Reroute the roots to get new plants growing

May 17--Round and round the pot we go, and if we don't stop, the plant won't grow.

"Roots that circle inside the container are a common issue with the plants we buy in spring," says Sharon Yiesla, plant knowledge specialist at The Morton Arboretum in Lisle. It can be a problem with all container-grown plants, from cell-pack annuals to houseplants, perennials, shrubs and young trees.

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"Look into the holes at the bottom of the pot," Yiesla says. "If you can see a lot of white roots, the plant is pot-bound. If you see roots going horizontally, they are circling."

Roots try to grow outward, but if they're stopped by the sides of the pot, they turn and grow around the root ball inside the plastic. If you plant the root ball as is, the roots will stay on their circling course. They may never spread out to stabilize the plant and collect water and nutrients. That can keep the plant from thriving and even kill it.

Fortunately, there's an easy fix. "On a small plant such as a flower or vegetable transplant, just gently pull apart some of the fine roots at the bottom or sides of the root ball before you put the plant into the soil," Yiesla says. "Once you get them out of their rut, they'll grow out into the soil."

On plants with fleshy or woody roots, you may need to make some cuts in the outside of the root ball, using a sharp knife or pruners. New fine roots will grow from the cut surfaces. Without a pot to constrain them, they'll grow outward as they should.

When the Arboretum's staff plants shrubs or container-grown trees, they often use a more drastic technique. Using a sharp spade or knife, they slice off the outer inch or so of the root ball on all sides. That gets rid of any circling roots and provides plenty of places for new roots to sprout.

Plants sold in garden centers in spring often are heavily fertilized to make them look full, with plenty of flowers, to attract buyers. Heavy fertilizing also supercharges root growth, cramming the pot with roots until they are forced to circle.

All else being equal, it's best to choose plants that aren't pot-bound. If you do, Yiesla says, be sure to reroute the roots when you transplant them.

Beth Botts is a staff writer at The Morton Arboretum in Lisle (www.mortonarb.org).

For tree and plant advice, contact the Arboretum's Plant Clinic (630-719-2424).