While you wait for autumn leaves to fall, consider planting a tree. “If you plant a tree in early autumn, the soil will still be warm enough to encourage root growth for at least two months,” said Sharon Yiesla, plant knowledge specialist at The Morton Arboretum in Lisle. “Growing roots is the most important thing for a new tree.” Plan to get a tree in the ground before mid-October to give the roots time to grow before the soil freezes. While they grow, you’ll need to water. Watering has become even more critical for new trees as the weather has become increasingly volatile and unpredictable, with a chance of hot spells in September or even October. “We can’t depend on autumn being rainy with gradually cooling temperatures, like we once assumed it would be,” Yiesla said. Fall planting agrees with most kinds of trees, such as buckeye, catalpa, crabapple, hackberry, hawthorn, honey locust, elm, Kentucky coffee tree, linden, maple, oak, sycamore, pine and spruce. “Some trees take longer to get established, so they are better planted in spring,” she said. They include bald cypress, American hornbeam, ginkgo, larch, magnolia, hemlock, sweetgum, tuliptree and willow. Broad-leaved evergreens such as rhododendrons are best left for spring too. Most do-it-yourselfers will plant younger trees that were grown in pots, rather than larger field-grown trees with their roots wrapped in burlap. Yiesla said that the container-grown tree, which has its entire root system in the pot, is a better bet for fall planting. “A balled and burlapped tree loses most of its root system when it is dug up from the field, and it needs a long time to regrow those roots,” she said. “It’s better to plant those trees in spring to give them more time.” When you are ready to plant your tree, “the most critical thing is not to plant it too deep,” Yiesla said. That can cause serious and even fatal problems years later. To avoid planting too deeply, locate the root flare — the place where the trunk flares out into the big anchoring roots, the way your neck flares out into your shoulder. That flare should sit right at the level of the surrounding soil and no deeper. “The root flare may be buried in several inches of soil in the pot when you buy the plant,” she said. Dig down to find the first fat roots growing out sideways; that’s the root flare. Remove all soil above that point. Measure from the root flare to the bottom of the root ball and dig a hole that is no deeper than that measurement. Make the hole wide — at least twice or three times as wide as the tree’s root ball. “A wide hole with sloped sides gives the roots elbow room to grow out sideways and anchor the tree,” Yiesla said. After you remove the plant from the pot and place it in the hole, doublecheck that the root flare is at or a little above the level of the edge of the hole. Refill the hole with the soil you removed and gently tamp it down around the tree’s roots. Learn more about tree planting at mortonarb.org/plant-clinic. Water the tree thoroughly using at least 10 to 15 gallons of water. Then spread mulch in an even layer around the tree, no more than 4 inches deep, in a wide circle. The mulch will not only insulate the tree’s roots from fall hot spells, but keep the soil beneath it warmer after the air turns cold, so the roots can keep growing. “Don’t pile the mulch up against the tree’s trunk,” she said. That may cause the bark to rot. It also defeats the purpose of mulch, which is only effective when it’s spread out in contact with the soil. Water the tree regularly until the ground freezes, which may be deep into December. “The roots will keep growing even when the tree has lost its leaves and appears dormant,” Yiesla said. “More root growth gives the tree the best chance to thrive next spring.” For tree and plant advice, contact the Plant Clinic at The Morton Arboretum (630-719-2424, mortonarb.org/plant-clinic, or [email protected]). Beth Botts is a staff writer at the Arboretum.