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

 

Insect superfoods

Visiting Coastal Maine Botanical Gardens this week brought some encouraging news about insect-friendly plantings. The designers had showcased many of the same flowers I’m growing to attract insect visitors, some inside the butterfly house near the entrance to the garden. Monarchs fluttered around this enclosed space, lighting on swamp milkweed and purple coneflowers. I spotted two species of caterpillars on stalks.

Monarch on purple coneflower in the butterfly house

   
    Planting for insects isn’t just for pollinators. It’s also intended to help leaf-eating insects, particularly caterpillars of moths and butterflies. 

Monarch caterpillar

Therefore Thomas Berger performed a useful service by cross-referencing lists of the best plants for these two purposes to derive a master list of insect “superfoods” posted by the Ecological Landscape Alliance. At the top of the section on herbaceous plants were goldenrods, asters, and sunflowers.

    Goldenrods support 11 species of specialist bees—bees that can only feed on a limited group of native flowers—and 115 kinds of lepidopteran caterpillars (caterpillars of butterflies and moths). Asters and sunflowers aren’t far behind. Goldenrods attract monarch butterflies and feed their caterpillars, making them second to milkweeds for supporting these fast-disappearing butterflies. 

    This is good news for my garden, because lots of goldenrods and asters are growing here already. I started some goldenrod from seed years ago. Patches of goldenrod here and there mark its spread around the yard. Unfortunately I didn’t keep a record of which species I’d planted. From photos, I suspect it was blue-stemmed goldenrod, Solidago caesia. Two years ago I bought some sweet goldenrod, Solidago odora, for a new perennial bed. Both native species have proven to be easy to grow and free-flowering.

    Goldenrods are members of the Compositae, also called Asteraceae, a useful family of plants because their central discs are made up many tiny flowers, each with pollen to offer. 

Visiting a daisy flower is an efficient way to collect pollen

The “petals” of the daisy-shaped blooms are actually strap-shaped flowers too. So an insect visiting one of these composite flowers gets lots of pollen with minimal travel. Goldenrod blooms are small, but if you look closely, you’ll see they share the family shape. 

Goldenrod's tiny daisy flowers

 

By the way, goldenrod doesn’t trigger hay fever. It has sticky pollen that doesn’t blow around like that of real culprits, such as ragweed.

    I’m growing some New England asters (Symphyotrichum novae-angliae) with pretty blue flowers. But aster volunteers are much more plentiful in the garden. In the past few years, a white-flowered type has popped up in lots of part-shaded spots with no effort on my part. I suspect it’s white wood aster, Eurybia divaricata.

Aster volunteers

    Last week I wrote about my bad luck growing sunflowers. I learned from Berger’s post that Helianthus annuus, the garden or field sunflower, was brought to New England by Native Americans as an agricultural crop and isn’t native here, although our local specialist bees can still use it. A native option is woodland sunflower, Helianthus divaricatus. Meanwhile, I’m growing oxeye sunflower, Heliopsis helianthoides, also called false sunflower, a different native genus but useful to pollinators too.

Oxeye sunflower