Root, Root, Root For Healthy Tree Planning

By Laurie Casey
The Morton Arboretum

While Chicago baseball fans have the Fall Classic on their minds, others may be thinking about another fall classic...the incredible beauty of fall color, and how to get it by planting a tree successfully. Fall is a great time to plant most kinds of trees. We’ll cover the bases of tree planting here.

The trick is to create the right conditions for the roots. Up to 90 percent of the root system is removed when a young tree is harvested from the nursery and transplanted, according to Dr. Gary Watson, senior scientist at the Arboretum. “That gives you a perspective of what the tree needs to do in the first couple of years at its new site,” said Watson.

Start by digging the hole so roots end up at the proper depth, according to Watson. “Plant the tree, don’t bury it,” he said. Dig a shallow saucer-shaped hole with sides that slope up gradually. “The soil on the top of the root ball or container should be at ground level and not covered,” said Watson. (The flare at the bottom of the trunk should be visible.) Make the hole two to three times the diameter of the root ball. If the root ball is wrapped in wire or burlap, cut away as much of the restraint as possible.

Use existing soil to fill around the tree’s roots, advises Watson. The young tree must adapt to the soil in your yard to thrive. If your soil has a lot of clay, add at most 25 percent organic compost.

Mulch properly, which can help trees grow twice as fast, research shows. Spread 3-4 inches of double-ground mulch out to the drip line (area directly below the tips of branches). Pull mulch away from the trunk, creating a gulf, like a donut hole. Mulching helps insulate the soil from extreme temperatures, helps it retain moisture, and adds nutrients to the soil near the roots. Never pile up mulch against the trunk. While this kind of “volcano mulching” is common practice, it’s actually harmful. The bark can start to decay, inviting pests and disease.

The final step involves adequate watering. “People want to add nutrients to make a tree grow, but until a tree makes a good root system, water is the big issue,” said Watson. “The most important thing you can do is water where the roots are,” said Watson. In its first few months the tree gets its moisture from the root ball, which dries out quickly, within a day or two. Even if soil around the root ball is moist, the root ball may be dry, so check moisture often. Find more guidelines at www.mortonarb.org (choose “Plant Trees,” and then “Selection and Care”).

Hey! Hey! You’ve scored a healthy, beautiful new tree. Now, you’re ready to go. Or, if you want to pick out the kind of tree you’d like to plant for its fall color, visit the Arboretum and view the amazing array of trees from 40 countries, before heading to your favorite nursery.

Glad You Asked

Q. How can I tell if my soil has good drainage?
A. Young trees can drown when too much water gets trapped in the planting hole by compacted clay soil surrounding it. If you suspect a lot of clay, dig a one-foot-deep hole and fill it with water. If the soil has been dry, let it drain and refill. The water should drain in a few hours.

Q. Why shouldn’t I put fertilizer in the bottom of the planting hole?
A. Applying fertilizer at planting time gives few benefits, said Watson. Plus, undisturbed soil provides support from underneath. “Beginners want to make nice fluffy soil for those roots to grow down into, but as soon as you put a heavy root ball on top of it, the soil compacts and the hole becomes too deep,” said Watson.

At the Arboretum
Learn the top ten rules for using arbors, pergolas and other garden focal points at “Selecting and Using Garden Features,” 7-9 p.m., November 11. Fee, $32 (discount for members). Registration now open. Call (630) 725-2468.

Laurie Casey is a staff writer at The Morton Arboretum.