Here's how to get a container garden that will survive until spring

Chicago Tribune (MCT) - It's finally spring! Our fancy turns to planting. We want to fill our lives with leaf and bloom, even if our only space is pots. The last thing we want to think about is winter.

But for container gardeners, now is exactly the time to think about protecting our plants next winter. "Anything in a container is compromised," says Brian Shea of Voltaire's Gardener in Chicago (voltairesgardener.com). "It's under extreme conditions." Plants in pots "are much more likely to dry out," he says. "They are much more exposed to the elements, including wind."

Still, those who, like Shea, design gardens on rooftops and balconies have some inside secrets to help you have a garden _ even a perennial garden, even a shrub garden _ that has a good chance to survive for years to come.

Sure, it means investing some thought, effort and even money now, before you plant. But if those preparations help you pilot plants through the rough seas of January, February and March, you can save labor and dollars in the long run over just refilling your pots each year with devil-may-care annuals.

The easiest way to overwinter perennials and small shrubs in pots is to bring them indoors _ not into the warm house, which would keep them from going through their necessary dormant period, but into an unheated place out of the wind, such as a garage or crawl space. Can't do that? Concentrate on insulating and sheltering the pots outdoors.

Though some plants might survive in some mild years without the extra effort, Chicago's crazy weather means the odds are best if we prepare for the worst. The enemy isn't just cold. It's our unpredictable swings from cold to warm and back, which can trick plants _ especially plants with their root zones exposed in pots _ into coming out of their safe state of dormancy before it's really time.

There are no guarantees. But with some help from you to snuggle in, well-chosen plants may survive to welcome future springs.

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THE RIGHT PLANT

No plant will live forever, even in an insulated pot. But here are some that have a good chance of survival for several years.

Cold-weather grasses, such as Calamagrostis x acutiflora 'Karl Foerster' feather reed grass or little bluestem grass (Schizachyrium scoparium)

Staghorn sumac (Rhus typhina)

Hosta (any cultivar)

Sedum (including tall sedums such as 'Autumn Joy' or 'Madrona')

Dwarf junipers

Perennial herbs, such as oregano or thyme

Russian sage, especially compact cultivars such as Perovskia atriplicifolia 'Little Spire'

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BUILDING A PLANT PROTECTOR

Pick the right pot: Fiberglass or high-quality plastic resin is lightweight and least likely to crack. Avoid porous terra cotta, which will crack. Ceramics, even those labeled "frost-resistant," also are risky. Concrete is heavy. For shrubs, Brian Shea, of Voltaire's Gardener, builds wooden boxes he can insulate with sheet foam.

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Pot inside pot: For perennials and smaller shrubs, it's a good idea to have two pots, one inside the other, with an inch or so of space for insulation between. Disguise the gap with mulch.

Bigger is better: Soil insulates roots, so the more soil, the better. Make sure your inside pot is at least 24 inches in diameter, says Laura Maurer of Laura Maurer Garden Design in Chicago (lauragardens.com).

Insulation: Between inner and outer pots, use several layers of bubble wrap (wrap with smaller dots is better; overlap the seams); plastic foam peanuts (in a thick layer to minimize gaps) or plastic sheet foam (found at building-supply stores), cracked to fit a round container. Don't use: paper, fabric or fiberglass insulation, which will lose all value once they get wet, or expanding spray foam, which will push your two pots apart and make a mess.

Drainage: Water must drain out of the soil to avoid root rot and ice jams. Use a high-quality potting mix for good drainage. Make sure water drains freely all the way through both pots and the insulation between them. (Suzanne Frank of Bluestem Garden Design in Chicago suggests sticking a long screwdriver in the drainage holes and "reaming it around.") Lay nylon screen or landscape fabric inside pot bottom to keep holes from clogging with soil. Elevate pot on pot feet, bottle caps or gravel so it is not sitting on a cold surface and so water can drain.

Grouping: Move pots out of the wind if you can (one reason to use lightweight pots). Group them together so they help shelter each other.

Mulch: Cover the soil surface with a 2-inch layer of shredded hardwood or other organic mulch for insulation and to reduce evaporation. But don't wrap the crown of the plant in plastic _ that can trap moisture and cause disease. Don't use plastic foam rose cones.

Water: Water well through the fall and frequently during winter, whenever water will soak in. Plants in pots lose moisture quickly.

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