What's the best time to plant trees and shrubs, spring or fall? The short answer is "it depends," according to Sharon Yiesla, plant knowledge specialist at The Morton Arboretum in Lisle.
Spring is an obvious time, since most homeowners are active in the garden now anyway. They're amending and sowing vegetable beds, dividing and planting perennials, and reseeding the lawn. The garden centers and nurseries are full of shrubs and trees. Most new gardens are installed in spring, it's logical to plant the trees and shrubs first, and there's usually abundant rain.
"Spring is a great time for tree planting, but we have to choose a good day to ensure success," Yiesla says. It can be hard to find a good weekend for tree planting during the rainiest season of the year. "You don't want to dig a big hole when the soil is wet," she says.
If rain-soaked soil keeps you from planting until late May or June, a tree or large shrub may have a harder time getting established before the hot weather of July and August threatens it with drought.
The alternative is to wait until late summer or early autumn. "Most trees also do well if they're planted in the fall, as long as you don't leave it too late," Yiesla says. "If you wait until November or December, plants are more likely to fail."
Still, spring planting is better for some kinds of trees, usually because they are slow growers that need all season to establish roots before the soil freezes. Most evergreens are in this category, as well as bald-cypress, American hornbeam, ginkgo, larch, magnolia, hemlock, sweetgum, tuliptree and willow.
"In general, plants with shallow, fibrous root systems can be planted more easily in the fall than those with fewer, larger roots," Yiesla says. Whenever you plant, you'll need to remember to water often until the ground freezes. This is especially true if you need to plant a tree or shrub between mid-June and late August, when it's hot and often dry. "We don't recommend planting during the summer," Yiesla says, "but if you must plant then, watering is crucial."
How to Plant a Tree or Shrub
To plant a tree or shrub, dig a wide hole, the same depth as the root ball, so the plant doesn't sit too low. Cut or spread out any circling roots. Refill the hole with the same soil you removed. Water the tree thoroughly. Spread 3 to 4 inches of mulch in a wide circle over its roots, keeping the mulch a few inches away from the trunk. Come back and check the soil moisture every day or two for the first few weeks to see if water is needed. Then water every week or so for the rest of the year, unless it has rained a lot.
"No matter when you plant a tree," Yiesla says, "failure is most likely if you plant it too deep or you forget to water it."