Program Specialist, Horticulture
Iowa State University Extension & Outreach
While it may seem a little odd to be dreaming of fresh strawberries on a cloudy, cool November day in Iowa, those delicious thoughts are an excellent incentive. To insure a bountiful crop next year, home gardeners need to mulch their strawberry plantings in the fall.
Cold winter temperatures and repeated freezing and thawing of the soil through the winter months are the main threats to the strawberry plants. Temperatures below 20 degrees F may kill flower buds and damage the roots and crowns of unmulched plants. Plants also can be destroyed by repeated freezing and thawing which can heave unmulched plants out of the soil.
Strawberries should be mulched in the fall before temperatures drop below 20 degrees F. However, allow the strawberry plants to harden or acclimate to cool fall temperatures before mulching the planting. Plants mulched before they have properly hardened are actually more subject 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.
Excellent mulching materials include clean, weed-free oat, wheat, or soybean straw. Chopped cornstalks are another possibility. The depth of the mulch should be three to five inches at application. The material should eventually settle to two to four inches.
In windy, exposed areas, straw mulches can be kept in place by placing boards or wire fencing over the area. The fencing can be held in place with bricks or other heavy objects.
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 material.
The winter mulch on strawberries should remain in place until plants show signs of growth in the spring. Do not remove the mulch in March. Early removal of the mulch may encourage plants to bloom before the danger of frost or freezing temperatures is past. A late frost or freeze could damage or destroy open flowers and substantially reduce yields. The first flowers are especially important as they produce the largest berries.
To determine when to remove the mulch, periodically examine the plants under the mulch during periods of warm weather in spring. Remove the mulch from the strawberry planting when about 25 percent of the plants are producing new growth. New growth will be white or yellow in color. If possible, the winter mulch on strawberries should remain until mid-April in central Iowa. When removing the mulch, rake the straw to the aisles between rows. If there is a threat of a frost late in the season during bloom, the mulch can be lightly raked back over the strawberry plants.
Although mulching strawberries isn't much fun, consider the tasty rewards. Strawberries and ice cream, strawberry shortcake, and strawberry cheesecake are a few of the rewards that await the dedicated gardener.