Two things that have been on our minds this August are drought and butterflies (and smoke and fires of course.) In my own garden, plants that have always seemed invincible are clearly showing the wear from this year’s high temperatures and lower than normal rainfall. And then a recent radio clip caught our attention with its report that warmer weather is bringing more swallowtail butterflies to the Pacific Northwest, but that many other butterfly species are struggling because of widespread habitat loss. That got us thinking about how to provide for butterflies with water-wise plants.
Why butterflies are in trouble
Butterflies largely depend on sun-loving plants, and in a region like the Willamette Valley many sunny spaces are taken up by cities, towns, and farms that lack the plants that butterflies need to survive. Even in wild areas, weeds such as the Himalayan blackberry or Canary reed grass out-compete native meadow plants that might otherwise support a healthy butterfly population. In addition to habitat loss, pesticides are hard on butterfly populations. Chemicals that are meant to target common pests such as corn ear worms also kill other types of moth and butterfly.
While habitat loss is a very large scale challenge, there is something immediate that individuals can do. Butterflies are among those species that actually can be helped by the plantings in our yards. One amazing example is found in the book Bringing Nature Home, where Doug Tallamy accounts that in Florida the believed-to-be-extinct Atala butterfly was inadvertently restored when their host plant, a type of cycad called a Coontie, became popular in residential landscapes.
What Butterflies Need
Butterflies start out as tiny caterpillars that need to eat the specific plants that their guts are adapted to ingesting. These plants are called larval host plants, and are almost exclusively native to the region where the butterflies exist. Once the caterpillars have grown, they need safe structures on which the larvae can build their chrysalis and transform into adult butterflies. As adults they feed on nectar from suitable flowers. They also need a spot of sun to warm themselves and dry out their new wings before they can fly, and a shallow bit of water or moist ground from which to drink.
Many people when thinking about butterflies immediately think of planting milkweed, and while native milkweeds are important butterfly plants they are only part of a much larger picture. Native trees and shrubs provide the vast majority of food for the caterpillars, and bunch grasses are important larval hosts and provide structure for eggs and pupae to shelter. Flowers from trees, shrubs, and small herbaceous species all provide nectar for the adults.
Plants for the Butterfly Garden
This easy native plant combination described below will work as a stand-alone composition or can be added piecemeal to your existing garden to increase butterfly habitat. All of these plants tolerate full sun, are naturally drought resistant, and will look good together. In combination, these plants are both host plants for the larva and nectar sources for the adults.
Tree: Oregon White Oak (Quercus garryana) Native oaks are host to a tremendous number of butterflies and moths, and they are beautiful stately trees that provide welcome shade on summer days. Simply put, native oaks and their associated plant communities support more biodiversity than any other type of tree in North America. But they are large. Click here for a handy guide to determine if you have a good site for a white oak.
If you simply can’t fit an oak, Scouler’s Willow or Douglas Hawthorne are great butterfly trees for smaller yards, though they both appreciate some summer water.
Shrub: Oceanspray (Holodiscus discolor) Oceanspray is a larval host to several native butterfly species, and its fluffy white flowers in June also provide nectar. As designers we love oceanspray for its interesting foliage and flower textures, and its amazing ability to thrive in just about any conditions – sun to shade, moist to dry. Oceanspray is also larval host to Lorquin’s Admiral, Pale Tiger Swallowtail, and the Spring Azure species.
Grass: Idaho fescue or Roemer’s fescue (Festuca idahoensis var. roemeri) These closely related native fescues develop deep and extensive root systems that hold the soil against erosion, and allow them to survive with no summer water. They provide a wonderful airy gray-blue texture to the plant border, and unlike some grasses will hold their foliage through the winter. Fescue is also larval host to many species of the Skipper butterfly.
Globe gilia (Gilia capitata) An annual that will self seed readily once established. Blue globe gilia flowers in mid spring and its fluffy flowers are a good nectar source for adult butterflies.
Western yarrow (Achillea millefolium) Yarrow is an extremely tough and adaptable perennial with evergreen foliage. Its white flowers provide nectar through the summer and into the fall. It is native to most of North America, but look for plants labeled ‘Western yarrow’ to avoid genotypes from other parts of the continent.
Pacific aster (Symphyotrichum chilense) At about 30” tall, Pacific aster is easier to fit into a garden than the similar Douglas aster (Symphyotrichum subspicatus), which can get to 4-5’ tall and spreads very aggressively. It’s lovely light purple flowers combine perfectly with grasses and goldenrod, and are an important late season nectar source for butterflies, bees, and other pollinators.
Meadow checkermallow (Sidalcea campestris) This plant features beautiful airy light pink flowers in late spring, and reaches as high as 5-6’, though the main leafy portion of the plant is only 12-18” tall. This is the most drought tolerant and readily available of the native checkermallows. Provides nectar and is a larval host to the West Coast Lady butterfly.
- Gardening for Butterflies, by the Xerces Society – https://xerces.org/books-butterfly-gardening/
- North American Butterfly Association list of Willamette Valley Butterfly Host Plants – http://www.naba.org/chapters/nabaes/btrfly-gdng2.html