Today is the first day of fall, and with it come many garden tasks. Knowing which ones should be done now and which should wait until late winter or early spring is tricky. I recently asked Tim Kohlhauff, urban horticulture coordinator for Spokane County Extension, for some advice on the timing of these tasks.
“Make sure your trees and shrubs have plenty of water going into winter,” he said. “They continue to lose water through the winter – especially evergreens – so you want to make sure they’ve been well-watered before the soil freezes and they can’t absorb any more.”
Mulching is a great way to protect the roots of perennials, trees and shrubs. It keeps the soil moist and prevents freeze-thaw cycles that lead to frost heaving.
“While cleaning up your garden, it’s important to get rid of any diseased or insect- infested plant tissue,” Kohlhauff said. “This will reduce the number of pests in your yard and removes their shelter over the winter.”
He also mentioned that weeding the garden in the fall is an easy way to eliminate hosts for disease and insects, and saves time in the spring.
While Kohlhauff believes fall is a good time for planting trees and shrubs, he emphasized the importance of following some guidelines for the best success.
“Dig the planting hole wide and shallow and avoid amending the soil as this can form a border with native soil that is difficult for small roots to bridge,” he said. “Make sure the root flare (the wider area above the roots at the base of the trunk) is at soil level. Above all, don’t let the roots dry out before, during or after planting.”
“Fall is a great time to remove dead wood from woody plants, but for most trees and shrubs, it’s a good idea to wait for leaves to drop before doing any major pruning work,” Kohlhauff said. “That makes it easier to see the structure of the plant once the leaves are gone.”
Raspberry and blackberry canes that produced fruit this summer can be pruned down to the ground in the fall. There is an exception with fall-bearing varieties, however.
“Fall-bearing plants produce fruit at the ends of the current year’s canes and can produce another crop on the lower part of the cane the following summer,” he explained. “You can leave these canes alone if you’d rather have two crops of smaller berries but remember to cut them down after the second, summer crop. Otherwise, prune all canes down to the ground in the fall for one larger crop in late summer or early fall of the next year.”
Fruit trees should not be pruned until late winter or early spring.
Shrubs that bloom in the spring – lilacs, forsythia and cherries, for example – should only be pruned in early summer, right after they have finished blooming. Pruning them now will sacrifice some of next spring’s blooms.
Since summer-flowering trees and shrubs bloom from buds that are produced earlier that same year, pruning them in the fall won’t remove flower buds.
Kohlhauff clarified that while roses can be pruned in the spring or fall, fall pruning should be limited to the removal of taller rose canes that can be damaged from winter winds or bending beneath heavy snow.
He suggests dividing spring and summer-flowering perennials in the fall and dividing late summer and fall-blooming plants in the spring.
“This applies to woody plants as well,” he said. “Broad-leaf evergreens like rhododendrons have a hard enough time surviving our winters without adding transplant shock to the mix, so wait until spring to plant them.”