Do I Need Mulch Around a Tree in Freezing Temperatures?

Brush heavy snow off limbs with a broom to prevent breakage.

Mulches benefit trees and other ornamental plants all year by reducing weed growth, conserving moisture and regulating soil temperatures. Organic mulches -- such as straw, wood chips, grass clippings or cocoa hulls -- even improve the soil as they decompose. Mulches are especially important in the winter to protect trees from freezing weather.

Benefits

Organic mulches, such as wood chips and shredded bark, act as an insulator, regulating soil temperatures to avoid wide fluctuations. Mulches reduce moisture loss and can protect tree roots in freezing weather. Mulches also reduce heaving, which is caused by frequent thaw and freeze cycles and can dislodge a tree's roots from the soil.

Considerations

Mulch is almost always beneficial but may not be necessary to protect established hardy trees. Young trees, however, that are still establishing root growth especially benefit from mulch in freezing weather, as do half-hardy tree varieties.

Warnings

Apply 6 to 8 inches of mulch around the base of the tree, but do not mound the mulch so it rests against the trunk of the tree. Doing so reduces oxygen to the tree's roots, promoting disease or even killing the tree. Mulches may also harbor mice or voles during the winter, and they might feed on the tree bark if mulch is placed too closely. Although trees benefit from a mulch year-round, apply heavy mulch after the ground is frozen.

Additional Protection

In addition to a mulch, several other factors determine a tree's ability to withstand harsh winters. Plant trees adapted to your climate for best growth. Prune out winter-damaged branches to avoid infections or damage to the tree. Plant fruit trees and other vulnerable trees in full sun on a slight slope so frost pockets drain away quickly. Paint trees with white latex paint to avoid sun scald, if necessary. This condition usually occurs on the south or southwest sides of young trees and is caused by bright, white light reflecting off the snow followed by freezing nights. Trees with thin bark, such as cherry trees, are most susceptible. Water trees once a month during dry winter conditions.

References

• University of Minnesota Extension; Protecting Trees and Shrubs; Bert T. Swanson, et al.; 2011
• Cornell University Extension; Winter Protection of Trees and Shrubs; 2011

Resources

• University of Vermont Extension; Winter Protection; Leonard Perry, et al.