From this cold, spring bloooms will burst — so be ready

It may be cold out there, but late winter is the time when plants are getting ready for spring. Be alert to the earliest signs in the garden and start preparing for the growing season by sowing seeds indoors.

General garden care

During unseasonably warm periods in late winter, early bulbs may sprout prematurely, especially those planted with a southern exposure close to a house or garage. The Chicago Botanic Garden in Glencoe has on occasion had snowdrops in flower in late February in similar locations. Leaves show first, with flower buds appearing much later. Subsequent cold weather might damage the edges of the above-ground foliage, but unless the flower bud has appeared, the cold will not affect the future flowering or health of the bulb.

A few small early bulbs can tolerate a bit of frost. They include winter aconite and glory-of-the-snow as well as snowdrops.

Keep watering any evergreens that are planted in containers outside, especially when temperatures are warm and conditions are dry. Evergreens continue to lose water through their leaves during winter.

Check garden beds to be sure plants have not been heaved out of the ground by the freeze-thaw-freeze cycles that are typical in late February. Gently press the crowns of perennials back into the ground, but avoid compacting the soil by stomping heavily around plants. Apply a layer of mulch to help prevent additional frost heaving.

Winter is a good time to prune trees and shrubs. Overgrown deciduous woody shrubs can be heavily pruned this month and next to rejuvenate them. Start by removing all dead wood. Prune old canes off at ground level, leaving several young canes. You may need to cut back the young growth if it is spindly.

If there are not any young canes, cut the large canes back to 2 to 3 feet from the ground. This will be unsightly, but if the plants are healthy, extensive new growth should start from the old canes in spring and fill in the plant. Shrubs such as lilacs that formed flower buds last summer will not bloom when pruned aggressively in winter.

Branches with buds for interesting foliage or spring flowers can be forced indoors. Prune branches that are not essential to the plant’s basic shape or save branches from your winter pruning. Branches should be at least 1 foot long and full of fat flower or leaf buds and should be cut on a day when the temperature is above freezing. Cut the ends at an angle and put the branches in water in a cool room out of direct sunlight. When the buds color up or the foliage begins to unfurl, arrange the branches in a vase and display them, but keep them cool and out of the sun.

Good choices for forcing this month include serviceberry (Amelanchier), magnolia (Magnolia), flowering quince (Chaenomeles), forsythia (Forsythia), crab apple or apple (Malus), flowering pear (Pyrus), flowering cherry (Prunus), spring-flowering witch hazel (Hamamelis vernalis) and redbud (Cercis).

Annuals

It’s not too soon to start annuals that get off to a slow start, such as pansies, violas, petunias, snapdragons and lobelia. While garden centers offer some favorites, the choices are seemingly endless when your grow your own, and the quantity will be too if you save all the little seedlings.

Use grow lights to ensure success. A florescent fixture hung on a chain works best, as you can adjust the level to keep the light at the optimum 8 to 12 inches above the seedlings. Providing bottom heat for the seedlings will also improve results. Heat mats or cables can be purchased at your local garden center.

Thin seedlings as needed, especially after the first set of leaves form, to prevent overcrowding and keep only the best plants. Remember to sow a few extras, but not too many.

Indoor plants

To keep Valentine’s Day cut flowers fresh, protect them from freezing temperatures outside and place them in room-temperature water as soon as possible. With a sharp knife or pruners, remove a minimum of 1 inch from each stem with an angled cut. Ideally, make this cut while the stem is under water. Cutting on an angle increases the surface area for water intake.

Add floral preservative to the vase water. Most preservatives contain an acid (to neutralize alkaline tap water) and an ingredient to discourage bacteria. Remove all foliage below water level so it does not rot.

Cut flowers prefer a cool, humid environment and should be kept out of bright light and away from heating vents. Do not place cut flowers close to a bowl of fruit or vegetables, since the ethylene gas emitted by ripening fruit can damage the flowers. So can cigarette smoke.

If healthy cut roses suddenly develop drooping heads, it may be due to air bubbles trapped in their stems. Float the entire stem in a sink full of warm water. Trim another inch from the stem, cutting on an angle below water level, and keep the cut end under water for at least half an hour. Meanwhile, try to gently straighten the drooping flower head as the flower and stem float. When the flower heads harden to a straightened position, the roses may be placed back in the vase.

Ÿ Tim Johnson is director of horticulture at the Chicago Botanic Garden (chicagobotanic.org).