Yard and Garden: Properly Mulch Strawberries for Winter


November 5, 2014, 11:38 am | Richard Jauron, Greg Wallace

While winter is not growing season for strawberries, taking care of strawberry plants remains vitally important. Before winter arrives, mulch strawberries to protect them, so they’re ready to grow in the spring.

Here are some tips from Iowa State University Extension and Outreach horticulturists on the ins and outs about mulching strawberries for winter. To have additional questions answered, contact the ISU Hortline at 515-294-3108 or hortline@iastate.edu.

Should strawberries be mulched in fall?

Strawberries should be mulched in fall to prevent winter injury. Low temperatures and repeated freezing and thawing of the soil through the winter months are the main threats to strawberry plants. Temperatures below 20 degrees Fahrenheit may kill flower buds and damage the roots and crowns of unmulched plants. Repeated freezing and thawing of the soil can heave plants out of the ground, severely damaging or destroying the plants.

Wintercare Strawberries

When should I mulch my strawberries?

Allow the strawberry plants to harden or acclimate to cool fall temperatures before mulching the planting. Applying mulch before the strawberry plants have properly hardened may make the plants more susceptible to winter injury. In northern Iowa, strawberries are normally mulched in early November. Gardeners in central and southern Iowa should mulch their strawberry plantings in mid-November and late November, respectively.

What materials are suitable for mulching strawberries?

Excellent mulching materials include clean, weed-free oat, wheat or soybean straw. Chopped cornstalks are another possibility. Apply approximately 3 to 5 inches of material. After settling, the mulch layer should be 2 to 4 inches thick.  
 
In windy, exposed areas, straw mulches can be kept in place by laying wire or plastic fencing over the mulch. The fencing can be held in place with bricks or other heavy objects.

Are leaves a suitable mulch for strawberries?

Leaves are not a good winter mulch for strawberries. Leaves can mat together in layers, trapping air and creating space for ice to form. The leaf, air and ice layers do not provide adequate protection. A leaf mulch may damage plants due to excess moisture trapped under the matted leaves.

When should I remove the mulch on my strawberries?

To reduce the chances of crop damage from a late frost or freeze, leave the mulch on as long as possible. Removing the mulch in March may encourage the plants to bloom before the danger of frost is past. A temperature of 32 F or lower may severely damage or destroy open flowers. Since the first flowers produce the largest berries, a late spring frost or freeze can drastically reduce yields.  

To determine when to remove the mulch, periodically examine the strawberry plants in spring. Remove the mulch from the strawberry plants when approximately 25 percent of the plants are producing new growth. New growth will be white or yellow in color.  (If possible, the winter mulch should remain on strawberries until mid-April in central Iowa. The average date of the last 32 F temperature in spring occurs in late April in central Iowa.)  When removing the mulch, rake the material to the aisles between rows or an area next to the planting. If there is a threat of a frost or freeze later in the season during bloom, lightly rake the mulch over the strawberry plants.  

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