Warm days allow for treatment of magnolia scale

March is generally a good month to control insects such as magnolia scale with an application of dormant oil. Before pursuing any controls, verify that you have a problem insect. Avoid applying treatments just to make sure there will not be insects present.

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.

Dormant oils can be very effective with minimal impact on the environment when used properly.

• Propagate houseplants. Softwood cuttings, leaf cuttings, air-layering, cane cuttings and division may all be done in spring.

• Start seeds of warm-season annuals and vegetables in a moist, soilless seed 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. Adjust your start dates accordingly if frost-free dates are earlier or later where you live.

Transplant tiny seedlings into a “growing on” mix in slightly larger containers when they have two sets of true leaves. Gradually introduce the small plants to outdoor conditions before planting in the garden to acclimate them. They can be planted in containers or garden beds after the danger of frost has passed.

Tomatoes do not like cold weather and will have stunted growth when conditions are too cold, so plant them at a later date if the spring is cool.

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