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Saving tender perennials through winter for next year's garden
Planter's Palette
By Diana Stoll | Columnist

You can save this coleus to enjoy next year.

 

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Published: 10/2/2010 12:01 AM

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After a long hot summer, most of us cherish the cooler temperatures of fall. We even look forward to that first mosquito-killing frost. Many trees, shrubs and perennials need the cooler temperatures to gently persuade them to prepare for their winter rest outside.

Tender perennials, however, begin to suffer with the first cool nights. If we do not bring them in from the cold, they will die. There are several methods to overwinter tender perennials inside. Some can be grown as houseplants; some prefer to go dormant in a cool, dark place; and others need their dormant bulbs, corms or tubers stored.

Grown as houseplants

Prepare plants you plan to keep as houseplants. Move them to a shady spot for a couple weeks before their big move to get them ready for lower light. Be sure to check and double-check them for pests or diseases. It is easier to treat them outside.

Unless you have a large sunroom, the hardest part may be deciding which plants get those precious bright spots in front of sunny indoor windows. Don't crowd plants together good air circulation will discourage pests and diseases. Check them periodically for signs of the most common culprits whiteflies, spider mites and scale.

Be careful not to overwater; let the soil dry between waterings and stop fertilizing. Our drier indoor air is hard on most plants. Mist them regularly or set them in trays filled with gravel and water. Turn them occasionally so all parts get equal access to the sun.

Don't worry if plants still lose some of their leaves as they acclimate to their winter home.

Don't rush them outside too early in the spring foliage may be burned by their first exposure to direct sunlight. Let them adjust by setting them out on cloudy days first and gradually move them back into stronger light.

Some examples of plants that can be overwintered as houseplants in bright light include begonias, coleus, cordyline, elephant ears, mandevilla, phormium, plectranthus, and tropical hibiscus.

Kept as dormant plants

Many woody-stemmed tropicals prefer to rest with little or no light. Their signal is not cooler temperatures but the beginning of a dry season. Prepare these plants for their move inside by reducing supplemental watering.

Move them into a crawl space, basement, or anywhere the temperature stays below 50 degrees with little or no light. Plants will eventually drop most of their leaves. Wait until spring to do any pruning, and give plants just enough water to keep them from drying completely about once a month will probably be adequate.

Awaken them in spring by repotting them in fresh soil, watering them thoroughly and feeding them with a diluted dose of liquid fertilizer. Put them in a sunny window for a month so they can adjust to higher light before moving them back outside.

Plants that can be overwintered in a cool, dark place include jasmine, brugmansia, and tibouchina.

Bulbs, corms & tubers

Plants that grow from bulbs, corms or tubers like caladium, cannas, dahlias, elephant ears and sweet potato vine receive nature's message it's time to rest when they are nipped by frost. Trim off the frost-damaged foliage and dig up the bulbs being careful not to damage them. Shake off excess soil and let them dry.

Some references suggest you wrap them in slightly moistened newspaper or peat moss. I just set them in cardboard boxes. Don't forget to label them in spring, you'll never remember what's what. Store bulbs in a cool, dark place. Check on them a few times throughout the winter and discard any that have shriveled or look rotten or moldy.

The corms of some plants like gladiolus, calla lilies and crocosmia require an additional three weeks of very warm temperatures to cure before they should be stored.

Repot the bulbs in spring. When you see new growth, begin fertilizing and move them into a sunny window.

Geraniums

If you want to save your geraniums, there are three ways: save them in pots; make them go dormant; or take cuttings.

Dig up geraniums, repot them, cut them back by a third, and put them in a sunny window. The plants may lose a few leaves and get leggy but when you prune them in spring, they will quickly rebound.

You can also force geraniums into dormancy. Dig up plants and gently remove most of the soil from the roots. Hang them upside down in a cool, dark place. Once a month, soak the roots in water and then rehang them. They will lose their leaves but when you prune and replant them in spring, they will burst with new growth.

Another way to save geraniums is to take cuttings. Cut 3 to 4 inch pieces from soft, green stems. Remove leaves from the bottom half of the cutting. Dip the stem into rooting hormone and stick it into a pot filled with vermiculite. Wrap the pot with a plastic bag to create a humid environment. After the cuttings root in 6 to 8 weeks, repot them into soil and move them to a cool, sunny spot.

Summer may just be a memory, but we can save some of our favorite plants to enjoy again next year.

•Diana Stoll is a horticulturist and the retail manager of The Planter's Palette, 28W571 Roosevelt Road, Winfield, IL 60190. Call (630) 293-1040 or visit their website at planterspalette.com.