A tiger swallowtail on lantana. (Butterfly Habitat Garden)

Several readers have written to me complaining that the garden seems to be devoid of its grace note this summer — that is, the butterfly.

By this point in the growing season, the coneflowers and black-eyed Susans and other composites should be groaning under the weight of swallowtails, skippers and painted ladies. When it comes to lepidoptera, my garden is empty, too. Even the cabbage whites seem oddly thin on the ground.

So is this dearth real or imagined?

“Both,” said Jeffrey Glassberg, president of the North American Butterfly Association. Butterfly populations are highly sensitive to environmental conditions, and insect populations normally fluctuate greatly from year to year. This is distinct from long-term trends linked to problems such as habitat loss and pesticide use affecting the overall prospects of butterfly species.

“Every single day there are fewer butterflies in the United States than there were the day before,” said Glassberg, of Morristown, N.J. “Every time you take a meadow and turn it into a shopping center, you have decreased the world’s population of butterflies.”

Buckeye. (Butterfly Habitat Garden)

As for this year’s low numbers, they might be linked to the harsh winter, which caused major plant death in the Washington area. Some believe the cold, wet and delayed spring took its own toll on early broods of butterflies.

Michael Patterson of the Clearwater Nature Center in Clinton said that “we are seeing some tiger swallowtails and great spangled fritillaries,” but he has yet to see, say, a red admiral or any monarchs even though a milkweed garden has been planted for their use.

“I don’t have anything quantitative,” he said, “but it seems as if the populations are less than they were in the past.”

Jennifer Frye, an ecologist with the Maryland Department of Natural Resources, said she saw her first tiger swallowtail only last week. “Maybe the first brood was just small, but that doesn’t mean that the numbers won’t pick up as the summer progresses,” said Frye, who works for the department’s wildlife and heritage service on the Eastern Shore.

Monarchs are a special case because many of them migrate, and their numbers in overwintering Mexican forests have dropped precipitously in recent years. Much of this is attributed to the loss of habitat due to development and shifts in agricultural practices, including herbicide-tolerant, genetically modified row crops that have meant the eradication of sustaining stands of milkweed, the larval food plant. Although the migration as a phenomenon is threatened, the species is not in immediate peril.

The gardener can help by raising plants that butterflies need. “Unlike many things, it’s actually easy for someone to increase the world’s population of butterflies,” said Glassberg.

Nectar is only half the story, and many butterflies can get nectar from various sources. (Some of them sup from fallen fruit.) More important, perhaps, is the vegetation you provide for the caterpillars to munch on, because certain species are what we might call picky eaters.

After 20 years in one suburban garden, I have pretty much run out of room for more woody plants. If I lived in the country I would plant a hackberry or two, which grows into a large but not necessarily majestic shade tree, is prone to leaf galls and has little off-season ornament. But it is the host plant of the mourning cloak, which has to be one of the most handsome of our butterflies, and the earliest to appear. The hackberry tree also feeds the hackberry emperor butterfly, the tawny emperor and the odd-looking snout butterfly.

My imagined rural spread would also have whole orchards of pawpaw trees, which grow to the size of old pear trees and produce the largest fruit of any native tree, and one of the most delicious. The deciduous leaves are drooping and furrowed and resemble buckeye leaves. The foliage, moreover, is favored by the caterpillar of the zebra swallowtail, which is even prettier to my eyes than the tiger swallowtail. I was in Indian Head, Md., a month ago and saw many zebra swallowtails, which was a thrill.

At my community garden, the butterflies (and skippers) have been slow to appear this summer, but I am biding my time. One gardener is growing the stinging nettle, a plant some consider a weed and others an herb with a broad range of healing qualities.

Where I grew up, kids gave it a wide berth because we knew from the earliest age that brushing against that distinctive arrow-shaped, hairy and serrated leaf would induce, in sequence, pain, welts and a rash.

If you squeezed the leaf forcefully, it wouldn’t sting because you thwarted the poisoned hairs. Hence to take bold action is to “grasp the nettle.” Given the choice, I would much rather grasp the nettle than grab the bull by the horns. (So much could go wrong.)

My intent is to steal a piece of this nettle and grow it in a pot. Like mint, it spreads by runners and is a devil to eradicate once established, hence the container idea. On my imaginary country property, there would be hedgerows liberally planted with nettle. Why the nettle-mania? It is a host plant for many of the brush-footed butterfly species that remind me of the fluttering beauties of my childhood, the mourning cloak, the red admiral and the question mark, the closest we get around here to something resembling the lovely tortoiseshell butterfly.

I keep one plant of rue, which draws the larvae of the black swallowtail, though I have yet to see a caterpillar on it this year.

The loss of butterfly habitat is depressing, but it is uplifting to think that the gardener can make a difference.

If you want to get a sense of how you can help, visit the Smithsonian’s Butterfly Habitat Garden on the Mall between the Natural History Museum and, alas, the Ninth Street Tunnel. In a linear garden that is 400 feet long and 45 feet wide, horticulturists have planted 250 species of plants, most of them labeled, that either provide nectar for adult butterflies or leaves for caterpillars, or both. The garden is bright with flowers and color, with such things as ironweed, phlox, tithonias, lantanas, dahlias, pentas, salvias, Joe-Pye weed and the cup plant. Senna plants, coarse but interesting, feed sulphurs and yellows.

This garden is inspirational, but it is never a huge magnet for butterflies, perhaps because of its isolation or the incessant traffic next to it. It is still a great place to see late-season flowers, and the bees love it.

“It will be interesting to see if it picks up late in the season,” said James Gagliardi, the garden horticulturist. “I saw a gorgeous yellow swallowtail yesterday. It does give me hope.”