November 1, 2026

When to cover plants for winter in your yard

Put winter mulch, burlap, and rose cones on after the ground has started to freeze, which usually follows a run of hard frosts in late fall. The first frost of the season comes too early. Seasonal cover keeps cold soil cold through winter, so it only works once the cold is already in the ground.

What winter cover does

A thick layer of mulch slows heat moving in and out of the soil. Bare soil thaws on a sunny afternoon and refreezes at night. Water in the soil expands each time it freezes, and the swelling lifts shallow roots and crowns toward the surface. There, wind and cold dry them out. Gardeners call this heaving. Mulch laid on frozen ground keeps it frozen through the warm afternoons, so the cycles stop.

Burlap and rose cones handle wind and sun. An evergreen keeps losing water through its leaves on a bright winter day, and roots in frozen soil can't replace it. A burlap screen blocks the wind and shades the foliage, which slows that loss. A rose cone shields the base of the plant, where grafted roses carry their graft. The cover is for nights like January 9, when our garden dropped to 3°F, the coldest reading of this year.

What goes wrong when you cover early

• Trapped heat. Mulch over warm soil holds that warmth in, and the plant keeps growing when it should be hardening off. Soft new growth dies on the first deep cold.
• Rodents. Voles and mice hunt for a dry, warm nest in late fall. A fresh mulch layer over unfrozen soil gives them one, right next to roots and bark they can eat.
• Rot. Wet mulch against a crown in mild weather holds moisture where fungi thrive. Perennial and strawberry crowns are prone to it.

Frozen soil slows fungal growth and leaves the plant time to finish hardening. Waiting costs you nothing, because a plant that has hardened off handles the early hard frosts on its own.

How to tell the hard freezes have arrived

A calendar date makes a poor trigger. Low ground and still air can push your yard below the forecast for your area. Cold air weighs more than warm air, so on a still night it slides downhill and collects in dips and hollows. Our own garden shows the gap. Published tables put our first frost at October 22. We logged our first fall frost on October 3, 19 days ahead of that. Against the forecast, our station runs 7°F colder. Published frost dates miss that kind of offset.

Every Siltwell garden gets frost alerts. At 5 pm local time each day, your microclimate offset is applied to the predicted lows covering the coming two days. If either adjusted figure lands at or below your threshold, which defaults to 32°F, a banner, a push, and an email go out. You can enter an offset under Settings, Garden, Edit garden. For a starting figure, try the microclimate checker, which sets readings from nearby home stations against the forecast.

The first alert of fall tells you to bring in tender crops. Leave the mulch bag closed. Watch for the stretch where alerts keep firing and the forecast lows sit well under your threshold. Suppose your alerts fire on five nights out of seven in mid-November, and the frost on the bed surface is still there at noon. That stretch is when to cover.

Frost alerts follow air temperature. They can't tell you whether your soil has frozen, because soil stores summer heat and freezes days or weeks after the air does. Before you spread mulch, push a trowel into the bed. If the top resists and lifts out in frozen crumbs, the ground is ready.

What to cover, in order

• Strawberries and shallow perennials. Straw or shredded leaves go over the crowns first, since heaving hurts shallow roots most. Our strawberry mulch guide covers depth and removal.
• Roses. Mound soil or set a cone once the plant is dormant and the hard freezes have begun. Vent cones on warm days so heat doesn't build inside.
• Evergreens. Water deeply before the ground locks up if fall was dry, then put up burlap screens on the windward side. Leave a gap so air moves around the foliage.

For the jobs that come before this, work through the fall order of chores by first frost. For which plants need cover at all, compare their limits with your yard's real winter lows.

In spring, pull the mulch back in stages as the alerts taper off. The same layer that kept the ground frozen will keep it cold after the air warms. We logged our final spring frost on April 30. With our offset applied, the effective date moves to May 20, so we uncover the beds slowly and keep the mulch close by.