Cover strawberries with straw for the winter

UNIVERSITY OF MINNESOTA EXTENSION - www.extension.umn.edu

Strawberry plants covered in leaves for the winter

Temperatures have been slightly above average for much of the fall, but it is finally time to cover your strawberries for winter. 

Before snow covers the ground, cover your strawberry patch with 2 to 3 inches of mulch. Both straw and leaf mulch work for this task. 

Also, insulate any container-grown strawberries or bring them to a protected area.

Apply the mulch once the strawberry plants have gone dormant. There are a few different rules-of-thumb you may use to determine when this should be.

• When soil temperatures are consistently below 40°F. This is the most common method that farmers use. However, most gardeners do not own a soil thermometer.
• Wait until daytime temperatures are consistently below freezing for at least 3 days.
• Do the plywood test:
  • Put a piece of plywood over a portion of your strawberry patch as a test for dormancy.
  • After three days, lift up the plywood.
  • If the plants under the plywood are still green after three days, they are dormant and ready to be covered with mulch.
  • If the plants turn yellow after three days, they are still actively growing and mulch should not be applied yet.

Types of mulch for strawberries

Both straw and chopped leaves may be used. 

Straw mulch is by far the more common choice for covering strawberries. Local garden centers and hardware stores often sell straw in rectangular bales for about $5-8 per bale. A rectangular bale is enough to create a 2-3 inch thick cover over a 10-foot-long row of strawberries. Straw may be harder to find in 2021 due to the summer’s drought.

If using leaves, it is best to mulch them with a lawnmower first. The smaller pieces tend to stay in place better than whole leaves. On the other hand, whole leaves create a more suitable habitat for overwintering beneficial insects like butterflies, according to the Xerxes Society. Two to three loosely packed wheelbarrows of mulched leaves cover about 12 square feet of strawberry plants at 2 inches deep. 

Why mulch strawberries?

Our Minnesota climate is too cold for strawberries to thrive from year to year without winter protection. If left uncovered, winter temperatures below 18-19°F will freeze and injure the dormant flower buds that produce fruit next summer. 

While snow may serve as a partial insulator, we shouldn’t rely on snow to protect the plants every year. Even a couple of inches of mulch over the strawberry plants in the winter is enough to protect the buds from the cold. 

If you are thinking, “I have never covered my strawberry plants in the winter, and they are just fine,” consider a couple of possibilities: 

• Your plants may have been getting injured, but you did not notice, or you attributed the low fruit production to something else. Winter-damaged strawberry patches do not die completely, but they have thinner canopies and less fruit.
• Secondly, perhaps the garden is in a warmer, protected area and avoided the cold temperatures characteristic of Minnesota winters.
• Third, your garden may have had enough snow cover to insulate the plants before mid-winter cold set in.

What to do with potted strawberry plants

Potted strawberry plants, along with their roots, must also be protected from winter temperatures. This makes protecting container plants a bit more complicated than in-ground plants.

• The first option is to move your container strawberry plants to an area that stays between 20° and 40°F all winter. For many gardeners, this space does not exist in our homes. In January and February, my garage gets well below 20°. So, most gardeners should consider insulating the roots and leaves with mulch or soil. 
• If the soil is not yet frozen and you have soil to dig into, you can dig a hole slightly wider than your container and place the container in the hole so that the strawberry leaves are just above ground level. Backfill the hole with soil around the container. Then cover the strawberry leaves with mulch.
• If you are unable to dig a hole for your container plants, then a third option is to mound several inches of potting mix or soil around the container in order to help insulate the roots. Then cover the strawberry leaves with mulch.

What if you cannot do any of these methods?

This might be the case if you garden on a balcony or rent your home. If your gardening situation prevents you from insulating container strawberry plants with these methods, consider growing day-neutral strawberries instead of June-bearing strawberries. Day-neutral varieties are meant to be grown as annuals rather than perennials, so you do not need to overwinter them. Plus, they produce fruit all season long!

Read more about growing day-neutral strawberries.