Apply Winter Mulch Now

Marginally cold-hardy plants
can be completely covered
with loose mulch materials.

There are a few factors to consider when setting up your favorite plants to survive the coming winter weather. 

One important factor is whether the plants can handle the winter weather in your area’s USDA cold hardiness zone. In Oklahoma, for example, there are three cold hardiness zones. The southeast part of the state is zone 7b, the panhandle and Miami are zone 6a, but, Tulsa is 7a and Bartlesville is 6b.

There are also microclimates on your property. For example, the south side of the house is warm enough to protect a wider range of perennials than the north side. Containers on a west-facing porch are more sheltered than containers out in the middle of a bed.

For the most part, plants that are native to your USDA growing zone (www.plants.usda.gov/) will do better no matter how harsh the winter is. But, as we have seen, drought with record cold temperatures can change everything.

Applying winter mulch will help hedge your bets, preventing wind damage, soil heaving from freeze and thaw, or drought drying of roots. In addition, the plants we love that are not quite cold hardy in our zone benefit from receiving an extra level of care.

Newly planted perennials such as trees and shrubs must be protected for the winter if you want them to perform at their best next spring.

Do not fertilize or prune once freezing weather has arrived. The new growth you stimulate will make the entire plant vulnerable to cold, dry, weather. Weak and diseased plants should be removed on sunny days that allow working outside.

Evergreens suffer the most during a winter drought. If there is no rain for a few weeks, water the plants in your garden that retain their color in winter. This is especially true of young evergreens.

When your area has had a killing frost (4 hours of 32-degrees F), it is time to apply mulch around perennials you want to thrive next year, including those in containers.

Mulch should be applied 6 to 8 inches away from trunks and ground-hugging stems. The volcano shaped mulch you often see hugging tree trunks can become home to insects, mice and other creatures that eat bark during the winter.

Mulches can be made of pine needles, tree bark, compost, cotton seed hulls, cotton burr, straw, sawdust, pecan shells, or grass clippings. These are called organic mulch. Non-organic or synthetic mulch materials, such as shredded rubber, can be used although they do not add anything to improving the soil over time.

Large mulch particles such as tree bark and pecan shells allow rain to enter the soil. Sawdust, grass clippings, cotton seed hulls and compost insulate the ground better but rain cannot sink down as well.

Two inches of fine compost is plenty while 5 inches of straw is necessary to provide the same freeze protection.

Do not use leaves unless they were shredded in the mower or previously composted. Never use leaves or stems from diseased plants in your compost or as mulch.

Organic mulches break down over the winter, improving the soil, increasing its ability to hold moisture, and supporting beneficial insects next growing season.

Roses benefit from being winter-mulched with a pile of loose material stacked taller than the graft. For example if the graft is 6 inches above the soil line, the mulch should be 8 inches tall.

Marginally cold-hardy plants in our area, such as gardenias, camellias, rhododendrons, canna lily and calla lily benefit from being completely covered by loose mulch. In the photo our gardenias are covered with pine straw.

In Oklahoma it is recommended that you remove mulch around the first of March. 

See OSU HLA-6404 for more details.