Weeding Princeton's Fuel Tank Raingarden

When neighbor's complained about the appearance of the fuel tank on Witherspoon Street, the town responded by removing the fueling station's roof, adding a brick facade, and planting the raingarden that had been built to catch and filter runoff from the pavement. 

With the raingarden looking good in its first full year, the intended plants tidily mulched and flourishing, you'd think that it's time to sit back and enjoy nature's beneficence.

But as a gardener who has seen many a raingarden succumb to weeds, I could not help but notice the first signs that a silent, weedy insurrection was in the works. Here is a small patch of mugwort, planning a rhizomatous takeover.

Here's another little, harmless-looking cluster of mugwort next to a lovely St Johnswort shrub. And what's that grasslike plant in the background? That would be nutsedge, easy to pull but also with an underground network of roots that is hard to exhaust. If allowed to grow, it too will spread everywhere. 

The weeds look harmless when there are just a few, but a gardener can extrapolate in the imagination from a little to a lot. I couldn't help myself, and intervened. How many gardens are at such an early stage when thirty minutes of weeding can nip invasion in the bud? Here are horse nettle, mugwort and nutsedge. Feel for the triangular stem on the nutsedge. "Sedges have edges."

Here is white clover, which is benign in a lawn but muddles things in a flower bed.

On the left is a vetch, not crown vetch thankfully, but still worth pulling. 

I pulled pretty much every weed except the nutsedge, whose takeover will hopefully be forestalled by the designated caretaker, if any. Afterwards, the raingarden looked to most eyes exactly like it had a half hour prior. The reward of proactive action is in imagining all the future work that has just been avoided. There will be more work, surely, but much less. 

Maybe someone with designated responsibility would have done the weeding anyway. Nice to think but hard to count on. 

Meanwhile, on the other side of the new fire station, another raingarden was planted at some point. Lots of good stuff growing, but much more intimidating in terms of weeds. It shows what happens when the weeds are allowed to gain a foothold.

The pink is crown vetch, an aggressive plant originally introduced to the U.S. to control roadside erosion. 

And then there's birdsfoot trefoil, originally introduced to the U.S. as nutritious forage for cattle.

And relentless bindweed growing up and over the native swamp milkweed. 

Subduing these three tough customers would take some major work, which makes it all the more amazing to be able to weed the other raingarden and feel like one has the upper hand. 

All of this leads to a point, or two, made before, that regulations require the planting of raingardens in the name of reduced flooding and increased water quality, yet maintenance operations are set up to handle only the simplest of landscapes--turf and trees. Raingardens are a complex community of plants, not a monoculture. They don't respond well to "mow, blow, and go." The person who cares for them needs to be more physician than custodian. They can be planted by people who don't really know the plants, but they need to be cared for by people who do, in a culture that devalues informed maintenance. 

When a Leaf Is Not a Leaf, and a Grass Is Not a Grass

The kids were having a gas, literally and figuratively, up at Hilltop Park last week when I went to lead a nature walk for Stone Hill Church's annual summercamp. Our Friends of Herrontown Woods nonprofit has been partnering now and then with Stone Hill Church, which borders Herrontown Woods up on Bunn Drive. Not easy to compete with bubbles on a summer's day, but even in a park that's mostly turf and trees, there's always some aspect of nature to point out. One of the counselors noticed large dragonflies cruising above the lawn, probably munching on tiny insects as the campers paused to eat their own snacks. I showed the campers how to identify a white pine (needles in clusters of five, just like the number of letters clustered in "white"), and how to tell that what looked like seven leaves on an ash tree was really only one compound leaf made up of seven leaflets. Tricky stuff.

A closer look at the ballfield revealed that what looked like grass wasn't necessarily grass. If you see light-green splotches in lawn this time of year, chances are you're looking at nutsedge, which looks grass-like but is actually a sedge. And how do you tell a sedge from a grass?

Pull one up, look at the stem and you'll see it's triangular. Roll the stem between your fingers and you'll see and feel that "sedges have edges"--the three edges of a triangle. Most sedges are native perennials typically found growing in wet ground, but the nutsedge is a nonnative that spreads quickly through gardens. Chances are, the kids could go home and find nutsedge invading their parents' garden. (see last photo in this post)

Another weedy plant flourishing in the ballfield was a round-leaved creeper named ground ivy or gill-over-the-ground.

Here's how it spreads, by sending out shoots above ground that make new plants. This weed too is common in gardens. If you want to prevent it from coating the ground, it's easier if you pull out the new extensions before their roots get too established. One could say its presence in the field is good news, in that it indicates that broadleaf herbicides aren't being sprayed on the grass.

Here's the typical look of nutsedge spreading through a garden. It lifts pretty yellowish seedheads to the sky while sabotaging the intended neat formality of a row of Liriope.

Later on, the campers got to appreciate nature in another way, sitting in the comforting shade of an ash tree while listening to a fireman talk about safety in the home.

Weeds that Launch an Underground Insurgency

More discussion of weeds here, after happening to see a great example of a particular category of weed--three different ones afflicting three gardens all in a row. It's important to know your weeds, because as soon as you find a plant that you like enough to put in your garden, there will be weeds ready to grow up it and over it and all around it. Catch them early and they won't be a problem.

A point that cannot be overstated is that a garden designer need only know the intended plants. A gardener--the one who gets dirty day to day realizing and maintaining some vision--must know not only the intended plants but all the other ones that pop up. To leave or to pull, that is the question. Being able to identify weeds empowers the gardener to take action. 

Many weeds will trick the inexperienced gardener. When first encountered, they may look pretty good, and seem pretty harmless, and so they get left to spread. Having gained advantage from our generosity, some of these deceptive weeds can become particularly tough customers, so that before you know it what could have been a small proactive pulling becomes a formidable task. 

 

Take this scene on Wiggins--one of my favorite streets because the houses are close to the street, encouraging gardening rather than a large, and largely useless, lawn. (Doesn't it seem like, starting with suburbanization in the 1950s, yards got bigger as people's knowledge of plants got smaller?) There are at least four of these gardens that caught my eye as I was riding by on my bike. One of the gardens is essentially weed-free, but I could see that the others, though they look okay right now, are each plagued by an underground insurgency.

Star of Bethlehem -- This first example of a weed's takeover will be least convincing for the reader. The white flowers of Star of Bethlehem set off the red tulips nicely. But despite its pretty name and pretty flowers, Star of Bethlehem's capacity to spread through a garden and pop up in the lawn (along with wild garlic, it springs up early in the spring to form something I call "lawn blotch") has made it less than loved. 

Bindweed -- Another garden has some standard ornamentals--iris, purple coneflowers--and what at first glance appears to be a nice groundcover. 

But that groundcover turns out to be bindweed. Firmly entrenched underground, it is just starting its quiet insurrection that will smother the garden as the season progresses.

Canada thistle -- One side of the third garden has been completely taken over by Canada thistle, which might better be called spreading thistle, since it's from Europe rather than Canada. Many a garden and field has been invaded by this plant. 

Here, for instance, is a garden where the landscapers spread that pretty black mulch that has become popular, but underground was a whole network of Canada thistle roots from which has sprung this year's crop. It will be impossible to garden this area.

Both bindweed and Canada thistle pull easily when the soil is moist, but that easy pulling is deceptive, as the underground root system remains undisturbed and ready to send up new shoots as soon as the gardener's attention turns elsewhere. A grasslike weed called nutsedge is also deceptively easy to pull. (Searching this blog for the word "nutsedge" pulls up some additional posts on weeds.)

Among the less common underground spreaders, in my own garden, I added two native vines--groundnut and Virgin's Bower (Clematis virginiana)--that have some wonderful qualities but turn out to be aggressive underground spreaders under sunny conditions. Autumn clematis--a nonnative very similar to Virgin's Bower--also can be super aggressive underground. And then there are the perennial sunflowers, and many kinds of mint. Native or not, they too establish large sprawling underground root systems that send up lots of new shoots the next year in places you really don't want them. 

A satisfying garden, just like a satisfying habitat, is a conversation among many species of plants. I like to think of myself as a moderator, and though I have a general vision for how the "discussion" will go, I don't have the time or inclination to exert strict control. When one species of plant takes over, the feeling is much like someone who takes over a conversation. There's a narcissistic quality to an aggressive plant, a Me, Me, Me indifference to what other species have to contribute. Dominance by one species has ecological impacts as well. Loss of plant diversity strips a habitat of the progression of blooms that might otherwise sustain pollinators through the summer and feed a diversity of herbivores. 

What to do about aggressive underground spreaders? One can play a war of attrition, in which the vigilant gardener deprives the underground root system of energy by pulling all shoots as soon as they emerge. Over time, the root system, needing to continually burn energy in order to survive, exhausts itself for lack of energy inputs from above. Since vigilance is hard to maintain, a more sure approach is to lay cardboard over the whole thing, cover the cardboard with mulch, and wait a year. 

Both of these approaches can help, but neither is very practical in most situations. For our own bodies, we sometimes need to take medicine to knock out a pathogen. The same holds true in a garden, where some careful spot-spraying with a systemic herbicide can kill the entrenched root systems of these underground insurgencies. Again, this is a minimalist, medicinal use of herbicide, not the chemical treadmill often aimed at asserting total control over nature.

The work involved in countering the aggressive spreaders makes the gardener really appreciate all the wildflowers that stay where you plant them. The aim is to get back to a garden where many kinds of plants coexist in relative harmony and balance. Catch the aggressive spreaders early, and gardening becomes much easier.

Looking Down On a Lawn

A lot of people, if they could see it, would look down on the nature of my backyard lawn. It at least meets one of the criteria of a lawn, in that it is regularly mowed. When looking down on a lawn, or "lawn", one might as well identify the plants growing there. Warning: The photographs you are about to see may appall those who take pride in a lawn's appearance and pedigree. There is True Green, and then there is the Green Truth, herein depicted in unflinching detail.

Broadleaf plantain (Plantago major),

 a mixture of white clover and violet (human grazers will find the violet leaves and flowers more tasty than turfgrass),

 wood sorrel (each leaflet is heart-shaped, while clover's are round). Wood sorrel has a taste made sour by oxalic acid, and is different from sorrel.

If mock strawberry, an inedible strawberry from India, is allowed to spread, it creates a kind of green pavement, growing low enough to survive beneath the mowing blades.

Three-seeded mercury, along the edges of the lawn.

Lest anyone think the lawn entirely devoid of grass, there are patches of Japanese stiltgrass, with its broad leaf blades--the same annual species that carpets woodlands--

and nimblewill, a blueish green, narrow-bladed grass.

The yellow-green blades that become prominent in lawns in late summer are nutsedge, another non-native.

Nutsedge is very easy to pull out, but if allowed to grow to maturity, it looks like this.

Another prosperous weed that has made surprising inroads into the lawn this year is heal-all, a prostrate plant in the mint family that likely originated in Europe (rudely left out of the photo shoot).

All of these excel at playing Lawnmower Limbo.

Princeton's Fuel Tank Raingarden Threatened By Lack of Early Intervention

A couple years ago, the town planted this raingarden next to the fuel tank on Witherspoon Street. They put in some pretty cultivars of showy native species like black-eyed susan, purple coneflower, and St. Johnswort, then mulched it all carefully. Everything looked under control, as gardens do when they are first planted.

Even this summer, with flowers blazing, it looks like a success. 

But I can see that the seeds of its ultimate demise have already sprouted. This botanical drama has played out many times before--raingardens that failed for lack of strategic intervention when aggressive weeds started to move in.

Most deadly is the mugwort that has become established and is quickly spreading. That one invasive species alone could obliterate the intended plants in a few years.

Nutsedge, too, spreads rapidly.

Along with foxtail grass, 

and barnyard grass, the nutsedge is obscuring a nice stand of soft rush the town planted two years ago. 

More easily dealt with are the ragweed--a native weed with allergenic green flowers--

a flamboyant patch of crabgrass, 

and what looks like a patch of black medic. The mulch laid down two years ago surely helped, but its capacity to stifle weed growth clearly didn't last.

And what's this vine, crawling out over the other plants? Ivyleaf morning glory is a new one for me. 

Back in late April, when this photo showed the mugwort looking tamable, pullable, sprayable, I alerted the town that early detection and rapid response is what's needed to keep the weeds from taking over. The response was that a public works crew weeds the garden once or twice per year. That's not how a raingarden works. I know from long experience. Catch the aggressive weeds early, and the raingarden will ultimately become very easy to maintain. 

Vikki Caines, a longtime member of the Recreation Department who recently retired, kept beautiful gardens growing in areas near the community pool. But that was a labor of love, done in her spare time. It's love, of a parental variety, that leads one to acquire plant knowledge in the first place, and then to grow a garden and anticipate its needs, and check for weeds, much more than once or twice per year. 

How can your typical institution--where staff lack plant knowledge, motivation, and the flexibility in routine needed to catch problems early--successfully tend to a botanically complex raingarden planting? For the past 30 years, I've watched as many native raingardens and meadows planted by towns or universities have incrementally failed for lack of early and ongoing intervention by a knowledgeable caretaker. Maintenance requires more knowledge than installation, because the caretaker must know not only the intended plants but also the many species of weeds that inevitably try to move in. Yet we see over and over that money is invested in design and installation, while maintenance is deprived of funding and respect. We have doctors and nurses to care for people, but precious few plant doctors to care for landscapes. 

A bit of good news: Last year, I wrote a google review of the Betsey Stockton Garden planted on top of the Princeton University's Firestone Library, pointing out that white clover and other weeds were invading the flower beds. Whether the review had an impact, I can't say, but the university is taking better care of the meadow planting this year.

Related Posts:

Princeton Finally Plants Its Fuel Tank Raingarden

Princeton's New Neuroscience Building Has Thoughtful Native Plantings

Followed two years later by:

Where Have All the Flowers Gone at the Neuroscience Building?

Weeding With Confidence--Part 1

To weed a garden requires knowing what to weed out. A weed is defined as "a plant out of place," which means that most any plant could be called a weed if it's not growing where you want it to.

In this garden, the preference is for plants that are native to the region, have some attractive attributes, don't grow into trees that will shade everything else, and don't spread aggressively by seed or rhizome.

So let's look at this photo of plants that popped up this spring. It's a mix of native and non-native species--Virginia creeper, willow herb, wood sorrel, nutsedge, violet, and one seedling of cutleaf coneflower. Since they're in the middle of a garden path, they all came out. Virginia creeper (five leaflets, lower lefthand corner) is a native vine that's fine for untended areas, but much too expansionist for a garden. Nutsedge (grassy looking leaves, light green) is a non-native sedge that pulls up easily but keeps popping up, requiring eternal vigilance. Wood sorrel (clover-like leaves) is a ubiquitous presence in gardens and greenhouses, with a little yellow flower and acid taste. Willow herb (narrow leaves in pairs) is a weedy native that sprouts abundantly from seed. It has a promising form but miniscule flowers. Violets are attractive and tasty, but not in a garden path.

Only one plant was worth potting up for later use--the cutleaf coneflower seedling, its two broad, oddly lobed leaves visible here in a blowup from the original photo. If given a good place to grow, it will become a tall, stately wildflower bedecked with bright yellow flowers. The seedheads in turn attract a second wave of yellow, in the form of goldfinches vying for a snack.

To Save a Raingarden, Know Your Weeds

This is one of several posts intended to show how a knowledge of weeds can boost one's confidence as a gardener. The more confident gardeners we have in Princeton and elsewhere, the more gardens are likely to survive. Photos of some common weeds are below, but first, some background.

A number of local, designed native plantings have been mowed down in the past year or two. Examples include plantings at Princeton University, Harrison Street Park, and Westminster Choir College. The latter is featured in this post.

As with recycling programs, that mundane-sounding activity called maintenance determines success or failure. Without skilled, attentive management, all those lovely designs are just whistling in the wind. Though design and installation get all the respect and publicity, maintenance requires far more skill, because the gardener needs to know not only the intended native plants but also the dozens of weeds that will inevitably show up. Furthermore, each species must be recognized in all its different life stages.

How shall we define a weed? Since the intention of this raingarden is a mix of function (filter runoff from the pavement, provide some habitat) and ornament, a weed here is defined as a plant that lacks ornamental qualities and/or proves too aggressive. Even an intended plant can later be considered a weed if it becomes too aggressive in a particular situation.

If one stays on top of things, these plantings are relatively easy to maintain. But allow aggressive weeds like mugwort, bindweed, Canada thistle, or crown vetch to get established, and the owner will sooner or later decide it's all too much trouble, and mow it all down. Lawn is the ultimate control of a seemingly unruly nature.

This is what happened at Westminster Choir College's raingardens. Walking our dog, Leo, I watched over several years as the weeds moved in, competing with the intended wildflowers and switchgrass. Last year, the amaranth grew 7 feet tall. That must have done it, because this year, everything was mowed to the ground.

I had offered my services before, but this year I reached out to the sustainability director at Rider University, of which Westminster is a part, and offered to weed the raingardens and gradually shift them back to natives if they would commit to not mowing. She agreed, and the mowing stopped. Essentially, I had just acquired a new pet, a hybrid between tame and wild, requiring considerable human intervention at first, but less as time goes on if the "parenting" is good.

The resulting growth would be a bit intimidating for anyone who doesn't know plants. There's a sea of crabgrass, nutsedge has an ominous foothold, the amaranth is again showing vertical ambitions, but amidst all this are some promising signs. Blue vervain is making a comeback, attracting skipper butterflies,

and a robust ironweed is poised to flower in its new freedom from the lawn mower.

Below are some of the weeds to be contended with. Different strategies are required, depending on the species. A few weeds, like pilewort, three seeded mercury, and horseweed, are native, but most are introduced.

Crabgrass! Note the horizontal growth form and the finger-like seedheads. No attempt to control it, given it's vast numbers. It's an annual, so will die this fall and hopefully be less of an issue next spring as the intended plants begin shading it out.

Green amaranth overgrowing a blue vervain (yet to flower). It helps to note the smooth margins of the amaranth's leaves, contrasting with the toothed leaves of the vervain underneath it on the right. Also, a different shade of green.

All the amaranth came out, because it would be unsightly if allowed to grow tall, and thereby give Westminster an excuse to begin mowing again.

Fortunately, it had rained a couple days prior, the soil was sufficiently soft, and their taproots yielded to a slow, firm tug. Since weeding is so much easier after a rain, a flexible maintenance schedule can greatly reduce the work needed.

Pull with your arm, not with your back.

Horseweed has had a great year in farm fields and empty lots, and is vying for space here. Pull before it can set seed.

Nutsedge spreads underground, invading lawns and flower beds. Pulls easily, but likely will pop up again, a bit weaker each time. It's a bamboo situation in miniature, requiring that one steadily deprive the roots of energy from those solar panels called leaves.

One of my favorite edibles, lambs quarters. Either pull or leave a few to munch on. Can get way too tall, though.

Barnyard grass is not particularly aggressive, but is best pulled.

A species of smartweed. These Polygonums tend to be problematic, and sometimes very aggressive. Likely to get pulled.

There are different kinds of thistles. This is not the dreaded Canada thistle that invades with its underground rhizomes, but will likely come out if I remember to bring gloves or a shovel.

Three seeded mercury is a native annual with a weedy look to it.

Surely a mint, with the characteristic square stem, probably catnip, with the tiny flowers of horseweed in the background. Only one in the whole raingarden.

The weeding session took less than an hour, given the raingarden's soft soil. Maintaining a raingarden is 90% knowledge and strategy, 10% work. Know your weeds and their potential for being problematic, time the weeding for when the ground is soft and before the weeds spread or set seed, and pretty soon the raingarden will be giving a lot more than it takes. These are the principals that have worked in the past, and are now being tested at Westminster.