Your deciduous trees and shrubs have lost their leaves and the perennials are standing but brown. So, here’s the answer to the title question. Mulch is a regulator. It moderates the temperature of the soil beneath it and regulates the rate at which moisture seeps into the soil. Organic mulch like wood chips provide the bonus benefit of returning essential nutrients to the soil as it decomposes. Inorganic mulches like stone chips are only decorative and don’t provide any environmental benefits.
While the above ground portions of your trees, shrubs and perennials may appear to be dead, they’re not. They’re dormant and the roots are still alive. I compare plant dormancy with animal hibernation. In each case, the organism is alive but functioning at a significantly slower pace. As a result, plant roots continue to benefit from the regulation that mulch supplies.
It could be argued that plants need winter mulch more than summer mulch. We recommend four inches of mulch in winter but only two, and under certain conditions three, inches during the growing season.
Mulch regulates the amount of water reaching your plant roots by absorbing some of the moisture from rain and melting snow and then releasing it into the soil over time. It moderates temperature by acting as insulation, protecting the roots from the freeze/thaw cycles that we experience every winter.
When spreading mulch, don’t pile it up the trunk in a mulch volcano. Mulch provides the perfect cover for small rodents like mice as they dine on tree and shrub bark. Also, mulch touching trunks releases its water on to the trunk, rather than into the soil. Any crack, cut or break in the bark can create a perfect environment for rot and other microbes.
I recommend double ground hardwood mulch because it’s made from recycled debris from tree trimming operations. Recycling this material contributes to plant health while reducing the stream of waste going to landfills.
If you spread four inches of mulch for the winter, don’t forget to remove an inch or two in the spring. Four inches is too thick for the growing season. Measure the mulch depth before removing any in spring. Some may have already decomposed.
You can buy bags of mulch at garden centers and home stores but that’s expensive, especially for large areas. We can deliver it in bulk much less expensively. We can either dump it in your driveway for you to spread or one of our professional landscape crews can spread it for you.