News from the preserves, parks and backyards of Princeton, NJ. The website aims to acquaint Princetonians with our shared natural heritage and the benefits of restoring native diversity and beauty to the many preserved lands in and around Princeton.
Each spring in Herrontown Woods, from April through May, we take part in the Great Garlic Mustard Pull. That's the effort, replicated in yards and nature preserves throughout the eastern U.S., to pull garlic mustard (Alliaria petiolata) out of the ground before it goes to seed. This post explores the logic, toils and unexpected pleasures, as well as the strategies that can make this annual gardening task easier each year.
We pull this nonnative invasive plant, with its aroma of garlic and mustard, because the alternative is too much to bear. Left unchecked, garlic mustard can take over a woodland or garden, altering soil chemistry and smothering native species.
People pulling the flower stems are surprised to learn that other, lower-growing plants coating the ground are also garlic mustard. Two very different forms of the plant are present at the same time. Unlike most herbaceous plants that are either annuals or perennials, garlic mustard is a biennial. That means it grows a rosette the first year, storing energy in its roots--energy that will be used the second year to send up seed-bearing stalks. After the stalk blooms and the blooms turn to seed, the plant dies, leaving copious seed for future generations.
Gardeners are often fooled at first into leaving garlic mustard be. The flowers are modestly attractive, and as they fade and turn into siliques packed with seeds, the plant too fades politely into the background. But wait a month or two, and the flowering stems turn into brown, skeletal remains that haunt the summer garden. By the time the gardener notices this blight, the seeds have already dispersed.
Much is made of the plant being edible. Young leaves can be used to make pesto and other dishes. Our friend Kirsten used it to make delicious deviled eggs. But in most situations, the plant's powers of proliferation quickly overwhelm people's appetites.
And so we pull, and pull. That's Herrontown neighbor Philip Smit in the photo. The aim is to get every last one, to ultimately exhaust the soil's supply of seed. Only with zero tolerance will the task get easier year to year. Here is where technique and timing come into play. If you pull hastily, or when the soil is dry, you may get the stem but not the root. This is an incomplete victory. That root will sprout new seedstalks that then too must be pulled. So we "grab low and pull slow", ideally pulling after rain has softened the soil, and hope to get at least most of the roots. Either way, it's important to return a week or two later to check for any resprouts.
And what to do with the pulled stems, whose seeds could still potentially mature? Bagging them is a lot of work and wastes energy to have them hauled away. This year, we've been putting them in trash bins, then rolling them to a pile. In case any of the seeds mature, the pile is located where the seeds won't wash down the hill, so any seedlings will all be in one spot.
I've heard stories of gardeners who pulled year after year, and yet the garlic mustard continued to sprout anew. Where would the seed come from? We speculated that erosion from heavy rains, or the diggings of squirrels, could expose long buried seed.
But another cause could be these miniature plants I've been finding. We pull the bigger plants and think our work done, but no. A second and even a third pass is needed over the course of weeks, with an eye out for these tiny plants.
There can be pleasure in the task. These two visitors to the preserve joined in one day. Kids, too, take to the pulling, seeking out the white blooms as if it were an Easter egg hunt.
We're grateful that some students from Princeton University's Outdoor Action--Will Aepli, Quest Starkey, and Zach Duscorsky--worked with FOHW board member Ben Schaffer and me to clear garlic mustard from the Veblen House grounds and the Barden. Inge Regan, Moss Gordon, Ninfa and Andrew have helped with a larger patch in another woodland we're restoring, behind Windy Top.
Invasive species can seem an impossible challenge, but if the invasion is caught early, and the garlic mustard is completely removed year after year, the work we do to protect 230 acres of public open space at Herrontown Woods and Autumn Hill Reservation becomes a little easier, with some satisfaction and even pleasure in the task.
This year, we're getting more organized about planting and growing sunchokes. They are also called Jerusalem artichokes, which is a persistent name despite their not being artichokes and not being from Jerusalem. Instead, they are a native sunflower species, Helianthus tuberosus. As the latin name implies, they combine the height and glorious blooms of a sunflower with edible tubers that have a nutty flavor.
Sunchokes are super productive, but also spread aggressively underground, which means that they could easily take over your garden if not constrained. Thus the idea of planting them in big plant pots, and setting them on cardboard as further assurance that the roots won't sneak out the bottom of the pots and start spreading into the garden.
With good soil, sun, and water, you may end up in late fall with a tub packed with sunchoke tubers. Then the question is how to get them out of the heavy tub, a few at a time. The clever but untested answer I came up with years ago is to cut the dead stems in late fall, turn the tub over, then leave it upside down through the winter. Upside down, the tub becomes a cover that can be lifted whenever you want an artichoke to eat raw or cook. This year, it looks like we might get organized enough to see if this approach works.
Here's a plant pot filled with the harvest this spring from last year's big black tub. I expect that more attention and prep will, as in past years, yield far more.
My source for tubers has been the produce section of the Whole Earth Center in Princeton. There's another variety, with reddish, more linear tubers, that I also have. Both taste good.
The journey of this blogpost began with a curious lone tree found standing along Nassau Street in late winter. I had passed by this spot many times, oblivious to what has long been there, tucked away in a courtyard.
Perhaps 20 feet tall and all knobby at the ends, the tree's silhouette looks more like something you'd see in Joshua Tree National Park than downtown Princeton, New Jersey. And those stubs of branches sticking out look more like a way to keep pigeons away than launchpads for new growth.
Though I have yet to inquire, it looks like someone cuts this tree each year at the same spot, so that it will stay the same size and not outgrow its confined space in the courtyard. Anyone who has traveled to Europe has likely seen this radical pruning of trees. Is this a form of torture or a clever and sustainable means of manipulating growth?
Meanwhile, in my front yard, there's a native shrub called a buttonbush that began to outgrow the spot where I planted it. Fortunately, buttonbush flowers on new growth, so you can cut it down as far as you want each winter and still get abundant flowers for pollinators in the summer.
Here's what it looked like before I cut all those long stems off to get it back to a manageable size next to the sidewalk.
I pruned another one in the backyard even more radically--almost down to a stump. And those long shoots I cut off, gathered on the right side of the photo? Those I use as "live stakes" to create new shrubs in the nature preserve we take care of, Herrontown Woods. Buttonbush, like the native silky dogwood and elderberry, has the wonderful quality of sprouting roots when pushed down into moist ground in late winter. Clip the above ground portion down to a couple nodes, where leaves will sprout. Easiest and cheapest new shrub ever, as long as you water it during droughts and protect it from the deer.
My radical pruning, then, serves two purposes. It keeps the shrub small, and produces a crop of highly useful live stakes for propagation.
By harvesting these live stakes, I was practicing a form of radical, recurrent pruning that dates back thousands of years, was once common worldwide, and has a name: pollarding. I've written about it before (see links below), but decided to cruise the internet in search of more info.
What I found were some delightful short videos produced in Norway that tell the story of pollarding and a related practice, coppicing, in a way that changed my view of Europe's relationship to nature. You see, I have long thought of Native Americans as being the ones who managed the land in a way that promoted biodiversity. Lacking saws and sharp axes, they primarily used fire--the low-level variety that I like to call mildfire--to open up canopies and promote lush growth of useful plants in the understory. Mildfires promoted the growth of fire-resistant, food-producing trees like chestnut and oak, while opening the canopy enough to allow sunlight to drive production of edible herbaceous plants and berry-producing shrubs like blueberries. These managed forests were likely far more productive and diverse than our dense "untouched" forests that may work for some species, but whose deep shade limits what can grow in the understory.
What I didn't realize, in this elevation of Native Americans as ecologically minded land managers, was that Europeans also had ancient ways of managing land that promoted biodiversity. Watch these animated 4-minute videos and you'll learn that the farmers' practices of radical pruning known as pollarding and coppicing allowed trees to live long and productive lives while also allowing sunlight to reach more diminutive but equally important plants. Coppicing and pollarding even proved beneficial for insects and birds.
The videos evoke a time when culture was married to local nature. There was an enduring relationship, a give and take. Year after year, for decades growing into centuries, farmers would tend to the trees. Unlike a typical forest today, in which most of the sunlight feeds growth far beyond reach, pollarding kept the trees' productive canopies closer to the ground, kept the branches smaller and easily cut so that the leaves could be fed to animals and the branches used for tools, poles, and firewood. To work, pollarding depends on consistent tending--a hardwired connection between people and nature.
Though I still encounter that hardwired connection in some people, more common is a relationship to nature that is distant, fleeting, and abstract--more aspirational than actual. Organized gatherings to plant a tree or a raingarden tend to be like one night stands, with little or no followup to insure that whatever was planted actually survives. While we import sustenance and lumber from distant lands, the local trees are called upon to provide services that are more sensory and psychological: to cool our air, heal our souls, and somehow miraculously compensate for our relentless injections of additional carbon dioxide into the atmosphere through tailpipes and chimneys. So disconnected is the economy from local trees that, when they are cut down, trees are immediately ground into woodchips, ironically expediting the return of their sequestered carbon to the atmosphere.
As the videos show, pollarding in past centuries not only made tree canopies accessible and useful. Harvesting branches in a grove of pollarded trees every 10-15 years allowed sunlight to reach the ground and power the growth of diverse understory species. Though we allow trees to grow naturally in local woodlands, we have limited our open space to only two options: the land is either a forest or a field, no inbetween. The inbetween is what would have been more common historically, when fire was allowed to play its ecological role in creating a mosaic of old-growth and younger landscapes. Pollarding appears to have been a way to replicate a more natural, ecologically diverse mosaic while directly sustaining a human community.
Now, if you check in with an American arborist about pollarding, you'll likely get a negative spin. Here's an informative example from Oregon of an American approach to tree care that promotes useful interventions like weight reduction, crown thinning, crown raising, and crown reduction. These methods of pruning preserve a tree's naturalistic growth patterns and shape. The practice of pollarding is also mentioned, but is placed at the bottom, and criticized as stressful for the tree, unnatural, unsustainable, unappealing, and leading to weak branch structure, instability and shorter lifespan.
This negative take on pollarding in the U.S. conflicts with the descriptions in the videos, which tell of coppiced or pollarded trees living for many hundreds of years and proving more resilient in storms. It also conflicts with my experience in North Carolina. When a hurricane swept through it was the pollarded willow oak that proved most resilient. Its many thin flexible branches swayed in the intense winds, while more naturally growing willow oaks with their bulky frames and massive canopies proved vulnerable. The trauma inflicted by that storm caused me to view natural-growing trees in our neighborhood differently--still as generous beauties but also as wild, untamed beasts we allow to grow amongst our houses.
As described in the videos, success in pollarding and coppicing depends not only on consistent care but also on the kind of tree. For coppicing, the video mentions European hornbeam, linden, chestnut, and hazel (Carpinus betulus, Tilia sp., Castanea sativa, Corylus avellana). There are American parallels to these: ironwood, basswood, chestnut (at least in the past), and hazelnut. For pollarding, another source suggests willows, London plane tree (related to our sycamore), American basswood, elms, and mulberries.
A culture such as ours, distracted and disconnected from nature, is not likely to foster healthy pollarded groves of trees like the farmers on the hillsides of Norway. But in a town where the open space movement was founded by a man whose last name comes from a farm in Norway, Oswald Veblen, it's worth demonstrating these forgotten methods of collaborating with nature. The sprout-happy buttonbush and a lonely tree on Nassau St are a good start.
