Ecological gardening

 While snow blankets the garden, it’s all potential. Dreaming of spring, I’m enjoying reading about ecological gardening—what I’ve been calling sustainable gardening, but I like the new term better. As Kelly Norris writes in a recent article in Fine Gardening, ecological gardening means understanding plants as part of a community, not just building blocks for an aesthetic composition.

 

Native Joe Pye weed in an ecological garden

    Goals I currently aspire to achieve in my ecological garden include promoting and supporting biodiversity, helping to keep air and water clean, sequestering carbon, minimizing my garden’s carbon footprint, conserving water, and preventing stormwater runoff. Since these are inherent functions of natural systems, the good news is that gardening this way should be less work, not more.

 

Leaf mulch conserves soil moisture and provides shelter for native insects

 
    Native Plant Trust and the Woodwell Climate Research Center have been researching how these goals can be accomplished in suburban yards in their Yard Futures Project. They’ve chosen yards in six cities: Boston, Baltimore, Minneapolis-St. Paul, Phoenix, Los Angeles, and Miami. The lucky chosen ones get a visit from a team that’s prepared to observe and document what’s living on their property, from birds to insects to soil organisms. The goal of the research is to document the current state of backyards in a range of climate conditions and discover how suburban properties can best support a healthy environment.

    I wish my yard had been chosen! I’d love to know what experts could find there. In one visit, they could detect and document far more than I ever will. But I’m hopeful that my yard would show lots of biodiversity, because I’ve been trying to put out the welcome mat with native plants and gardening strategies that imitate natural processes.

 

Virginia bluebells

    To take it up a notch, I can start to think more about how plants weave together in natural settings. For example, when choosing a perennial, I pay attention to whether it’s a spreader. That might be a red flag for a traditional garden, but for creating a ground cover layer in a naturalistic ecological garden, it can be an asset. But I don’t usually ask whether a plant is tap-rooted or rhizomatous, grows singularly or in colonies, is short- or long-lived.

 
     In nature, plants fill every available space, above ground and below, gaining from each other’s contributions and maximizing diversity. Instead of fields of mulch punctuated with separated plants, ecological gardens are a mix of tall and short, broad and upright, early and late-developing plants, similar to what you’d see in a wild setting.

 

Plants knit together in an ecological garden

    This doesn’t have to look like a mess. By maintaining clear edges and growing large swathes of species that flourish in site conditions, ecological gardeners are creating gardens that are “legible”—appealing to viewers as designed spaces.

    So for this spring and summer, I’m thinking about how to fill up beds with more—more low spreaders, more early bloomers for the first pollinators of the year, more self-seeders. They should be native plants, but that’s not all. They should contribute actively to the plant community.

 

For the pollinators

 

 

 

Working together

Come visit my table at Celebrate Newton, a holiday craft fair, this Sunday December 2 from 10 to 4.

I realize that I’m prone to thinking of the plant world in terms of competition. I suppose this is an over-simplification of Darwinian thought: we picture the garden as a battle for resources where the fittest survive. Experience bears this out when we see aggressive plants-- nonnative invasives but also native plants and imports that happen to be in their best growing environment--crowding out plants that are less well-suited for a particular niche in time and space.

Sweet woodruff ruling the shade garden

    As I learn more about the science of soil and plant communities, though, I find that there’s a lot of cooperation in addition to the competition I tend to notice. The first hint came in junior high, when we were taught the concept of symbiosis through the example of lichens, which, we were told, are a cooperation between fungi and algae. As lichenologist Trevor Goward says, “Lichens are fungi that have discovered agriculture.” The algae provide the fungi with energy through their photosynthesis, and the fungi provide protective structure. It turns out there’s a third partner in this cooperative effort, recently discovered. It’s a kind of yeast.

Lichens are a cooperative effort-photo Alex Proimos

    But there’s more. In The Hidden Life of Trees, forester Peter Wohlleben describes trees as social beings that share nutrients and warn each other of impending danger through their roots. Teaming with Microbes, a fascinating and useful book by Jeff Lowenfels and Wayne Lewis, describes the soil food web, the network of soil organisms that work together to provide plants’ roots with needed nutrients. Each soil organism has something to gain in the complicated transactions going on in the top few inches of soil.

Soil microbes-photo courtesy of Pacific Northwest National Lab

    Fungi called mycorrhizae grow in symbiosis with roots, providing water and nutrients in exchange for carbohydrates made by leaves. Free-living fungi, bacteria, nematodes, protozoa, small insects, and earthworms all seek food for themselves and, as a byproduct of their labor, provide food for others in the network. Each organism has evolved to play its part. It’s interesting that evolution has favored cooperation in this system, not just competitive success.

Fungi play an important role in decomposition

    Above ground there are similar processes at work. When we plant perennials, we tend to think they need plenty of space so they won’t have to compete for water, sunshine, and nutrients as they get established. 

Perennials spaced out for traditional planting

A newer, more natural way of planting recommends closer spacing of different kinds of perennials to form plant communities.

    Some perennials grow upright and tall, others make wide rosettes of leaves or hug the ground and weave their stems between taller growers. Some have taproots that grow straight down, many others create a mat of slender root fibers. Some take off fast in newly open ground, others grow more slowly but persist longer. 

Perennials with different growth habits can grow close together

By working around each other in space and time, the plants get what they need and also help each other by providing shade, edging out intruders, and holding moisture in the soil. In community there is strength.

To cram or not to cram

My new perennial bed is approaching its first birthday, and I’m taking the opportunity to assess how it’s doing. Just about all of the plants made it through the winter, probably because the project was blessed with adequate rainfall in fall and spring and good snow cover during the winter. 

Bulking up for summer

I’d like to believe that letting a thick layer of whole leaves lie on the bed through the winter also helped the young plants.

    Now I’m seeing flowers on the new perennials and low shrubs. A yellow shrub rose (‘Kolorscape Yellow Fizz’) is blooming, 

and blue-eyed grass (Sisyrinchium angustifolium ‘Lucerne’)is covered with purple flowers.

Yarrow (Achillea ‘Coronation Gold’) is covered with buds that are about to open. One of the things I love about this new bed is its relatively sunny exposure. There are few spots in the yard that get as much sun as this area right off the back deck. I was able to choose species that need direct sun for at least part of the day, and they’re getting enough sun to flower generously.

    I tried to restrain myself from planting this new bed too densely. In the past, I’ve often crammed in so many plants that they suffered from lack of space. The more aggressive growers tended to take over, shading out the timid or out-competing them for root space and access to water. That’s one way I learned what will grow in my yard and what won’t. What’s here now is what survived.

    Over-crowding is hard to resist, because there are so many plants I’d like to grow and only limited space to put them in. This time, though, I tried to think about the mature size of the plants as I placed them in the bed. As a result, they’re currently surrounded by lots of open space. They should fill in by their third summer.

More mulch than foliage this May

    Thomas Rainer and Claudia West, on the cutting edge of landscape design, advocate a different approach to plant spacing in their book Planting in a Post-Wild World. They argue for cultivated landscapes that evoke archetypal natural plant communities, such as grasslands, shrublands and forests. Instead of making the soil and site hospitable to a list of favored plants, they match plants to existing site conditions.

    There are no open mulched areas between plants under their scheme, and there's no bare soil. Their herbaceous layer, which features perennials and grasses, is surrounded by low, spreading species that fill in all the gaps, both above ground and in the root zone. By allowing each type of plant its niche, they achieve a landscape as dense as a patch of weeds. Some plant uses every inch of soil.

All niches are filled as this lawn returns to nature

    As it happens, I did choose some low-growing native species for my bed: bearberry (Arctostaphylos uva-ursi), American cranberry (Vaccinium macrocarpon), and three-leaved stonecrop (Sedum ternatum ‘Larinem Park’).  

Who knew cranberry plants were so pretty?

I’m watching to see which will grow best. Perhaps they’ll weave themselves into the kind of tapestry Rainer and West describe.

Bearberry reaching out to surround taller perennials

 

Soil needs plants

As I become more aware of the “underground herd” of soil organisms, I’m changing my perspective on soil, looking at it as a living system that interacts with plant communities. Two recent paradigm-shifting books shed light on this approach. They are The Living Landscape, by Rick Darke and Doug Tallamy, and Planting in a Post-Wild World, by Thomas Rainer and Claudia West.

    To my surprise, I learned from Rainer and West, “When soil is exposed to sunlight, rain and extreme temperature changes, it is damaged,” and its stored carbon is oxidized and released as carbon dioxide. “The longer a soil is exposed, the harder it is to vegetate later.” 

    Like many suburbanites, I’ve had the fond belief that unplanted areas would be fine for indefinite periods if they’re covered with mulch. 

I thought mulch was enough to protect soil.

Apparently this is better than leaving soil bare to the elements, but it’s not the best approach. 

    It seems that roots and plants’ “underground storage organs” (more on this somewhat risqué phrase in a future post) are crucial for building functioning soil. The channels dug by roots open up space for air and water. When roots decompose in fall and winter, their organic material stays behind as humus, storing carbon and nutrients in the soil. That’s good for plants and good for the climate, too.

Dense groundcover is healthier for soil

    Both author duos describe natural landscapes in terms of plant layers. Among the broad landscape types, my yard is closest to a woodland edge. In this kind of landscape there’s a canopy layer formed by trees, a woody understory of lower trees and shrubs, and an herbaceous layer of perennials and grasses, ranging down to the lowest plants that cover the ground. 
  
    This week I moved some bearded iris that were blocking our view of the fish pond and replaced some tired moss phlox (Phlox subulata) with five pots of bearberry (Arctostaphylos uva-ursi). Their spot is one of the most visible in the yard, within clear view of the kitchen windows. 

The fish pond in August

The bearberry plants join the groundcover layer, and I hope they’ll stay low and neat-looking. I had pulled out some moss phlox a few weeks ago and left the soil bare before covering it with bark mulch last week.

Bearberry and bare soil. I hope it will fill in next spring.

    Both sets of authors emphasize the benefits of a rich and diverse groundcover layer for providing habitat for insects and other small organisms. Native bearberry should help in this regard. I’ve certainly got lots growing at ground level. Over the years I’ve planted something in just about every inch of garden soil. 

    When I squeezed in those little plants I couldn’t resist bringing home, of course, it was to help the environment. As one of this year’s presidential candidates would say, “Believe me!”  And I’m willing to do even more shopping for the sake of the earth.

Great oaks from little acorns

I just learned that one out of 10,000 acorns grows into a mature oak tree. That’s not great reproductive success. A mature oak, fifty years old or more, produces thousands of acorns every year, up to 10,000 in a boom or mast year, which occurs every three to five years in red oaks. One reason that few acorns grow into adult oaks is that so many become food for wildlife.

            An eastern red oak (Quercus rubra) happens to be one of the keystone trees in my yard, more than 100 years old and standing close to the house. I used to resent its shade. 

This red oak, our tallest tree, is older than the house.

Now I see it not just as an individual but as a whole community, including a housing project and grocery store (or maybe a community-supported agriculture cooperative) for wildlife I want to support.

            At this time of year, acorns are starting to ping off the metal roof of the garage, and the ground under the tree is littered with them, making for a lumpy surface underfoot. 

Red oak acorns

Red oak acorns take two growing seasons to mature, so the ones on the ground today sprouted two springs ago. White oak acorns (Quercus alba), the other type common in my area, develop in a year.

            At least ninety-six North American animals feed on oaks, eating acorns, twigs, buds or bark. White oak acorns are sweeter than those of red oaks, and they get gobbled up by squirrels and other creatures as they fall. Red oak acorns are bitter, because they contain more tannin. They retain their food value through the winter; animals can eat them in spring when all the tasty white oak acorns are gone.

            The oaks benefit from providing nuts that animals want to eat. Researchers observing jays found that each bird transported and cached around 110 acorns per day. The acorns the jays hid—they prefer to bury them in soft, moist soil—were more likely to germinate than acorns that fell under the tree. Squirrels dig holes in my garden to hide acorns, and some of them do sprout, although they’re far outnumbered by Norway maple seedlings.

Two white oak seedlings in a neighbor's juniper bed

            Besides feeding the birds and mammals that visit my yard and eat acorns—jays, crows, wild turkeys, squirrels, raccoons, chipmunks, rabbits and opossums—oaks are the best tree hosts for native insects I’d like to attract. Oaks support 534 butterfly and moth species, and there are 600 insect species that use oaks as their only host plants.

            As our red oak loses its lower limbs with age, its shade at garden level becomes more diffuse. In addition to all the ecological services it provides— improving air quality, modulating temperature, and sequestering carbon, to name a few--it’s now supporting a 30-foot climbing hydrangea (Hydrangea anomala subsp. petiolaris). I’ve learned to think of the giant oak as an essential part of my garden’s habitat.

The base of the red oak is hidden by the climbing hydrangea clinging to its bark.

It takes a plant community

Sometimes it feels like we’ll never get ahead of opportunistic nonnative plants. Especially with woody plants like Japanese knotweed (Fallopia japonica), it seems once they’re in your garden, you may never see the end of them. 

            In his book Gaia’s Garden, Toby Hemenway argues that opportunistic plants grow where we’ve given them an opening in disturbed ground and will naturally die off as stable plant communities take over (Hemenway prefers the term opportunistic to invasive, which he considers too emotionally loaded. I’m using his terminology). This is a nice idea, but considering how much Japanese knotweed I see in the course of a week’s driving, I wondered how likely Hemenway’s scenario was in my area.

This Japanese knotweed's underground rhizomes could be as much as 60 feet long. It propagates by seeds but is also capable of regenerating from root or stem fragments.

          
          This week I was pruning dead branches out of a dwarf mugo pine, (Pinus mugo 'Paul's Dwarf') planted eighteen years ago that is now partially shaded by a nearby magnolia. It occurred to me that this could be an example of Hemenway’s point. The branches that were in full shade were dead, with clinging brown needles, whereas the side of the little tree that was still in sun was looking good and producing green needles. I hadn’t shaded out this pine on purpose, I’d just failed to imagine how big the two trees were going to grow and planted them too close together.

Mugo pine reaching for sunlight outside the shade of a taller magnolia

            If the magnolia had cast its shade over an unwanted shrub like Japanese knotweed, I suppose it too would have dwindled. The problem, Hemenway points out, is that suburban landscapes, even our parks, offer so many sunny edges that favor fast-growing plants like the knotweed.

            Of course, shade isn’t the only condition that discourages opportunistic plants. The goal is to replace a plant that you don’t want with one, or ideally some, that you do. If you just remove the offender, you leave open soil for opportunists to take over again. Growing together, a group of native plants that have evolved to cooperate can succeed in grabbing the resources an opportunist needs to survive, not just sunlight but also water, soil nutrients, and room to grow.

            While I wait for my growing collection of native plants to knit themselves into anti-opportunist communities, I’m still cutting a couple of knotweeds at the fence line to the ground every couple of weeks, hoping they’ll eventually run out of stored energy and give up.

I cut it down, but this deceptively frail-looking Japanese knotweed, center, keeps coming back up. Will encroaching smooth Solomon's seal help to curb its growth?