Strawberries need protection from the cold winter temperatures. If strawberries are left unprotected, temperatures below 20 degrees Fahrenheit may kill the fruit buds and damage the plant's roots and crowns. For every 5 degrees drop in temperature, the damage becomes more severe. Also, alternate freezing and thawing of the soil during the winter may lift unprotected plants out of the soil and also cause damage. Mulch needs to be applied before the temperature drops below 20 degrees Fahrenheit. In central Iowa, early to mid-November is generally a good time to mulch strawberries. Mulching strawberries while the plant is still actively growing may actually increase winter injury. Allow the plants to harden - off properly by exposure to 2 or 3 hard freezes.
Suitable mulching materials for strawberries include clean, weed-free oat straw, soybean straw or chopped cornstalks. If cut before bloom, sudangrass is another good winter mulch. Tree leaves are not recommended as they tend to mat down and smoother the plants. Apply 3 to 5 inches of mulch. Eventually, the material will settle to 2 to 4 inches.
Leave the winter mulch on until approximately 25% of the plants show signs of growth in the spring. New growth will be white or yellow in color. The winter mulch on strawberries is normally removed in mid-April in central Iowa. Early removal of mulch may encourage the plants to grow and flower prematurely. A late frost could damage or destroy the blooms and substantially reduce the crop. Rake the mulch to the aisles between rows or to the edge of the strawberry bed. If there is a threat of frost during bloom, the mulch can be lightly raked back over the plants.
This article originally appeared in the September 13, 2002 issue, p. 117.
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