Start preparing your houseplants for spring

As houseplants begin their new growth, you should prune them and start fertilizing them. Cut off any spent flowers or dead leaves or branches and any yellowing leaves. Remove the dust from the leaves with a spray of water from a spray bottle or by gently wiping them off with a moist cloth.

As the sun strengthens in spring, some plants — like African violets — may need to be moved farther away from a south-facing window to avoid leaf scorch. Rotate your houseplants regularly, so each side receives an even amount of light for more uniform growth and a balanced shape.

This is a good time to repot houseplants if needed. If you see white roots through the holes in the pot's bottom, the plant may be pot-bound and in need of more space.

A white or yellowish crust near the drain holes of the pot or at the base of the pot indicates a buildup of salts from either fertilizer or hard water. Excess salts in the growing medium can damage plants, causing brown leaf tips and margins. To flush out the salts, drench the soil thoroughly with water. Do this outside if it is not too cold, or in your kitchen sink.

Start seeds of warm-season annuals and vegetables indoors, under lights in a moist, soilless seed-starting mix. These seeds should be started six to eight weeks before the last spring frost date, which is May 15 at the Chicago Botanic Garden in Glencoe. Adjust your start dates if the normal frost-free date is earlier or later where you live.

After the seeds have germinated and the tiny seedlings have two true sets of leaves, transplant them into slightly larger containers with a good potting mix. The small plants may be planted in the garden after the danger of frost is past. First, however, gradually introduce them to outdoor conditions by placing them outdoors for increasing amounts of time each day for a week or so.

Tomatoes do not like cold weather at all, so it is best plant them later if the spring seems too cool.

• Tim Johnson is director of horticulture at Chicago Botanic Garden, chicagobotanic.org.