When you shop at the garden center, how do you know you’re getting a healthy plant?

“Don’t just judge by the green part you can see,” said Stephanie Adams, plant care pathologist at the Morton Arboretum in Lisle. “Look at the roots, which are just as important.”

Here are some tips from Adams for choosing good plants:

Read the label. “The first step is to make sure you’re buying the right kind of plant for where you’re going to put it,” she said. Consider how much sunlight the plant needs and make sure it is hardy in USDA plant hardiness zone 5, which applies to most of the Chicago area. If the plant is a tree or shrub, find out about its height and width to see if it will fit in the space you have. Make sure the plant is a good match to the soil conditions in your garden.

Judge the color. Most plants should be a uniform medium green. If a plant’s leaves are not uniformly green, make sure the white spots or purple tint are the appropriate color for that variety being grown and not a problem. Some cultivated varieties are bred to have different colored leaves. For example, a plant with yellowish leaves may have been grown this way, or it may be a naturally green plant that is losing chlorophyll due to disease. The label should clearly indicate what the plant is intended for.

Look for symmetry. Among perennials and shrubs, choose plants whose leaves and stems are evenly distributed all around.

Check for healthy roots. “Ask permission to gently remove the plant from its pot and examine the roots,” Adams said. “It’s common sense, like looking under the hood before buying a car.” In annuals, vegetables and most perennials, the roots should be white. The roots of trees and shrubs may be yellowish or brown. You should be able to see many roots spread throughout the soil. Roots and soil should be moist.

Avoid plants with diseased roots. “If you buy a plant with bad roots, you’re doomed,” Adams said. A sickly plant will disappoint you, and it can also introduce fungal spores or disease-causing bacteria into your garden soil, where they can infect other plants. “The diseased roots are usually brown, sometimes even black,” she said. “They may look spongy or flat, like a shoelace, because they’ve fallen apart.” Also avoid dried out roots.

Check the apartments on the spot. “When I buy a dish of plants, I usually pull out one or two plants from the middle to check for roots,” Adams said. “If any plants in the apartment look poor, either the leaves or the roots, I won’t buy them. A disease could spread throughout the apartment.

Too many roots? No problem. On a plant that you are going to transplant, it is not a problem if it looks bound to the pot, with roots that completely fill the pot, or if it has circular roots. “You can fix that when planting,” she said. For potted plants, make cuts around the outside of the root ball and ruffle the fine roots to encourage them to grow into the soil. For circular roots, cut or separate them to direct their growth outward into the soil. “The main roots should grow like the spokes of a wheel.”

Avoid potted houseplants and container plants. It is important to avoid buying a tied pot if you keep it in the same container. Or, transplant it to a larger pot so its roots aren’t overcrowded all summer.

Get a guarantee. For major purchases, such as trees and large shrubs, make sure the garden center gives you a written guarantee and be prepared to do your part. “The warranty will only protect you if you have planted and cared for the plant correctly,” Adams said. “It won’t cover a plant that dies because you forgot to water it.”

For advice on trees and plants, contact the Morton Arboretum Plant Clinic (630-719-2424, mortonarb.org/plant-clinic, or [email protected]). Beth Botts is an editor at the Arboretum.