So you want to beautify your landscape, improve your community, or celebrate Arbor Day by planting a tree. What could go wrong?
Quite a bit, if you make some common mistakes, according to an expert at The Morton Arboretum, the tree-focused public garden in Lisle.
“Proper planting is critical,” said Trinity Pierce, who has overseen the planting of thousands of trees as stewardship manager of the Arboretum’s Chicago Region Trees Initiative. “Taking time to do it right can mean decades more life for your tree.”
Here are some common tree-planting mistakes to avoid. For step-by-step advice, see mortonarb.org/how-to-plant-a-tree.
Digging a hole that’s too deep. A tree that is planted too far down, with its roots and part of its trunk buried too far in the soil, will weaken and may fail. Mere inches make a big difference. The planting hole needs to be just deep enough so that the root flare sits at or above the level of the surrounding soil. What’s the root flare? “It’s not quite trunk and it’s not quite roots,” Pierce said. “It’s that transition zone.” Before you dig, find the root flare — it may be buried several inches deep in soil in the pot — and measure from the flare to the bottom of the ball of soil and roots. Dig your hole just that deep in the center and no deeper. Once you have the tree in the hole, use the long handle of your shovel or rake to double-check that the root flare is at or slightly above soil level. “It’s much better to plant a little too high than too deep,” she said. As it grows, the tree will become heavier and settle into the soil.
Not making the hole wide enough. “Don’t try to jam a tree into a too-small hole,” Pierce said. Tree roots grow out sideways, and the newly planted tree needs an area of loosened soil where it can push out its roots to get started. Make your hole at least twice as wide as the tree’s root ball; three times is better. The hole should not have straight sides like a bucket; they can block the roots’ growth. Instead, make the sides gently sloped, like those of a wide, shallow pasta bowl.
Ignoring roots that circle. When you take a tree out of the pot, check for roots growing around the outside of the root ball. “That means the plant ran out of space and it’s just been growing in circles,” she said. Before planting, liberate those roots so they leave their circular path. Gently pull on the thin, fibrous roots to free them until the outer layer of roots is loose and fuzzy. If you encounter a thick, stiff circling root, cut it with sharp, clean pruners. New fibrous roots will grow outward from the cut end.
Pruning when you plant. Although trees sometimes need to be pruned to remove broken branches or improve their structure, pruning also creates openings for pests and diseases. Avoid pruning newly planted trees, which are already stressed. “Handle these plants with gentle loving care,” she said. Once the tree is established, in a year or so, you can prune it for shape.
Forgetting to water. After you refill the hole, pour two or three buckets full of water gently onto the root ball. “The tree is probably stressed from transportation and growing in a pot,” she said. “It may not have been watered. It needs your help.” Continue to water the tree frequently — about once a week, or more in dry weather — for two to three years, while the tree gradually extends its roots into a network that can collect enough water from the soil. “It’s going to take time for the tree to get established,” she said.
Piling mulch against the tree. “Mulch is a wonderful thing, but not if it’s piled up against the tree bark,” she said. That can lead to rot and can keep air from reaching the tree’s roots. Instead, spread the mulch around the tree in a wide, flat layer no more than 4 inches deep and keep it a couple of inches away from the bark.
Choosing the wrong kind of tree for your site. Different tree species need different conditions, and a tree that isn’t a good match for your site won’t do well no matter how carefully you plant it. For example, a tree that needs full sun will struggle in shade, and a tree that needs well-drained soil will fail in a wet site. “Take your time and choose carefully,” Pierce said. The Arboretum’s Search Trees and Plants tool (mortonarb.org/search-trees-and-plants) can help you research your options. “Find a tree that will not just survive but thrive,” she said.
For tree and plant advice, contact the Plant Clinic at The Morton Arboretum (630-719-2424, mortonarb.org/plant-clinic, or plantclinic@mortonarb.org). Beth Botts is a staff writer at the Arboretum.
