Dormant oil spray can be very effective to control magnolia scale

March is a good month to control insects such as magnolia scale with an application of dormant oil. Dormant oils can be very effective with minimal impact on the environment when used properly.

Verify you have a problem insect before pursuing any controls, and avoid applying unnecessary treatments. Temperatures should be at least 40 degrees with no chance of freezing or rain within the following 24 hours.

Avoid spraying on windy days to prevent any drift of the spray. As with any product, be sure to read the label to make sure the plants you are treating will not be damaged by the dormant oil spray.

• Prune fruit trees and grapevines as the worst of the winter cold is past and spring growth has not yet begun.

• It is OK to begin cutting back perennials, but make sure your beds are dry. You can damage the soil in the beds if you are walking around in them when the soil is too wet. Do your best to avoid walking on bulbs that are emerging, as the early warm weather has gotten some of them sprouting. Winter aconite and snowdrops are now in bloom at the Garden.

• Raspberries can grow into a tangled mess and produce poorly if not pruned properly. Prune fall-fruiting raspberries (fruit between August and October) back to ground now to produce one crop of fruit. Most fall-fruiting varieties are primocanes, which produce fruit in their first year of growth.

Cut the old canes as close to the ground as possible so that buds will break from below the surface of the soil. New canes will grow and set fruit later in the year. If the canes are not cut low enough, fruiting laterals may form on any remaining cane portion. These fruiting laterals will not be as healthy.

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