Policing or editing?

Where should weeding stop? I confess I have trouble stopping myself from pulling out certain weeds, even when they’re not on my property.

One I missed this spring

            My number one target is Norway maple (Acer platanoides). Starting in April thousands of its offspring peek through the groundcover in front of the house, sprout in the compost pile, and even poke up in compacted areas of the lawn. As I move around the garden in spring, I clutch an expanding bouquet of the little seedlings. If I miss them their first year, they’ll be back the next spring woodier and harder to pull out.

            Cities chose Norway maples as street trees because they can tolerate urban conditions. Can they ever! Fence lines and hedges around the neighborhood bear witness to what happens if you ignore their seedlings for a few years—they soon grow tall and out-compete everything below, blocking the sun, hogging the water, and spreading their phytotoxins, chemicals they exude that prevent other plants from growing. 

            I find it hard to keep my hands off the multitudes of Norway maple seedlings I pass in other people’s front yards as I walk my dog. Ailanthus altissima 
(tree of heaven, the tree that grew in Brooklyn), another rapacious grower, also makes me want to yank it out. 

            But how would I feel if someone else weeded my garden without my permission? Outraged and insulted. So I try to hold back. I don’t always succeed.

            All this weeding makes me ask whether I’m trying to police the world. Gardeners reserve the prerogative to decide what grows in their gardens. Outside the garden gates, though, should we stay out of it and let the strong survive? 
            Roger Swain, whom you may remember as the host of the PBS show The Victory Garden, wrote about “editing” a patch of woods on his New Hampshire farm. He subtracted trees and shrubs in March to incline the population toward the native plants he wanted to foster. This seems like a sane approach to the plant world. But when he was in Lexington to film the TV show, I wonder if he found himself twitching out Norway maple seedlings.

           

           

    

          

           

           

    

Learning to love shade

When I moved into a new house in 1985 and started my garden, I was disappointed to find that my fifth of an acre lot was mostly shady. The Norway maples in the curb strip effectively shaded our small front yard. In back, we had mature trees to the west, north and south, leaving a patch of lawn between the back fence and the house that got sun in the middle of the day. My first attempt to grow flowers was in that patch of sunnier ground. 

I wanted to grow roses and sun perennials. It took a long time to recognize that I was gardening in shade, whether I liked it or not.

            Some of the trees around the yard were on our property, so we could have cut them down. For each, there was a reason why we chose not to. A line of droopy Norway spruces blocked our southern exposure, but they also created a privacy barrier between our yard and our neighbor’s house. Next to the garage stood a red oak that an arborist guessed was at least 100 years old. Was I really going to evict every creature that depended on that venerable tree? Behind the fence to our west was a thicket of Norway maples rapidly growing from seed on our neighbor’s land.

            So shade gardening was my fate. I learned to love a lot of woodland plants and to seek out attractive leaf forms, textures and variegations. 

 Then we got a surprising opportunity to expand our lot to a third of an acre by buying some land from the neighbors behind us. After we cut down the Norway maples around the perimeter of our new land, I had something I’d never expected—a place to garden in almost full sun.

            But instead of putting in those English-style deep perennial borders full of sun-lovers, I went out and planted a lot more trees. We wanted a visual barrier along the back of the new lot, so we built a berm and planted evergreens including white pines, a balsam fir, and a blue spruce. I really wanted a gingko and a dawn redwood. For understory trees I had to have a stewartia, magnolias, redbuds, shadbushes, and witch hazels. By the time all that planting was done and the trees put on some height, my sunny garden area was mostly gone.

            I enjoy the variety of foliage that my shady garden offers. Later I learned about some other advantages of shade. Those Norway spruces along the south side of the yard shade our house in summer, decreasing our air conditioning bill. The berm to our west planted with now-tall evergreens shelters us from winter winds. A lot of New England’s worst invasive plants don’t prefer shade, so I have less of a battle keeping them at bay. The plants I grow in shade need less maintenance than sun-lovers would. And I’m certainly providing lots of shelter for animals, from insects on up to mammals. 

Kicking the peat habit

Mom, apple pie and peat moss? If you thought, as I used to, that peat moss is a renewable natural product, I’ve got some bad news for you. It’s time to break with peat-based potting soil.

            Peat moss was part of my gardening life from early on. It was the main ingredient of every growing medium I bought. But it turns out that we’re using it up, and contributing to climate change in the process. It wasn’t until I read Sarah Reichard’s book The Conscientious Gardener that I learned the sad truth.

            The problem with harvesting peat is that it's created so slowly. Peat comes from wetland plants—sphagnum moss but also sedges, grasses and reeds-- decomposing very slowly in oxygen-poor water. In peat bogs, peat forms at less than a millimeter per year; the peat we garden with took thousands of years to form. It’s hard to imagine sustainable harvesting given that rate of growth. 

Sphagnum moss growing at Eagle Hill Bog, Campobello Island, New Brunswick

Peat sequesters one third of the world’s soil carbon, more than all the trees in the world. When the peat is harvested, the carbon is released and the carbon sink it provides is eliminated.

            Swarthmore College, whose campus includes Scott Arboretum, has stopped using peat-based potting soil and switched to a mix of coir, or coconut fibers, worm castings, mushroom compost, and rice hulls. Eventually peat-free potting soil will be widely available in the US. In Britain it's already mainstream.  
            Until we catch up, I decided to make my own peat-free mix, using a basic combination of one part coir to one part screened compost from my own yard. A local hydroponic gardening shop provided bagged coir. A by-product of coconut husk processing, coir is the pith left over after separating out longer fibers for use as bristles, filaments, mats, padding, and biodegradable textiles.

            Right away I could see why this material would make a plausible substitute for peat. It’s almost the same color and consistency, a little redder and coarser. Combining coir and compost yielded a handsome, fluffy rich brown mix that already looked absorbent. I used it to pot up annuals, cannas, and elephant ears. One thing was immediately evident: my potting mix was not sterile or weed-free. My compost hadn’t heated up enough to kill weed seeds. In every pot, sprouts began to surface, but the weeds were easy to pull out.   

            By the end of the growing season, I was convinced that my containers had done just as well using the coir and compost mix as they had in previous years with commercial potting soils. I don’t miss peat, because the new mix seems to work fine.  

Be careful what you wish for

          One gardener’s ideal plant is another gardener’s nightmare. 

          More times than I’d like to admit, I’ve planted what I thought would be a useful groundcover and found it taking over. Two examples are sweet woodruff, Galium odoratum, and smooth Solomon’s seal, Polygonatum biflorum. I planted them because my yard is shady, and they promised to thrive in shade.  Thrive they did.  Smooth Solomon’s seal is native to the eastern US. I found it quite pretty, with its arching stems and modest white flowers hanging below shiny leaves.  

Smooth Solomon's seal

 Perhaps its description as “rhizomatous” should have warned me. Actually I didn’t do any research, just scooped it up from the shade plant section at a local garden center. At first its spreading pleased me, and I gave away divisions to neighbors. Pretty soon I realized it was popping up all over the garden. 

            Sweet woodruff, a European import, took longer to start to move. The little plants looked so delicate when I bought them from a mail order nursery that I wondered if they’d survive. The whorls of little pale green leaves were adorable, and that May I was delighted with the starry white flowers held above the foliage. 

Sweet woodruff

 Later I found a warning that sweet woodruff could be aggressive in the right growing environment. For years it spread gradually, until suddenly I looked up and realized it had taken off in all directions. 

          That’s the catch.  Something about my yard in particular makes an ideal home for smooth Solomon’s seal and sweet woodruff, but a few houses down, they might be well-behaved, useful groundcovers for shade. You can’t always know from other people’s experience, and it can take years before a seemingly innocent little thing shows its colors. Conservation biology confirms this phenomenon: a species has to build a colony of significant size before its population suddenly surges. It’s one reason we get suckered by exciting new imports.

          But let’s face it, the whole groundcover idea involves playing with fire. We’re looking for a plant that spreads willingly, but we also think it should stop when we want it to. Vigor is good, until it shades over into aggression. Invasiveness is really a spectrum, not a bright line.

        If I’m lucky, I’ll end up with a varied tapestry of groundcovers with different leaf forms, colors and textures. If I’m unlucky or inattentive, I’m likely to cover my whole garden with one of the strongest growers, which will look boring and be very frustrating to try to change. I tend to feel superior when I walk by neighboring front yards where shrubs are surrounded by oceans of mulch where nothing grows. What a wasted opportunity! And to me, it’s a sad look. But the joke could be on me—in twenty years, their shrubs may have widened enough to touch shoulders, while I’ll be trying to dig ever-so-native smooth Solomon’s seal out of my beds.