Margaret Lauterbach

Garden plants vital to the life of butterflies

Planting milkweed in your garden might help restore the monarch butterfly population.
Planting milkweed in your garden might help restore the monarch butterfly population. TNS

Most of us enjoy watching the “flying flowers” that some call butterflies or flutterbys visiting our flowers, but we’ve got to allow their offspring access to some of our garden plants if we want these beautiful creatures to survive. Vividly striped caterpillars feeding on parsley, carrots, Queen Anne’s lace or dill transform to black swallowtail butterflies after metamorphosis. They start life as tiny black caterpillars with a white saddle, then develop green rings around their bodies, and bright yellow splotches on the black rings. They’re hard to miss.

Yellow Tiger swallowtails are common here too, but they start life looking like a bird dropping, later they are smooth and green with blue spots, with a yellow ring near the prominent orange eye spots. We don’t often see them until they become butterflies since these caterpillars feed high in willow, poplar, cherry and birch trees.

And there are the popular monarch butterflies, those noble migratory butterflies. We keep reading their numbers are dropping because of the wide usage of pesticides in the United States and the reduction of the eastern monarchs’ wintering grounds in Mexico. Storms last winter killed millions of monarchs and toppled several of the monarchs’ favorite roosting trees. Their population now is about a 10th of what it was in 1996. Monarch butterflies west of the Rockies spend winters in warmer climes than ours, but the western monarchs overwinter principally near the Monterey Bay and San Diego areas in California

Pesticides meant for other insects or caterpillars take a hard toll on the monarch population. Only one part in a billion of clothianidin (a neonicotinoid pesticide) can have a bad effect, stunting and even killing monarch larvae, and that pesticide may appear via soil or seed. Neonicotinoids may also be conveyed via nectar, killing adult monarchs. These toxic substances have been found on “bee friendly” plants sold by the large chain stores that carry garden supplies. Another pesticide, BT (Bacillus thuringiensis) intended for corn earworms, may drop with pollen on milkweed, killing monarch larvae too.

Another cause of their decline is the diminishing supply of milkweed. Some don’t want that “weed” in their ornamental beds, others want roadside and vacant lot “weeds” sprayed with herbicide, weeds that often include milkweed. We’ve known for years that monarchs only lay eggs upon milkweed, for that’s the only plant their caterpillar offspring can eat. I have two volunteer milkweed plants in my yard that I’ve watched for several years, and have never seen a monarch interested in them. I suspect a small patch of milkweed would be more attractive to them than the isolated plants. Monarch caterpillars are vivid in color, with yellow, white and black rings around their bodies.

There are several varieties of milkweed, some native to Idaho. Among the natives, the swamp or pink milkweed requires abundant water, difficult in this valley. Antelope horns, or spider milkweed, thrives on drier soil, and the showy milkweed grows on fairly dry soil, but is intolerant of shade. Narrowleaf, or Mexican whorled milkweed, is another Idaho native that tolerates dry soil. Its leaves are narrow and whorled, and flowers are green and white with tinges of purple. The antelope horns milkweed blooms from May to October, the others all from June to September. Monarchs apparently like all milkweeds, but some gardeners also have noticed those butterflies on Buddleia flowers. They would be feeding on nectar there, not laying eggs.

Although we don’t see monarch butterflies here in large numbers, more may show up if some of us plant small patches of milkweed, just for them. The late teacher of fourth grade at Hawthorne and Cole schools in Boise, Faye Sutherland, introduced monarch butterfly culture to many students over the years, and she actively participated in monarch migratory research. In her classrooms, she raised monarchs from egg through caterpillar and metamorphosis stages, releasing tagged monarchs each fall.

At least some of those students still live in this area.

Make sure you’re buying the correct sun exposure variety of milkweed seeds for your site, and pay heed to the water requirements. Fall is the best time to plant milkweed, with winter giving the seeds the natural cold stratification they need for germination. A search on the Xerces society site shows no Idaho vendors of milkweed seeds, although there may be some. Nichols Garden Nursery, Albany, Ore., sells at least two varieties of milkweed seeds (varieties native to our area) plus a “monarch mix,” and Territorial Seed Co., south of Eugene, Ore., sells seeds for showy milkweed, also native here.

Send garden questions to or Gardening, The Statesman, P.O. Box 40, Boise, ID 83707.

Margaret will take a break

Starting in November, Statesman gardening columnist Margaret Lauterbach will take her two-month break. She’ll be back in January, just in time to start thinking about spring.