One of the best blanket covers to protect the crown and roots of the perennials, fruit crops and woody ornamentals from fluctuating temperatures is the use of winter mulch.

Contrary to popular belief that winter mulch protects the ground from freezing and offers warmth to the plant, winter mulch prevents the soil around the root zone area from freezing and thawing conditions. Repeated freezing and thawing of the ground occur when there is little or no snow cover in winter months. This forces the plant roots and crown to heave out of the soil and makes it vulnerable to cold temperature injury.

One of the common winter mulches is straw as it provides good insulation, allows sufficient air movement, lacks in weed seeds (if it is a clean straw) and does not smother the plant like a mat. A bale of straw can easily cover 100 square feet to at least 3 inches deep. Other winter mulches that can be used are bark chips, hay (may contain weed seeds), chopped corn stalks, pine needles, and shredded leaves and lawn clippings.

Typically, winter mulch is applied when the ground is about to freeze and thus it provides a buffering effect from fluctuating temperature. However, its hard to predict when the ground is about to freeze in fall and winter months. Hence its best to apply winter mulch in late fall season close to thanksgiving weekend or just before the first snow shower, whichever comes first.

Herbaceous perennials including ornamental grasses can be left unpruned and mulched around the crown to about 6 to 8 inches. The dead stalks of the perennials can add extra protection to the crown of the plant.

Unprotected strawberry plants can suffer a greater damage if the temperature drops to 18F. To mulch strawberries, use straw, marsh hay or sudan grass to about 2-4 inches deep.

To protect the rotos of newly planted (within last 5 years) or marginally hardy woody ornamentals and tree fruit crops (peaches, cherries), mulch over its root zone area with wood chips to about 6 inches deep. Be sure to wrap the trunk of the tree with hardware cloth (1/4 inch mesh) to protect from rodent attack. In mid – late spring, reduce the mulch to about 2-3 inches deep and keep the mulch 6 inches away from the tree trunk. If there are any soil cracks near the root zone area, fill it with soil.

Hybrid tea roses need a double layer of winter protection. When the temperature drops below 20F for at least couple of nights, mound the canes with potting soil to a height of 8-10”. Cut off the tall canes to about 30-36” above the ground and tie the cane tips together using soft twine. When the mounded soil has frozen, add a 12” layer of leaf or straw mulch on top of the mound and wrap the shrub with hardware cloth.

For garden inquiries, please contact our plant health advising office at 608-298-6945 and leave a voicemail. You can also email us at planthealth.advisors@extension.wisc.edu.