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posted: 3/8/2014 6:00 AM

Give a head start to summer-blooming bulbs, tubers

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  • When sowing seeds indoors, keep pots in a warm place until growth appears, then move to a sunny location.

    When sowing seeds indoors, keep pots in a warm place until growth appears, then move to a sunny location.

By Tim Johnson, Chicago Botanic Garden

Give summer-blooming bulbs and tubers a head start by potting them up indoors in moist, soilless potting mix. Among the tender bulbs that make a good summer show are caladiums, elephant ears (Colocassia), tuberous begonias (Begonia x tuberhybrida), montbretia (Crocosmia), lily of the Nile (Agapanthus), garden cannas (Canna x generalis), tuberoses (Polianthes) and peacock orchids (Acidanthera).

Keep the pots in a warm place until new growth appears. Then move them into a sunny window or under grow lights if necessary. When all danger of frost has passed in May, gradually introduce these plants to the growing conditions outdoors.

Spring also is the time to propagate houseplants through softwood cuttings, leaf cuttings, air-layering, cane cuttings, or division.

Start seeds of warm-season annuals and vegetables in a moist, sterile 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 accordingly if the frost free-date is earlier or later where you live.

When they have two sets of true leaves, transplant the tiny seedlings into a soilless potting mix in slightly larger containers.

After the frost-free date, gradually acclimate the transplants plants to outdoor conditions before planting them outdoors into containers or garden beds.

Tomatoes do not like cold weather and their growth will be stunted when conditions are too cold. If the spring is cool, wait a couple of extra weeks to plant tomatoes outdoors.

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.

First, however, verify that you have a problem insect before using any controls. Avoid applying treatments just to make sure there will not be insects present. A good garden center or the plant information service of the botanic garden ( can help identify a pest problem.

When you apply dormant oil, 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 onto other plants. 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.

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

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