Applying a layer of mulch around the base of your perennials, rose bushes and shrubs is an important fall chore best done in late November or early December. Let me explain why it is so necessary.
When the ground freezes, it actually lifts the plants ever so slightly up from the ground. As the plant is lifted, a small amount of the roots break. If the ground stays frozen, this is no big deal. Come the spring, as the ground thaws, the plants drop back into their original position. The damaged roots have time to grow in the cool, moist soil of early spring. This is the plan, but it does not always work out the way we would like.
When the ground freezes in the winter, it can also thaw again if the weather turns mild. This allows the plant to drop back into the soil. However, if the ground keeps freezing and thawing, your plants will wind up with a lot of damage to the roots. Then, in the spring, the roots may not have time to repair before the weather warms. In extreme cases, the roots may be so badly damaged that the plant ultimately dies.
If you remember back to last winter’s mild weather and the alternate freezing and thawing of the soil, you now know why so many plants died this spring. If you could keep the soil frozen once it freezes, then you would have minimal damage to the roots. By applying a layer of additional mulch around the base of the plants, it will insulate the soil and allow it to ultimately stay frozen. Even if the temperatures fluctuate, the soil remains frozen. This protects the plants and they have a better chance of surviving the winter.
You can use bark mulch around the base of the plant. It should be spread out in a layer that is 3 inches deep. It doesn’t need to be spread over the entire perennial bed, but just where the roots of the plant are. The same applies to your trees and shrubs; the mulch needs to be 3 inches deep, extending out from the base of the plant and covering the soil where the root system is concentrated.