October 5, 2006 at 7:01 a.m.
Fall is the best time to fertilize your lawn. When you fertilize in late September or October, the top growth is minimal, but the roots are strengthened. This will help set the stage for a lush lawn next spring and summer. Another important lawn task is aeration. Aerating a lawn consists of extracting small plugs of soil. This is done to control thatch development and to reduce compacted soil. Oxygen is also more available to the roots after aeration. Aeration machines are available for rent at many garden centers.
Lawn mower blades can be lowered to two or three inches now. In summer, taller blades of grass provide the soil protection against heat and drought conditions. The grass can be cut shorter in autumn due to cooler temperatures and moisture. "Snow mold" occurs in some lawns in the spring, after the snow melts. This can be prevented by keeping your lawn shorter in late fall.
Planting trees and shrubs in the fall can be very advantageous. You can find terrific bargains at many garden centers and nurseries. Many centers prefer to sell their potted and balled-and-burlap stock in lieu of over-wintering it. The warm soil and cooler air temperatures help develop a healthier root system. There are fewer insects to bother you or your trees and shrubs! Therefore, there is overall less stress to the plants.
Remember to water newly-planted trees and shrubs liberally with approximately one to two inches of water at a time, until the soil freezes. This should be done once a week. It is far better to water deeply once a week than to water lightly every day or so.
Mulching should be added to your to-do list. The last several winters have not given our trees and plants the needed snow cover to insulate against temperature fluctuations. On many days, the temperature soars well into the 30s while plummeting into single digits at night.
Trees, shrubs and perennials will continue building their root system after a frost if you've mulched the base of the plant. Four to six inches of straw, shredded leaves or pines needles, or two to four inches of wood chips make for great mulching material. Be sure not to use unshredded leaves as they tend to mat down and provide little insulation.
Minnesota's harsh winter climate can cause severe damage to trees. Sun scald is characterized by cracked areas of dead bark, usually on the south or southwest side of a tree. During the day, the sun can heat up bark to the point where activity is stimulated. When the temperature drops rapidly after the sun sets, the active tissue is killed. Young trees and thin-barked trees (maple, cherry, plum, crabapple) are most susceptible to sun scald. Older trees have thicker bark which insulates dormant tissue from the sun's heat. Sun scald can be prevented by wrapping the tree with light-colored material or plastic tree guards. The light color reflects the sunlight.
Some gardeners cut back the foliage on perennials in autumn to reduce fungal-leaf diseases in spring. Others prefer to leave the foliage to add winter interest. Ornamental grasses, succulents and wildflowers, among others, do add an interesting texture to an otherwise dull landscape, even when they're dry and brown.
If you decide not to cut back your perennials now, be sure to do it before growth starts in the spring. You'll have less of a mess and can still prevent diseases.
Lastly, remember to help the birds by cleaning out bluebird houses and bird feeders! This will prevent mold, the spread of diseases and insect infestations. Dump out any old seed and add fresh seed after the feeder is washed and dried. Many birds spend the winters here and will patronize your feeding stations if they're filled. Cardinals, chickadees and nuthatches are a welcome sight all winter long!
You can leave a question for a volunteer Master Gardener at 651-674-4417.
Depending on the volume of calls, they try to respond within a couple of days. During office hours ask for the Master Gardener voicemail, after hours, select ext. 18.
You can also get your question answered on the web at: www.extension.umn.edu/askmg.