Making Wise Plant Choices, Part 2: Keystone Plants

Climate-Conscious Gardening

Join Master Gardeners in the Arlington/Alexandria unit of Virginia Cooperative Extension in a series of monthly articles in 2021 as we explore the topic of climate change and practical actions individuals can take in their home landscapes in response. 

by Elaine Mills, Extension Master Gardener
Photos by Elaine Mills unless otherwise indicated

Home with purple cone flowers, oak leaf hydrangeas and wooden fence.

In Part 1 of this article, we explained the importance of adding native plants to home gardens, not only to widen the palette of landscape choices but to provide critical support to our local populations of beneficial insects and birds. Studies have shown that the particular selections gardeners make can have a tremendous impact on the diversity of life in our yards. Years of observations and research by University of Delaware entomologist Dr. Douglas Tallamy and his assistants have revealed that certain species of native plants, which he terms “keystone plants,” are especially supportive of a garden’s food web. Their foliage serves as nourishment for the larval stage of Lepidoptera (butterflies, moths, and skippers), and these caterpillars, in turn, are important components in the diets of many animals, including the young of most birds.

Chart of 20 most valuable woody and perennial native plant genera
Doug Tallamy’s chart of keystone plants]

Among the woody plants in the Mid-Atlantic region, members of the genus Quercus are by far the most supportive, hosting 534 Lepidoptera species. While the majestic white oak (Quercus alba), red oak (Quercus rubra), or willow oak (Quercus phellos) may be too large for some properties, the dwarf chestnut oak (Quercus prinoides) can be grown as a large shrub or small tree. It produces acorns when only five feet tall, within three to five years.

The genera of keystone trees tied for second position are Prunus (cherry) and Salix (willow), each hosting 456 Lepidoptera. Black cherry (Prunus serotina) may grow as tall as 60 feet, but it can be pruned and kept at shrub size if it is cut to the ground every 2 to 3 years. American wild plum (Prunus americana) and chokecherry (Prunus virginiana) can be grown as small trees or allowed to form thickets, offering cover and fruit to various wildlife. Homeowners should be aware that while the ripe fruit of Prunus species (minus the seeds) is edible by humans either fresh or cooked, all other plant parts contain toxic cyanogenic compounds that may cause death if consumed.

Black willow (Salix nigra), a 30- to 60-foot-tall tree, is generally not recommended for residential landscapes, but examples of understory to shrub-size willows are pussy willow (Salix discolor) and silky willow (Salix sericea). These plants require consistently moist to wet soil and do best when sited near streams or ponds. See the chart above for other top-rated woody plants.

Among native herbaceous plants, the genera most beneficial for Lepidoptera are Solidago (goldenrods), Aster/Symphyotrichum (asters), and Helianthus (sunflowers), which support 115, 112, and 73 species of butterflies and moths respectively.These plants also provide outstanding support to pollinators and birds. Goldenrods, which are often mistakenly confused with allergy-causing ragweed, can add touches of bright color to the fall garden while offering important late-season nectar and pollen to pollinators. The Plant NoVA Natives campaign’s guide lists seven locally native species, including blue-stemmed (Solidago caesia), gray (S. nemoralis), and rough-stemmed goldenrod (S. rugosa).

 

There are many native asters from woodland species such as white wood aster (Eurybia divaricata) and blue wood aster (Symphyotrichum cordifolium) to shrubby aromatic aster (S. oblongifolium) and tall New England aster and New York aster (S. novae-angliae and S. novi-belgii).

Native sunflower species, including woodland sunflower (Helianthus divaricatus), thin-leaved sunflower (H. decapetalus), and narrow-leaved sunflower (H. angustifolius) are all tall, reaching 5 to 7 feet or more and are best used in gardens where they can be allowed to spread.

Other top-performing perennials include bonesets and joe-pye-weeds in the Eupatorium genus, sedges, lupines, violets, geraniums, and black-eyed Susans. Look for an upcoming public education presentation on keystone plants early in 2022.


References

  • “Dr. Doug Tallamy and the Nature of Oaks.” May 15, 2021. The Native Plant Podcast, with Alonso Abugattas.
  • “Native Plant Finder,” National Wildlife Federation. [Best plants by zip code for supporting Lepidoptera, based on research by Dr. Doug Tallamy.]
  • Tallamy, Douglas W. Bringing Nature Home: How You Can Sustain Wildlife with Native Plants, Timber Press, 2009.
  • Tallamy, Douglas W. “Keystone Plants.” Notes, Pennsylvania Native Plant Society, Spring 2019.
  • Tallamy, Douglas W. The Nature of Oaks: The Rich Ecology of Our Most Essential Native Trees, Timber Press, 2021.
This entry was posted in MG in the Garden. Bookmark the permalink.