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John Fulton

John Fulton
Former County Extension Director

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In The Backyard

Horticulture columns and tips done on a timely basis

Basic Winter Houseplant Care - from David Robson

Posted by John Fulton -

Houseplants do not thrive during the winter months, states David Robson, University of Illinois Extension horticulture educator, Springfield Center. Yet, most homeowners try to "push" their plants to grow.

Tropical plants, like trees and shrubs, go through a dormant period. Leaves are not lost, but growth slows. New leaves and shoots are not produced. This natural resting state is important for a plant to build up food reserves and compensate for unfavorable environmental conditions.

Homeowners need to realize most plants grow in locations with at least 14 hours of sunlight per day, temperatures between 65 and 85 F and relative humidity approaching 100 percent. Indoor winter conditions usually only provide 8 hours of sunlight, temperatures ranging between 55 and 75 F and a humidity level of 15 to 20 percent.

When conditions are not ideal, plants enter their dormant state. That does not mean plants stop growing, Robson adds. Even leafless trees and shrubs outdoor are growing during the winter. Roots continue to absorb water, and nutrients, twigs and buds expand.

Plants easily adapt to cooler temperatures by slowing down the amount of water roots absorb and limiting new growth.

However, hot air blowing on a plant from a heat register may encourage a plant to produce weak, spindly growth. Always avoid placing plants in a direct line with hot air. Likewise, avoid drafts. Cold air can damage leaves and buds. Plants should be at least six inches from a window. Keep plants away from frequently opened outside doors.

Houseplants should not be forced into growth by using fertilizers. As a rule of thumb, avoid using fertilizers between October and April.

On the other hand, plants need as much light as possible during winter months. A typical double pane window can reduce the potential light by 80 percent. Add that to the fact that light intensity is cut by roughly 50 percent during the winter and you can see why some plants look anemic. South and west exposures provide the most light. Plants typically thriving during the spring and summer in a north or east window may need to be moved to a brighter window.

Supplement light can be added by placing the plant under a lamp. The top leaves of a houseplant should be between 10 and 24 inches under a fluorescent light and 15 and 30 inches for a typical incandescent bulb. Otherwise, you might burn the leaves. Further spacing results in less light reaching the leaves.

Water only when the plant needs it. Overwatering during the winter kills most plants. Allow all but the most sensitive plants to wilt slightly before watering. Plants can appear wilted for several days before passing the point of no return.

It is usually impossible to establish a schedule for watering during the winter. Outside and indoor temperatures have an effect. Check plants daily or weekly for watering needs.

Increasing the humidity level is the most helpful. Group plants together or purchase a cold-water humidifier or vaporizer. Plants can also be set on trays filled with pebbles and water. The pebbles prevent the plants from sitting directly in water. As the water evaporates, it creates a "mini" greenhouse around the plants. Misting increases the humidity around a plant for roughly five seconds. It might make you feel better, but it does little for the plant.

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