How to

Mulch strawberries for winter

The leaves have gone flat and red, and the hard freezes have started. Cover the bed with straw before the deep cold reaches the crowns.

Grown in Ohio, zone 6a. Your frost dates move the calendar; the signals don't. Broadfork goes by where your garden is, not its zone: frost dates for your ZIP code in the US, or the ones you type in anywhere else.

Four minutes to read. The steps stand on their own.

Before you start#

The straw isn't there to keep the soil warm. It stops the freezing and thawing that heaves crowns out of the ground to dry, and it keeps the hard cold off them.

Bare crowns are damaged or killed below 12 °F. The overwintering flower buds go sooner: the data puts the damage at 15 °F, or at 20.

Use clean straw: oat, wheat or soybean, free of weed seed. Soybean straw is usually weed-free and doesn't pack down. Chopped cornstalks work too, if you can get them.

Not leaves. Whole leaves mat into layers that hold water and leave room for ice, and they smother the plants. Grass clippings smother them too, and hay brings weeds.

Day-neutral plants are best not kept over winter. Kept anyway, they're lost at the same 12 °F, so they take the same straw.

The steps#

1. Wait for the plants to go dormant. The leaves flatten and turn red or gray. Until they do, leave the bed bare.
2. Let the cold harden them first. Short days alone carry them to about 25 °F, a frost hardens them fast, and steady cold finishes the job by early December. Covered too soon, they winter worse.
3. Go by the soil, not the calendar: 40 °F or colder, several days running. One version wants three days in a row at 40 °F or below; another adds three hard freezes; a third, several sharp freezes in the low 30s or high 20s.
4. Get it on before the air drops to 20 °F. Several nights near 20 °F is the warning; below it, the flower buds die. Most years the straw goes on between mid-November and mid-December.
5. Cover the plants 2 to 3 inches deep. Shake it out loose over the whole bed so no plant shows. Some of the data says 3 to 5 inches, settling to 2 to 4 over the winter.
6. On a raised bed or a strawberry pyramid, go 6 to 8 inches. Straw or chopped cornstalks, either one.

Short season Where winters are long and hard, one source waits for the ground to freeze before the straw goes on, later than the 40 °F rule.

In spring#

Pull the straw off the plants when they start to grow again: new leaves showing, or about a quarter of the plants with new growth. Don't wait for the leaves to yellow under it.

Or go by the soil again: off once the top 2 to 4 inches are above 40 °F.

Don't pull it early, either. Leave it on as long as you can; uncovered in March, the plants can bloom before the frost danger has passed.

Leave half an inch to an inch of straw over the plants. It holds down weeds, cuts disease and keeps the berries off the soil.

Rake the rest into the aisles, or beside the bed, and leave it there.

When a frost comes for the blossoms, rake it back over the plants. On early varieties like Earliglow, that can be the difference between a good crop and none.

If it goes wrong#

Covered too soon

The plants never finished hardening and take more winter injury. Next fall, wait for flat, red leaves and cold soil.

Crowns pushed up out of the soil

Freezing and thawing heaved them up to dry. That swing is what the straw is there to stop.

A matted, icy cover

Leaves. They hold water and ice against the plants. Use straw next time.

Weeds coming through

Hay, or straw with weed seed in it. Next time, clean straw.

Yellow leaves, rotting crowns

Left on too long. The plants starve and rot under it, and the berries come later and fewer. Pull it at the first new growth.

Frozen blossoms

Pulled too early, so the plants bloomed ahead of the last frost. Next spring, leave it on longer and keep the straw in the aisles to rake back on frost nights.

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