Cardinals sing, maple buds swell, days brighten. With these first signs of spring comes that itch to clear away the dead leaves and decaying stalks of last year’s plants to make room for fresh green shoots.

But as I survey the general mess of my garden beds, I remember why I did not clean it up earlier: the National Wildlife Federation’s education mantra, “Leave the Leaves” in fall to sustain wildlife and pollinators, many of which are declining at alarming rates.

In addition to the goldfinches and other birds that feast on dried flower heads, “many moths, fireflies, butterflies and other beneficial insects overwinter in the soil or leaf litter in our gardens,” says Leslie Shad, Co-Lead Manager of Natural Habitat Evanston, a program of Citizens’ Greener Evanston.

“Their eggs and cocoons drop or are laid on the ground, and, with insect populations in steep decline, it is so important for us to help by leaving our leaf litter and not adding chemicals to the soil,” Ms. Shad says.

Insects have made the news lately because of downright scary reports from Germany and Puerto Rico that identified insect populations plummeting from 75% and 98% from the 1970s and 1980s. The New York Times called it the “Insect Apocalypse.”

Insects pollinate some 75% of food crops and 80% of wild plants, and they are the basis of the food web, feeding birds, mammals, fish, reptiles, amphibians and other insects. With insects already diminishing because of pesticides, the relentless destruction of meadows, forests and weedy patches, erratic temperatures and the drought-flood whiplash from climate change may be dealing the fatal blow. Biologist E. O. Wilson puts it bluntly: “If insects were to vanish, the environment would collapse into chaos.”

Dozens of insects visited my little wildflower oasis in the summer. By leaving the flower stalks and raking the fallen leaves into the beds as mulch last fall, I invited the bugs to stay for the winter. Though they are hunkered down out of sight, it is possible that the hollow stems are stacked inside with mason bees – highly valued in fruit orchards – and that the leaves shelter butterflies, moths, bees, fireflies, ladybugs and other beneficial insects at some phase of their lifecycle.

With spring on the wing, my homegrown pollinators may help pop my strawberry and serviceberry blossoms into delicious berries – unless I rake them all up and throw them in the waste bin.

“People view their yards as if they are their living rooms and must be kept pristine, with vacuumed lawns and not a speck of ‘dirt,’ but in fact they are living ecosystems,” says Tim Sonder, Co-Leader of Edible Evanston, the other garden-related program of Citizens’ Greener Evanston. “All that precious organic matter and the life it contains are needed.”

Earthworms have multiplied in my garden since I began saving the leaves, and their crumbly rich castings enrich the soil, while the leaves keep plant and tree roots moist and suppress weeds – impressive mulching services from this free and abundant resource from our own yards.

No wonder fox sparrows, Swainson’s thrushes and brown thrashers all stopped by to forage in the leaf litter last spring. “This kind of mulch will enhance and feed the soil better than anything you can buy,” Mr. Sonder adds.

Natural Habitat Evanston aims to support beneficial insects by encouraging gardeners to plant native shrubs, trees and wildflowers that sustain bugs throughout their lifecycle.

Ms. Shad and other Evanston gardeners, as well as schools and public gardens, have certified their spaces as National Wildlife Federation habitat, spreading the word that natural gardens provide sources of food, water, cover and places for wildlife to raise their young.

Evanston is now 96% of the way toward National Wildlife Federation-Certified Community Habitat status, lacking only 19 more gardens to certify Evanston as community habitat.  

Other Evanston residents are also taking action. Butterfly enthusiast Ryan Chew launched the Evanston Pearl Crescent Butterfly Project, encouraging gardeners to plant native asters, essential forage for Pearl Crescent caterpillars, which turn into small orange and black butterflies. “Even a small bit of habitat can help, whether you provide nectar from many species for the butterflies, or asters for caterpillars and a bit of winter cover of leaf litter around the asters to protect the caterpillars through the winter,” he says.

Mr. Chew recommends Smooth Blue Aster, Symphyotrichum laeve, and is offering free plants while supplies last. (Email habitat@naturalhabitatevanston.org.)

Even though some may still be itching to clean out the garden, horticulturist Jessica Walliser, author of “Attracting Beneficial Bugs to Your Garden: A Natural Approach to Pest Control,” recommends waiting until temperatures are consistently in the 50s or higher so overwintering bees and insects can warm up and re-emerge.

For anyone cleaning up earlier, she recommends these steps:

• Carefully cut down flower stalks. Place them loosely in an out-of-the-way spot or brush pile, or bundle together with jute twine. Hang or lean them against fence posts or trees. Insects will emerge when they are ready, and may return in summer to establish brood chambers.

• If you remove leaves, keep an eye out for eggs and cocoons. Eggs, larvae, pupae and adult butterflies such as mourning cloaks, commas and question marks (named after their punctuation-like wing spots) all nestle in the leaf litter. Move leaves to a tree bed or compost pile instead of shredding or discarding.

• Don’t add mulch until warm weather, to allow soil-burrowing insects, such as hummingbird clearwing moths, soldier beetles and many native bees time to emerge.

• Be vigilant for cocoons and chrysalises if pruning back woody perennials or shrubs. Leave them in place. “Some of our most beautiful moths and butterflies spend the winter in a delicate cocoon dangling from a branch, including the swallowtails, the sulfurs and spring azures,” Ms. Walliser writes.

• Anyone who looks for the smallest may be rewarded with the magic of fireflies, moths that look like hummingbirds and other fantastical and very ordinary bugs.

• Those wishing free native aster plants or seeds or information about how to certify the garden should email habitat@naturalhabitatevanston.org or go to nwf.org/certify.

• Those wishing to start their own pollinator garden should see Native Pollinator Garden Basics for the Chicago Region: https://westcook.wildones.org/2017/07/21/nativepollinatorbasics/.

• Native starter plants can be found online at prairiemoon.com. The 38-plant Garden Kits cover approximately 75 square feet and are designed with a diversity of 14 species of wildflowers and grasses for blooms spring through fall. Locally, such plants can be found at the Highland Garden Club of Evanston’s Backyard Botanicals sale on June 1 (9 a.m. – 3 p.m.) in Independence Park, Central Street at Stewart Avenue.