November 1, 2007 at 8:09 a.m.
There is often confusion about when to add mulch. The best time is to wait until the ground begins to freeze. Sometimes that can be into mid-to late November. However, since many of us are under time constraints, we mulch when we find time. It is more important to get some insulation down than to worry about the critters that might burrow under the mulch.
If snow falls before the ground freezes, lay the mulch on top of the snow. Unless it's a really heavy snowfall, there is still a good chance it will melt off at some point, before the cold weather stays for the winter.
Snow is the best natural mulch provided to our plants. It is a good insulator that helps to hold the soils heat and prevents frigid air from infiltrating the soil. Bare soil loses heat, which allows the ground to freeze to greater depths. However, in the last few winters the snow has offered little protection for our plants. Whenever we had an adequate snowfall, it came too late in the season to protect plants.
How thick a mulch layer you apply in the fall depends on what you are using. Straw is the most effective winter mulch because it has hollow stems that trap air and insulates the soil the same way a down jacket holds your body warmth in. A depth of four to six inches should be sufficient. Straw is getting more difficult to get because fewer farmers raise oats, also, supply and demand makes it more expensive than some other mulches.
Speaking of straw, it is by far the best mulch for strawberries. Again, the hollow stems give it room to breathe while other mulches pack down the strawberries. This packing could affect the plants come spring.
Leaves can be effective mulch, especially because most of us have plenty of them. While straw mulch should have a four to six inch layer, leaves should have a 10 to 12inch layer. One of the best ways to use leaves is to bag them and pile the bags on top of the plants you want to protect. This method has been tested in the Duluth area on roses with good results.
It's a good idea to put shredded bark or wood chips around young or newly planted trees and shrubs. If you have done this in the past, check to see that the depth is about six inches. Remember to leave a little space around the trunk or stem so the bark can stay dry and not mold or rot.
When we think of annual flower beds, we often think about the small flowers. Don't forget that dahlias, glads, cannas, and sunflowers are also annuals. After they are dug, the soil should be treated much like that of a vegetable garden. Many gardeners mulch their small flowerbeds with compost, pine needles or straw after the flowers are well established. Clean out any vines and weeds and dig the mulch into the bed before the ground freezes.
Perennial gardens need to be treated differently. Clean out any weeds, and prune each accordingly. Depending upon which perennials we are talking about, mulch after the ground freezes with a four to six inch layer of loose mulch, such as straw, leaves, pine needles, compost, etc. Fall mulch is to keep the frost in, not to keep it out. The freeze/thaw process that often happens during late winter can expose the roots or crown of the plant. Spring winds can dry out the roots or crown resulting in the death of the plant.