerous. Down the road, or down the trail, as the threat recedes, those involved may get to experience that wonderful "walk in the park" feeling, where the botanical bullies have been sent packing, and require only a bit of ongoing vigilance and mild intervention to prevent their return.

For more information on Sericea lespedeza, try these: BlueRidge and Oklahoma State.

Related post:

Monocultures in the Making - 2013

Fuel Tank Raingarden Losing Out to Weeds

Maintenance is looked down upon and taken for granted in our culture. One reason for this is that, done well, maintenance is invisible. Our human tendency is to notice what is wrong, not what is kept right. At home, we are more likely to notice dirt and disarray than the cleanliness and order a housemate worked hard to achieve. 

In landscaping, the tendency is to fund and celebrate design and installation, then leave maintenance to the vicissitudes of chance, undertrained and undermotivated staff, and perennially strapped budgets. But even with the best designs, maintenance is what ultimately matters. Maintenance is destiny. 

Maintenance at its best is a form of love. In gardening, what we call maintenance is really more akin to the nurturance of parenting--an ongoing process of encouraging what is desired, and discouraging what is not. A garden can also be thought of as a playground. When maintenance is done right, plants that exhibit bullying behavior, like mugwort, don't get to play in the garden. 

Environmental groups encourage people to dig up some lawn and plant native wildflowers. These meadow plantings are characterized as low-maintenance, but that is true only if the weeds are caught early. Once the weeds get firmly established, maintenance becomes very difficult.

The only gardens I've seen flourish are those that are loved, like a child is loved. Love leads to knowledge and steady attention, and early intervention when things go wrong. 

Just off Witherspoon Street in Princeton there are contrasting examples of loved and unloved public gardens. 

The loved garden in this instance has almost no weeds--a standard few of us achieve. For years, near the entrance to the Community Pool, gardens around the Princeton Recreation Department offices were taken care of by "Vikki C. and Team PRD," as the sign proudly declares. That would be employee Vikki Caines. Vikki's glorious plantings expanded over the years well beyond the Rec. Dept. building. She retired in 2023, but when I asked her, she assured me that her gardens would continue to be well kept. 
 

By contrast, just down the street, past the Princeton First Aid and Rescue Squad, lies a rain garden that collects water from hard surfaces around the town's fuel storage tank. Regulations require that raingardens be dug and planted to collect and filter runoff from new paved areas. In a series of posts, I've tracked the destiny of this very public but largely unnoticed raingarden, whose extended limbo in 2020 ended with planting in 2021. But in gardening, as when a baby is born, the birth of a garden is not the end but rather just the beginning. In 2022, it was still full of color and easy to weed, but by 2023 the weeds were getting entrenched. 

I alerted town staff that the raingarden was losing out to the weeds, and was told that the municipality was weeding it once or twice a year, and was working "towards a system of regular maintenance, while balancing many, many other priorities."

This year, the original plantings are beginning to disappear beneath waves of mugwort, nutsedge, and other botanical bullies that don't play well with others--

weeds like foxtail grass, 

and wild lettuce--to name just a few of the species that maintenance crews would need to be able to recognize and remove. Note that the designer of a garden must know only the intended plants, while the maintainer, typically underpaid and underappreciated, must additionally know and recognize the many weeds that can invade.

This is the difference between loved and unloved gardens. Imagine a child being notified that a parent was "working towards a system of regular visits, while balancing many, many other priorities."

Now, a town's public works department does of course have many other priorities. Job one is to serve people, not gardens. But that being the case, the aim would be to keep the raingarden in the easy-to-maintain stage by catching the weeds early. Vigilance and early intervention--a form of love--save time. 

The only way Vikki Caines could maintain beautiful gardens while also doing her job in the recreation department was to stay on top of the weeding. 

Well-designed raingardens are easier than most gardens to maintain. The runoff they collect keeps the soil soft for easy weeding, and many native species of wildflowers and shrubs are adapted to flourish in the wet ground. Regulations can call for the digging and planting of raingardens, but the fate of the planting is left to chance. Weeds grow 24/7, while people are easily distracted. If the weeds take over, the ultimate response will be to mow it down and manage it as lawn. Nature's complexity, unloved, unnurtured, will once again be simplified and suppressed, the better to pursue other priorities.

Related posts: 

To Save a Raingarden, Know Your Weeds 

The Work Behind a Natural-Looking Meadow: Smoyer Park in Princeton