Early spring in Chicago often brings spells of warm weather. But that doesn’t mean it’s time to start gardening, says Doris Taylor, Plant Clinic manager at The Morton Arboretum.
These strings of warm days are usually followed by the return of colder weather. Hard freezes are common in March, and the average date of the last frost date in the Chicago area is not until May 15.
A layer of mulch around trees and shrubs and in garden beds helps keep the soil cold during warm spells, so plants don’t come out of dormancy too early. Although we welcome the sight of early sprouts, like those at right, and even flowers, they can be damaged by a hard freeze.
Working in the garden at this time can damage the soil structure, Taylor says. Even if the soil is thawed at the surface, it probably still is frozen farther down. That prevents the soil from draining and keeps it wet.
When you walk on wet soil, your weight can pack the soil down so air and water can’t flow through it. That’s bad news for plants’ roots. Digging too early also can compact the soil.
There are some tasks you can do now in the garden, if you are careful not to walk on the soil, she says. Work when the ground is frozen, or make sure you stand on garden paths or stepping stones to distribute your weight.
Cover vulnerable sprouts. When below-freezing weather is predicted, cover the sprouts of spring bulbs and perennials with a lightweight mulch such as leaves.
Check for frost heave. Perennials, especially those planted within the last year or two, may be thrust out of the soil by the freeze-thaw cycles of late winter. Gently press the plants’ crowns back into the soil.
Cut back ornamental grasses. It’s best to get this done before the new growth starts.