SI Gardening

The ideal time to fertilize trees is in the late fall, soon after leaves have dropped. This includes evergreen species as well. For complete information, see the November issue of The Green Thumb.

Weekly Garden Column

Winter Mulch Protects Strawberries
Tony Bratsch, horticulture educator
University of Illinois Extension

Depending on variety, strawberries have varying tolerance to cold. Lack of acclimation or “hardening” in the fall, as well as wide temperature swings, can decrease cold tolerance and increase winter injury to crowns. Research has shown that temperatures in the low teens can kill a high percentage of uncovered or poorly hardened plants.

Mulching helps to insulate plants from low temperatures and quick changes. Mulching also protects plants from drying winter winds which desiccate, or dry out the plants, especially when soil moisture becomes low or less available in frozen soils.

Strawberries are also shallow and somewhat brittle-rooted. Alternate freezing and thawing (frost heaving) of the soil in winter and early spring can damage roots. A layer of straw on the surface moderates this soil movement.

Strawberries grow and develop late into the fall months and should not be covered too early. They respond to low temperatures and moderate frost by gradually becoming more hardy and tolerant of cold. Signs of this tolerance include a “flattened” appearance, lack of any new leaves and red coloration of older leaves.

Apply mulch after plants have had time to acclimate and develop hardiness. Based on various studies, data indicates when soil temperatures at a 4-inch depth have reached and stay at 40 degrees F, straw should be applied. Soil temperatures can be checked with a simple thermometer. Another rule of thumb is to apply mulch after several 20-degree freezes have occurred. For most of Illinois, this usually happens between mid-November and mid-December, depending on location.

About any type of loose organic material can be used as mulch, but straw is the most readily accessible and it has good insulation ability. Avoid materials that contain weed seeds, such as hay, as well as sawdust or chips that are too heavy and dense. Apply a 2- to 3-inch straw layer, and for raised beds with greater exposure, apply several more inches. As the winter progresses, snow helps add even greater insulation, so leave it on the plants.

Straw should be removed in the spring when new leaf growth becomes evident in the center of the plant. Using a leaf rake, drag the straw to the edge of the bed to provide a cushion for developing berries, or into the walkway, and leave some on top to filter down between plants.

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