It’s time to think about protecting strawberry plants from the winter elements. Horticulturists with Iowa State University Extension and Outreach explain how to properly mulch strawberries to provide protection against winter injury. To have additional yard and garden questions answered, contact Hortline at hortline@iastate.edu or 515-294-3108.

Why is it necessary to mulch strawberries in fall?  

Strawberries should be mulched in fall to prevent winter injury. The main threats to the strawberry plants are low winter temperatures and repeated freezing and thawing of the soil through the winter months. 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.  

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. Apply the mulch after the strawberry plants have been exposed to several nights with temperatures in the low to mid-twenties. In northern Iowa, early November is usually the proper time to mulch strawberries. The proper time to mulch strawberry plantings in central and southern Iowa is normally 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 three to five inches of material. After settling, the mulch layer should be two to four 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 actually damage plants due to excess moisture trapped under the matted leaves.

How do I overwinter strawberry plants growing in a strawberry jar?  

Strawberry plants growing in a strawberry jar or other container will likely be seriously damaged or destroyed if left outdoors in winter. One option is to place the container in a cool location, such as an attached, unheated garage, in November. A second option would be to discard the strawberry plants in fall, dump out the potting soil, store the container indoors in winter and replant in spring. Day-neutral strawberries perform well as an annual crop.