Autumn care tips for trees and shrubs

By Bonnie Orr
WSU Chelan/Douglas County Master Gardener

Bonnie Orr
Bonnie Orr – WSU Extension Chelan/Douglas County Master Gardener – photo by Don Seabrook, Wenatchee World

Fall is one of the best times to enhance your landscape with trees and shrubs. The temperatures are cooler, so plants can put more energy into creating roots.

When you place a tree or a shrub, consider root competition. It is a myth that trees have deep roots. Young seedlings send out a tap root for anchorage. But as the tree grows, the feeder roots spread out laterally. The roots of most trees and shrubs live in the top 12 inches of the soil.

Consider the placement of the tree or shrub in two manners: Will the full-sized plant interfere with current plantings or access to driveways or sidewalks? And will the growing plant’s roots compete with existing landscape features?

Not only will a tree shade out other plants, but its roots can grow more vigorously than smaller plants or the lawn.

The master gardeners often hear questions about lawn dying under trees. These plants do not do well in lawns. Lawn needs full sun and trees need full sun, so there is a conflict. The tree will trump the lawn. So consider a shade-loving ground cover in the space filling the tree’s drip line. It is best not to have turf growing right up to the base of the tree. Many trees die from a man-made injury called “whipper-blight,” when the cord from a string edger cuts into the young bark of the tree and essentially girdles it.

The autumn weather, and the arrival of precipitation and frost has changed in the last few years. The killing frost in our area seems to be arriving later into the fall. Young trees and shrubs need to be watered until the rains or snow fall. The roots will continue to grow until the soil temperature is 40 degrees. Even though the irrigation water is shut off in early October, water is still necessary for the growing roots. A water profile for roots should indicate that the soil is moist 8-12 inches deep.

Very young trees may need to have their trunks wrapped to prevent severe cold from causing the bark to break during freezing-and-thawing episodes. If the days are warm, the sap will flow through the tree, and a severe cold night will cause the sap to freeze, and the bark will be broken. This seriously harms the health of the tree. Broken bark usually is seen on the west and south sides of a young tree.

Young tree and shrub roots can be protected from severe frost with a 3-inch layer of mulch around the root area but not touching the trunk.

The precipitation in our area has diminished in the last few years. We are hovering in a drought with barely 6 inches of annual precipitation consisting of both rain and snow. A La Niña weather system is predicted for a third year in a row, which means that there will most likely be less precipitation in the fall and early winter.

Enjoy autumn.