The Thinking (and Action) Behind a Successful Raingarden

In this post, we explore the thinking behind a successful raingarden. Thought has power, in that it sometimes turns into action, and so we will explore the thought behind the action that has made this large native planting thus far succeed.

In this case, it is a detention basin in Smoyer Park that was converted from turf grass into a wet meadow dominated by native prairie grasses with some wildflowers mixed in. Planted by Partners for Fish and Wildlife, this large-scale raingarden appeared sparse its first couple years, but has now grown thick and subtly colorful with time and attention.

Thick, that is, with intended plants, which is not a given when a raingarden is planted. How many gardens of all sorts, no matter how lovely the vision that brought them into being, have been taken over by mugwort, Canada thistle, and other invasive weeds? Having been this raingarden's volunteer caretaker for its first three seasons, as part of my work for Friends of Herrontown Woods, I visited it recently to see what needed to be weeded, and found nearly nothing requiring my attention. For a gardener, this state of affairs is almost unimaginable.

How could this be? Well, it helps to have planted a strong backbone of tall native grasses:

Indian grass

and big bluestem, to claim the space.

The caretaker's job then becomes a matter of influencing what other species come up in the spaces unclaimed by the grasses. Given limited time, a caretaker must learn to recognize each species and know from experience what to weed out and what to leave. Balance, beauty, and diversity are the goals. Some weeds like mugwort, Canada thistle, and crown vetch are notorious for taking over, and so were weeded out early in the game, before they could become too numerous and ruin any chance for diversity and beauty.

Others, like this fluffy-seeded, native but weedy pilewort that is growing lustily around the edge of the meadow, are judgement calls. I left it in, hoping it will behave like lambsquarters--another annual that makes a powerful showing one year but largely disappears the next.

(An example in this raingarden of a species that was numerous one year, gone the next, is black-eyed susan, which was in the original seed mix and generated lots of color before disappearing this year.)

There are a few native perennial wildflowers that have moved in on their own. At this stage, they are relatively few, and add spots of color and late-season nectar. But I don't entirely trust that they will continue to "play well with others." These include late-flowering thoroughwort,

a goldenrod species with narrow leaves,

and frost aster.

Providing bright color earlier in the season was one large specimen of false sunflower (Helianthus helianthoides)--commonly found in seed mixes for wet meadows. In another raingarden some years back I found it to be overly aggressive, but how it will behave here is yet to be seen.

A native annual I wish would spread around more is jewelweed, whose tubular orange flowers serve hummingbirds all summer long, and whose explosive seedpods delight anyone who takes one in their palm and touches it. Usually, the plant is rambunctious enough to survive the insistent browsing of deer, but for now it's huddling against the concrete outlet, chewed down before it can flower.

A "seed bombing" conducted by a girl scout troop in late spring may have been the origin of these young rose-mallow hibiscus (Hibiscus moscheutos),

and some ironweeds. These are local wildflowers we added to get more color and cater to the pollinators. Both of these can get tall, but may end up being kept low by deer browsing.

One of the pleasures in this wet meadow thus far, surely unnoticed by passersby and hard to photograph, is the clarity, by which I mean one can see inbetween plants all the way to the ground. Low-growing weeds like stiltgrass, carpgrass, ground ivy, and many others tend to muddle the planting, obscuring the ground. This clogged condition, the visual equivalent of listening to a scratchy record, has ecological as well as visual impacts. If the spaces between the bunch grasses are clogged with weeds, ground feeding birds have a harder time navigating, and can become more susceptible to disease from rubbing up against wet foliage.

An encounter with a garden that needs no weeding brings, for an experienced gardener, a mixture of feelings. There's surprise, some quiet pride and elation (that past interventions could have had such a positive effect), and a sense of foreboding. Surely I was missing something.

As it turned out, there was good reason for the foreboding. Getting ready to leave, I spotted a small patch of stiltgrass invading along one edge. Unlike lambsquarters or blackeyed susan, which can be prominent one year, gone the next, stiltgrass is one of the uber-invasives, an annual that grows ever more numerous with time, producing billions of seeds each year. Inedible to wildlife, it creates a stifling appearance, making a planting or whole woodland appear to be blanketed with green cobwebs.

Since its seeds were not yet ripe, I pulled as much as I could find out of the ground, then collected them all and threw them in a nearby woods where stiltgrass had already invaded. The source of the stiltgrass was actually the mowed lawn that surrounds our wet meadow. Given that stiltgrass can grow and seed even though only a few inches tall, the lawn is likely to remain a source of invasion for the foreseeable future. Since the weed prefers moist conditions, the more frequent and heavier rains we are experiencing due to global warming will only make it more aggressive. There continues to be hope that something--a fungus, an insect--will figure out how to consume it and thereby begin to bring stiltgrass into ecological balance, but that wait could be long.

These, then, are the thoughts that fill a wild gardener's mind when visiting a raingarden. Because the aggressive weeds were caught early--nipped in the bud, so to speak--the visits need only come once or twice a month for an hour, even for a wet meadow nearly an acre in size. Knowledge and experience make for strategic, efficient interventions. There's time left over to appreciate the bright flowers of partridge pea and the growing diversity. And it's satisfying to know that in a landscape dedicated to ballfields, a lowly bumblebee or the occasional monarch butterfly will still find some sustaining habitat when visiting Smoyer Park.

Spring Cleaning in the Raingarden

 One of the easiest and most rewarding spring tasks is preparing a raingarden for a new season of growth. This raingarden was installed by Curtis Helm and me at Princeton borough's Senior Resource Center on Harrison Street. Water from the roofs is channeled into the garden, where it accumulates to several inches in the hollowed out area and then slowly seeps into the ground. Mosquitoes are not an issue because the water does not stand long enough for them to breed. A list of the plants, all adapted to wet soils, can be found in another post.

All that was needed was a pair of pruning shears, gloves, and a plastic grocery bag that was conveniently found amongst all the paper and plastic trash caught by the raingarden over the winter.  

 Though the spring cleaning of a raingarden is easy and rewarding, I nonetheless postponed it until the last minute. One more week and the new growth would have become tangled in last year's dead stalks.

First step was to cut the brown stems of joepyeweed, green bulrush and other native perennials.

 It's important to check the downspouts that conduct water to the garden,

one of which had lost its underlying stones and needed a little tightening of the joints.

Pulling the occasional weed like false strawberry (Duchesnia indica, also called Indian strawberry, because it is native to India),

and gill-over-the-ground ( Glechoma hederacea, also called creeping charlie, or ground ivy) is a piece of cake if the soil is still soft after recent rains. 

Garlic mustard is a common weed that will spread by seed if not pulled out before it flowers. I've heard it makes good pesto, but have never tried it out.

 All that was left was to pick up the trash and toss the stalks back in the woods. No need to burden the borough crews with yardwaste that can easily decompose unnoticed back near a fenceline.

Less than an hour and it was done. Now to figure out how to make a raingarden grow cake.

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?

Harrison Street Raingarden in July

Another sight to be seen from Hamilton Avenue is the raingarden at Spruce Circle, just up from the intersection of Hamilton and Harrison Street. Type "raingarden" into the search box at the upper left of this blog and you'll find posts showing the raingarden in various seasons.

In July, the switchgrass (foreground) is fully grown, and the JoePyeWeed is in full flower (tall and purple).

A view uphill from the raingarden shows the long roof that feeds the garden during rains.

Here's a view from uphill looking down. Rain flows through the downspouts and out onto the grass, then down to the raingarden, where it collects and infiltrates into the ground over the next 24 hours or so, creating a nice underground reservoir of moisture to feed the roots of the wildflowers through droughts. Only in the most extreme droughts, such as the two-month long drought last year, does watering prove necessary.

Scattered through town, taking advantage of wet, sunny spots, raingardens like this one serve as lifelines for pollinators otherwise starved by the trees n' turf landscaping dictated by convention.

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.