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Sally Cunningham: Keeping plants alive

Even good gardeners and horticulture professionals struggle with this question: “How can I keep this plant alive over the winter?”

The problem is not about knowing what the plants need – science is clear on temperatures, moisture, care for most plant groups. The problem is: How can we provide the right conditions in our houses, basements, garages or yards? We don’t have conservatories or greenhouses with temperature controls, so we have to work with what we have.

Our conditions aren’t perfect.

Tropical bulbs, corms, tubers

Cannas, caladiums, elephant ears and many other tropical plants can go dormant in winter and saved for future seasons, since their tubers (or bulb-like structures) store enough energy to produce growth when spring comes.

Dig them up now (OK, even after some frosts), and cut off the foliage. Lightly brush off soil and air-dry them. (Some pros suggest hanging them upside down while drying). When the skin is wrinkled, pack them in peat moss, sand or sawdust, not touching each other. (Some gardeners dust them with a fungicide.)

Store them in a crate, chest or bag in a place that stays about 40 to 45 degrees ...

And there’s the problem: Many basements are too warm, and detached garages are too cold. Find the right spot, and check occasionally for rot – remove and destroy.

If your conditions were right you’ll see new growth in late winter and proceed to repot and move into the light.

An alternative approach is keeping some bulb or tuber plants in the house as houseplants. It’s all about the indoor conditions you can provide.

Tropicals, annuals, houseplants

It can take a lifetime of study and experimentation to figure out how to keep tropical or tender plants indoors in the winter. Every plant has particular needs for light, water, humidity, nutrients, repotting and problem prevention. House conditions vary, even from room to room. Just when you have your favorites figured out, a new plant on the market will tempt you to try it.

Start with the general guidelines, and see which plants suit your household conditions.

• Easy foliage plants: Snake plants, philodendrons, Aspidistra (cast iron plant), Dieffenbachia and Setcreasea (purple heart) are among the traditional houseplants that accept quite imperfect conditions.

• Flowering houseplants: Begonias, Abutilon (flowering maple), some salvias, geraniums, Oxalis, Anthurium, Streptocarpus, Clivia and crown of thorns are just some of the houseplants or container plants that can flower. Most need brighter light than foliage plants, and some are fussy about overly warm or cold temperatures.

Hardy plants you didn’t plant

A gardener’s saying: “If you don’t have plants sitting in your driveway in September, you didn’t buy enough plants!”

So now what to do with the perennials, shrubs and small trees?

• Woody plants: Consider how these plants would be kept in a nursery: They will be outside in their containers, in a cold but sheltered area. My best choice is on the east side of a building, with mulch piled around them after their soil is frozen. An unheated building could work, but watch when they need water and moisture in spring. You can also plant them even now, with a wide hole (the top just slightly above soil level), backfilled with a compost/soil mix. Water until freezing.

• Perennials: Plants with small root balls don’t usually thrive if planted in the ground late. Freezing and thawing dries out roots easily. Group potted perennials in boxes or on shelves and keep them in an unheated garage. Or sink them into a holding trench, packed with leaves. The goal is to provide consistent frozen conditions without any extremes.

The guidelines here are basic (See additional tips below.) Keep trying. Keep learning. Most plants are worth saving.

Best indoor conditions

Try to meet these requirements to help most plants at home or in the office:

• Light: Most plants need more light than northern interiors offer. Provide as much bright, indirect light as possible, and try supplemental LED, fluorescent or grow lights.

• Water: Feel soil with your finger, or lift plants, to learn which ones dry out fastest. Most plants need water when the top of soil is dry, but a few (peace lily) need continual water, and others (cacti) infrequent watering. Overwatering kills many plants.

• Temperature: Most plants thrive around 70 degrees in the daytime, and 60 to 65 degrees at night.

• Humidity: Especially plants with tropical origins need humidity, but most houses are drier than deserts. Misting is almost inconsequential. A humidifier is valuable. Set plants on bricks or pebbles above pans or trays holding water.

• Fertilizer: To keep plants flowering, use a regular houseplant fertilizer. Most plants benefit from resting without fertilizers (and less water) through winter.

Sally Cunningham is a garden writer, lecturer and consultant.

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