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posted: 10/26/2013 6:00 AM

Store terra-cotta out of elements for winter

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  • Perennials provide winter interest.

    Perennials provide winter interest.

By Tim Johnson
Chicago Botanic Garden

Terra-cotta containers are best stored out of the elements for winter. The porous clay of these containers absorbs water and the freeze-and-thaw cycles of winter can crack them if they are left outside. When the plants are finished for the year, dump out the growing medium and store the pots in a garage or shed where they are out of the rain. If you need to leave them outside over the winter, it is a good idea to store them upside down and elevated so water drains away.

Any soilless potting mix from containers can be discarded, mixed in a compost pile or blended into a garden bed. Potting mix also can be reused for one more year, as long as there has been no sign of disease in the plants that grew in it. In spring, combine the old mix with fresh soilless mix in equal parts.

In general, it is not necessary to mulch established perennial borders. A light layer of leaves in the bed will provide sufficient winter protection. However, do mulch any new perennials planted this year and especially those installed in late summer or fall. This will insulate them against freeze-and-thaw cycles in early spring that can push newly planted perennials out of the ground.

Leave interesting stalks and foliage of perennials standing for winter interest. Cut back perennials when they start looking bad.

Continue cutting your grass throughout the fall as needed, taking care to stay off the lawn when there is heavy frost present. Cold weather will eventually stop the grass plants' growth. Make your last cut of the year at a lower height of 2 inches.

Certain bulbs, such as daffodils, hyacinths, tulips and crocuses, are excellent for forcing in pots in the greenhouse or in the home. However, the bulbs still must have a cold dormant period during which they are chilled for six to 10 weeks at 40 degrees. Plant them in soilless potting mix in the fall, water them and leave the pots in a place where they will be chilled but protected from bitter cold. You may place them in a cold frame outside or plunge the pots up to their rims in soil and cover them with mulch. Do not allow the pots to dry out.

When you bring them inside in late winter or early spring, gradually acclimate them to indoor conditions by keeping them at 50 to 60 degrees for a few days.

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

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