Food for thought

 This week my garden club got together on Zoom to watch a video of a talk by Doug Tallamy. I’ve been a Tallamy follower since 2011, when his book Bringing Nature Home changed my gardening philosophy. Since then I’ve been working on growing more native plants.

 

Insectary bed: flowers and foliage for pollinators and other insects

    In 2019 Tallamy published a new, more prescriptive book, Nature’s Best Hope. He’s marshaling us to rescue biodiversity by creating Homegrown National Park, a combined nationwide habitat for native insects in our backyards. 

    Tallamy demonstrates how we can get the most environmental bang from our native plantings by prioritizing caterpillar host plants. Caterpillars provide the lion’s share of the biomass birds need to feed their young. 

Hummingbirds feeding insects to their chick

Tallamy has identified more than 800 caterpillar species on his 10-acre property in Pennsylvania as he and his wife have replaced nonnative invasive plants with natives (check out his stunning photos of some of them in the new book).

    A light bulb went on for me when Tallamy mentioned that people occasionally write him to point out that an imported species—the Asian ginkgo tree (Ginkgo biloba), for example--used to be native to North America in a previous geological era and claim it’s therefore entitled to native plant status. That doesn’t matter, he said. What’s important is whether a plant supports any native insects. Ginkgoes don’t.

 

Ginkgo is a beautiful tree from Asia-photo Sunroofguy

 
    We’ve come a long way since concern about supporting insects first surfaced. I remember reading in the 1980s about designing a butterfly garden. That was when we planted butterfly bush (Buddleia spp.), which is now out of favor because it’s nonnative and potentially invasive. Butterfly bush and many other flowering imports do serve a purpose, though, providing nectar for bees, butterflies and moths in their adult forms.

Eastern Tiger swallowtail nectaring on a butterfly bush

    As I became more aware of my garden as an ecosystem, I started planting native flowers that provide the right pollen for native pollinators, especially bees. Now we can take the next step and choose to plant for native caterpillars. These aren’t looking for flowers. While adult pollinators can afford to sip nectar unselectively, caterpillars need to eat the right leaves to be able to grow and pupate.

      Because of decades of research in this area, we now know that about 90 percent of insects specialize: they’ve evolved to live off a limited group of plants. Most caterpillars aren’t equipped to deal with the chemical defenses mounted by plant species outside their small group of native host plants.

 

Monarch caterpillars need to eat milkweed

 
    So with data accumulating about which plants host which native insects, we can stop fighting about whether gardeners should plant only native plants. Instead, we can ask which plants host the most insects. Tallamy proposes that we prioritize keystone plants, such as native oaks, willows, cherries, and goldenrods, that provide food for hundreds of species of native caterpillars. How to find these? You can go to the websites of the National Wildlife Federation and the Audubon Society and get lists for your zip code. Somehow this prescription seems much more doable.

 

Native red oak supports more insects than any other local tree-photo Jason Hollinger

 

Making themselves at home

This August I’m keeping an eye on native plants I’ve recently added to the garden. I have to admit that not every native I’ve brought home has settled in easily. But an inventory of the newish plantings under the shade of our dawn redwood (Metasequoia glyptostroboides) shows that some are chugging along.

Before recent additions: shade-tolerant plants under the dawn redwood

    I have high hopes for New York ironweed (Vernonia noveboracensis). This will grow to a shrub-sized perennial, up to 6 feet high and 4 feet wide, with purple flowers in late summer and fall. 

New York ironweed blooming last fall

Doug Tallamy’s Bringing Nature Home web site notes that ironweed is a caterpillar host plant for 18 species of moths and butterflies in my area. So far it’s only about a foot tall, but it has pleasing feathery foliage. When the sheet composting area decomposes enough for planting, I might move the ironweed forward away from the tree, since it grows in sun in the wild.

    I love the dark reddish-brown flowers of Carolina allspice (Calycanthus floridus), a beetle-pollinated magnolia relative also known by the common name of sweetshrub for its flowers’ fruity scent. 

Carolina allspice flowering in Central Park

I first planted this shrub in significant shade next to a Japanese stewartia (Stewartia pseudocamellia). It has survived and flowered, but it’s not making many branches. When we took down the hemlocks near the dawn redwood, a sunnier patch opened up. I took the opportunity to try Carolina allspice again.

    Another native shrub that seems to be thriving is coastal doghobble (Leucothoe axillaris). Its best feature is its low, arching sprays of shiny leaves. Native plant expert William Cullina explains that the common name describes the tangled thickets leucothoe creates in the wild that even a dog can’t wriggle through.

Shiny foliage of coastal doghobble

     Leucothoe is often recommended with other broadleaf evergreens for foundation plantings. I inherited lots of those: rhododendrons (Rhododendron spp.), mountain laurels (Kalmia latifolia), and Japanese pieris (Pieris japonica), but I’d never grown leucothoe until I realized it was a native that might do well under the shade of the dawn redwood, and so it has. Those leaves are still shiny and pristine in August, which is more than I can say for most of the foliage in the yard. I haven’t seen any flowers yet. They’re going to be little dangling white bells.

    By the way, neither Carolina allspice nor the leucothoe is actually native in the Northeast. They’re both from the Southeast, but since they can grow here, I’ve decided to give them a try. We each get to decide how native our natives are going to be. If I were a true purist, I’d restrict myself to plants from my ecoregion, the Boston Basin. So far I’m not willing to be that exact.

The Boston Basin is my ecoregion

    A true New England native is already established next to the dawn redwood: winterberry (Ilex verticillata). This has grown into a small double-stemmed tree and produces masses of red berries that birds eat during the fall and winter. I’m glad to know that it also provides caterpillar forage for 42 moth and butterfly species.

Winterberry fruit in late fall