A fair trade

Last weekend I attended a plant swap at New England Wild Flower Society. The society invited members to dig up some plants we could spare and bring them to trade with fellow gardeners. This turned out to be a lot of fun.

NEWFS's Garden in the Woods is a fabulous resource in Framingham, MA

    Each participant brought at least one plant, natives preferred but not required. We were each assigned a group number, 1 through 4. The offerings were varied, from garden favorites quite familiar to me to native plants for special locations such as swampy areas. When everyone had arrived and our group number was called, we dashed to the plant tables and each chose one plant. We took turns choosing until the plants were gone.

    I’d brought two wild gingers (Asarum canadense), two white-flowering phlox (Phlox maculatum ‘David’), a white bleeding heart (Lamprocapnos spectabilis ‘Alba’), and a goldenrod (genus Solidago) whose forebears I grew from seed years ago. 

Phlox 'David" blooms in mid- to late summer

     As I placed my offerings on the tables, I realized I’d be embarrassed if nobody chose them—like not being picked at a dance. I was relieved that they all found homes by the last round. Next year I’ll pot some plants in spring so they’ll look more appealing for the swap at the end of the summer.

    I came home with eight plants: a beautiful purple heuchera, a switchgrass (Panicum virgatum), a foxglove, a blue false indigo (Baptisia australis), two blazing stars (Liatris ligulistylis), a showy goldenrod (Solidago speciosa) and an Allegheny monkey flower (Mimulus ringens).

This well-grown heuchera was a prize

Besides a fun “shopping” experience and a chance to meet like-minded gardeners, the swap met two sustainability goals for me. First, I could be sure that none of my fellow NEWFS members had been spraying their plants with neonicotinoid insecticides before bringing them to the exchange. Neonics persist for a long time, but my hope was that these plants were either seedlings from the gardeners’ original plants, or they’d been around long enough to have outlived any pesticides they might have encountered at a nursery when they were young.

Native plant enthusiasts know not to poison pollinators with neonics

    Second, a swap like this gets around the carbon cost of garden center plants. Annuals and perennials we buy locally zip around the globe before they end up in our shopping carts. Growers may buy seeds from importers who source seed all over the world. They use tissue culture products imported from South Africa, Holland, Turkey, and Poland (tissue culture converts tiny pieces of plant tissue into large numbers of genetically identical plantlets). Large plantations in Costa Rica and Ecuador with space to maintain supplies of stock plants send unrooted cuttings for regional growers in the US to root and grow to saleable size.

Plants growing from tissue cultures-photo Daderot

    To produce high-volume annuals like petunias, breeders send cuttings to specialists at a rooting station, for mass production. A broker shopping on behalf of wholesalers or garden centers fills orders with rooted cuttings from multiple rooting stations.

    Unlike these international travelers, perennials from the plant swap really do come from the local area. And they’re free! A good deal all around.

This goldenrod grew up in my yard

Hell and high water

Photos of Houston afflicted by Hurricane Harvey reminded us of the worst that stormwater can do. It’s been pointed out that Houston’s unrestrained development created a set-up for flooding.

Flooding in Houston

Developers have been building in flood plains and paving over wetlands and prairies, reducing the chance for rain to soak into the ground. Smarter urban planning could have lessened the catastrophic effects of the hurricane.

Wetlands around Houston used to absorb stormwater--photo by Daniel Ray

    Did you know that China is a leader in this environmental area? They’re developing “sponge cities,” engineering ways to keep rainwater for use by water-poor cities, rather than letting it run off.  Besides cutting down on impermeable paved surfaces, they’re collecting rainwater in ponds and tanks and circulating it into the cities’ water supplies, either for non-potable uses or purified as drinking water.

    I hope it never happens, but if we got 50 inches of rain (a year’s worth) in a few days, the amount that fell on Houston, we’d want to let it soak through every possible surface.

Our deck and stone path, wet but permeable

Even without a huge hurricane, it’s better to keep rainwater on your property, because if it rushes down the street, it carries pollutants with it into nearby waterways. Here are some ways we gardeners can make our yards more sponge-like.

•    Make hard surfaces permeable. This is probably the most important change you can make. For us, the driveway is the main impermeable surface. By replacing a section of our asphalt driveway with porous paving material, we’ve enabled water to soak into the ground. 

Water sinks into the darker porous paving

A nice-looking alternative is to make a driveway out of stones with spaces between them where water can soak in. 

Paving stones let water soak through

Spaces between the stones of our new walkway similarly allow water to reach the soil below.

•    Direct water where you want it to go. If you’re an enterprising digger, you can create swales—basically trenches--to send water to your garden beds or to low-lying areas, where it will gradually percolate into the soil. 

Bioretention swale in Seattle during a 100-year storm

David Del Porto, an environmental visionary who designed an eco-friendly house and landscape called the Urban Ark 30 years ago, told me he used this approach to direct rainwater from his roof to the right spots in his vegetable garden, obviating the need for irrigation with purified drinking water. 

•    Plant a rain garden. This is a shallow depression, ideally at the lowest area of your yard, where water can collect and filter into the soil. Plants in the rain garden will soak up water and help purify it. Heavy soils may need to be amended with sand or gravel to make them drain faster in the rain garden; our sandy soil drains fast already.

A rain garden in Leeds, MA--photo U.S. Air Force

I like to think that we designed a rain garden without meaning to, because the land slopes down from the fence lines, making the center of the yard a collecting site for rainwater. I’d still plant a rain garden if I had a place for it. It’s a great excuse for a new planting project.

Gypsy moth: more complicated than you'd think

While waiting last week for my computer to return from urgent care, I contemplated a talk about biological controls by Joseph Elkinton, a professor of environmental conservation at the University of Massachusetts, that I heard last November. 

Gypsy moth caterpillar

    What Elkinton said about the history of gypsy moth in North America turns out to be unexpectedly relevant. We had a gypsy moth surge in 2016, and this year there has been significant defoliation by gypsy moth caterpillars, especially in southeastern Massachusetts.

Voracious gypsy moth caterpillars shred leaves

    A complicated web of factors influences the gypsy moth population. It all goes back to acorns.

    Gypsy moth (Lymantria dispar), native to Europe, was introduced to Medford, Massachusetts by Étienne Léopold Trouvelot, an astronomer dabbling in silk worm breeding. He thought he could cross the gypsy moths with native silk moths to produce silk in the US. The insects escaped from his home in the 1860s, and over 50 years they slowly established themselves in the wild. They’ve spread as far as Minnesota and North Carolina.

Life stages of the gypsy moth

    Elkinton explained that until 1989, gypsy moths experienced population outbreaks about every 10 years. Throughout the twentieth century, predator insects were introduced in hopes of controlling the gypsy moth population, but none did enough.

Predatory wasps kill caterpillars, but not enough

     Meanwhile, research into the ecology of the gypsy moth uncovered a system of natural controls. Robert Campbell of the US Forest Service found that the white-footed mouse was the most significant predator of the caterpillars, with birds less of a factor.

White-footed mouse, Peromyscus leucopus, in captivity

     Mouse populations rose and fell with the supply of their main food, acorns, which fluctuated with weather conditions. The mice couldn’t expand their population enough to control gypsy moth outbreaks, when caterpillar numbers spiked exponentially.

    Outbreaks were brought to an end by Nuclear Polyhedrosis Virus (NPV), which eventually killed up to 99 percent of the horde of larvae.

    This cycle continued until another accidental foreign introduction in 1989: Entomophaga maimaiga, a Japanese fungus. Infected by the fungus, gypsy moth caterpillars suddenly died all over southern New England.

    So with mice, viruses and fungi controlling its population, why is gypsy moth surging again? The levels of fungus are highest in wet years. Last year’s severe New England drought allowed the gypsy moth population to escape from its fungal control. This summer, caterpillars chomped foliage until June, when they started to die off. Caterpillars examined by Elkinton’s team showed a combination of viral and fungal infections. Wet weather had turned the tide.

    This means, thank heavens, that we don’t have to make the difficult decision whether to spray for gypsy moth.

    The future outlook for New England trees is mixed. Gypsy moths won’t die out completely, and our trees face a number of stresses from drought and other nonnative insect attacks. A tree can survive one defoliation, but repeated losses deplete its energy stores. Elkinton worries about major losses of native oaks, which the caterpillars particularly enjoy. Then what will happen to the white-footed mice?