Q: I have always planted shrubs, perennials and trees in the spring. My local big-box stores and my favorite nursery are having sales on new plants, not just old ones they are trying to dump. There is a "fall is for planting" sign. Is this just an advertising gimmick, or can I really add some new plants to my yard at this time? Will they be able to survive the winter?
A: I know a lot of gardeners who do all their planting in the spring, but fall can be a good time to plant. Large trees and shrubs can be planted until the ground is frozen. You are right to worry a bit about the winter weather for some small plants.
As fall weather arrives, the tops of plants begin to go dormant. The root systems often have a burst of growth because the soil cools off much more slowly than the air. This allows us to install plants with larger root systems in the fall without fear. The deeper roots of big plants will have a chance to grow out into the surrounding soil, helping establish the plant. Some trees will send out another burst of root growth in the early spring (even though the soil is cold) before their tops show signs of breaking dormancy. Fall-planted trees and shrubs have a head start on the same plants planted in the spring.
Small plants, such as perennials in small pots and ground cover vines, may have a problem when planted in the fall if the soil goes through multiple freeze-and-thaw cycles each winter. The small plants will not get many roots into the surrounding soil in the fall before the ground freezes. The soil from the pot surrounding the roots and the garden soil are often so different in composition and water holding ability that they freeze and thaw at different rates. They also expand and contract at different rates. This can push the small plants out of the ground, even if the plants are mulched properly.
If the soil rarely freezes or freezes and stays frozen, plants with small root systems can be planted in the fall if mulched properly. In cool climates, you can add the mulch when you plant. In cold climates, you should wait and add most of the mulch after the ground freezes so that the soil will be insulated and remain frozen.
Fall-planted trees and shrubs are dormant, but they still need to be watered. Keep the roots moist until the ground is frozen. Evergreens need to be protected from drying out. If they are being planted where the winter winds will blow, then they can be protected from drying out with anti-transpirant spray. CloudCover, Moisturin and Wilt-Pruf are readily available sprays that slow the amount of water lost in any plants installed in the fall.
The spray is applied after the plant is dormant and just before the winter weather is going to keep the ground frozen. The spray wears off over the winter, so plants don't need to be washed off in the spring. It can also be applied to Christmas trees and evergreen wreaths.
Jeff Rugg's weekly column, "A Greener View," can be found at creators.com.