A guide to planting trees that will leave you confident about survival, longevity

If the Arbor Day spirit moves you to plant a tree, plant it right to give it the best chance for a long life of spreading green branches and sheltering people and homes.

“How you plant a tree makes a critical difference in whether it will survive and how healthy it will be for the long term,” said Julie Janoski, Plant Clinic manager at The Morton Arboretum in Lisle. “The most important things you can do for a tree are to choose it carefully so it’s the right kind of tree for your site and to avoid planting it too deep.”

Here are some basics of proper tree planting:

Find the base of the trunk. To make sure your hole is the right depth, locate the base of the trunk, where it flares out into the big, anchoring roots. That spot is often buried in soil when you buy a tree, whether it comes in a pot or wrapped in burlap. “Dig down to find the first big roots, and remove all the soil above that point,” Janoski said. “Don’t just assume that the soil level in the pot is correct.”

Measure the root mass. You’ll need to know the depth, from the root flare to the bottom, and the width.

Dig a wide, shallow hole. It should be 2 to 3 times as wide as the root mass and shaped like a shallow soup bowl or saucer, with sloping sides.

“Tree roots grow out to the side, not down, and a wide hole makes space for them to push out horizontally,” Janoski said. “Even after you’ve refilled the hole, there will be a wide area of nice loose soil for new roots.”

Be careful not to dig too far down. “Planting too deeply is a major cause of long-term tree problems,” she said. The hole should be just deep enough so the flare at the base of the trunk will sit at the level of the surrounding soil, or slightly higher. For example, if the root mass is 11 inches deep, the hole should be just 10 or 11 inches deep at the center.

Gently place the tree in the hole. Avoid handling it by the trunk or branches; grasp it from the bottom of the root mass. Set it in the middle of the hole and check that it is at the right depth. Walk all around it to make sure the trunk is upright from all angles.

Remove as much wrapping as possible. If the tree came wrapped in burlap and wire, cut off and remove as much of it as you can reach.

“It’s OK to leave the wire and burlap underneath,” Janoski said. “They won’t interfere with roots growing out sideways.” Make sure to take off any tags, wires or ropes wrapped around the trunk or branches. They could cut into the bark as the trunk grows wider and eventually kill the tree.

Fill the hole. Use the same soil you removed. After filling the hole partway, gently but firmly tamp down the soil around the root mass to remove air pockets and keep the tree stable. Repeat, filling and tamping, until the hole is full. The soil level should be even from the base of the trunk out beyond the edge of the hole.

Water well. Pour 5 to 10 gallons of water gently onto the root mass.

Spread mulch. Make an even layer of mulch, such as shredded wood, in a wide circle around the base of the tree. It should be 2 to 4 inches deep.

“Don’t pile mulch too deeply, and be careful to keep it a couple of inches away from the base of the trunk,” Janoski said. “Mulch should never be in contact with the bark. It can trap moisture and lead to decay and disease.”

Make the mulch circle as wide as you can, to hold moisture in the soil, insulate the roots and protect the tree’s bark from damage by lawn mowers and other power tools.

Keep watering. For at least the next two years, you will need to water the tree on a regular basis.

“It doesn’t have enough roots yet to live on rainfall,” Janoski said. “It will need your help.”

At first, water right near the base where the root mass is. Over time, as the tree extends its roots, you’ll need to water a wider area.

“The best watering is long and slow, so the roots have time to absorb it,” she said. Use a soaker hose, a trickle from a hose or sprinkler or a bucket, pouring gently. “Don’t water every day,” she said. “Water deeply, and then wait several days before watering again.”

Arbor Day, the last Friday in April, is a traditional tree-planting day, but you can plant trees through June and again in September or October, avoiding only the hottest and driest part of summer. “There’s plenty of time to choose and plant a tree this year,” Janoski 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.