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Issue - September 5

Early September is a good time to prepare houseplants for wintering indoors

Q. I thought I would ask this early and get a head-start on my winter garden. My potted plants that did well outside last year began to die in mid-winter. What can I do to help my plants do well indoors in the winter? I do not want to lose these plants.

A. You are very wise to consider preparing your winter houseplants now. If they are growing outside, many pests may be kept in check by natural predators (beneficial insects), but when you bring the plants indoors, these beneficial insects are often not brought in with the houseplants. On the other hand, harmful insects or their eggs may be on the plants when you bring them indoors. By watching and treating the plants now, you can help eliminate the harmful insects before you bring them indoors. Do not use strong pesticides at this time because they will also impact the population of beneficial insects. Use mild insecticides such as insecticidal soap (Be sure that the product is labeled for use on the plants you are growing. Some plants may be harmed by insecticidal soap.) However, removal of insect pests by hand or by targeted application of insecticidal soap or horticultural oil using a cotton swab may be all that is needed.

Another thing to consider is the condition of the potting soil. If the plant has been in the same soil for a couple of years, salts may have accumulated from irrigation with our New Mexico water that often contain dissolved salts. These salts accumulate in the soil over time (the rate of accumulation is affected by the amount of dissolved salt in your water and by your watering techniques). Now is a good time to repot many houseplants so that they have time to reestablish good roots before they are brought indoors for the winter. Simply moving the plants into a larger pot and placing new potting soil around the roots may not help reduce the salts. If you carefully remove the old soil, you will more effectively reduce the accumulated salts.

You can gently wash the old soil away with tap water, or by soaking the rootball in a bucket of water then gently shaking or rinsing most of the old soil away. This will minimize root damage and prevent the roots from drying as you repot. Washing the old soil away also dissolves and washes away more salts from any soil that may remain around the roots. Another benefit of repotting by removing most of the old soil is that you will also remove many insects and insect eggs that may be present in the potting soil.

Use a clean, pasteurized (disease, weed, and insect free) potting soil when you repot. Choose a potting soil appropriate to the plants you are growing. Some potting soils have additional sand or small gravel to provide drainage for cacti and succulents. Other potting soils may hold more water for plants that do not tolerate drying. Choose the proper soil.

Finally choose and prepare the indoor site where you will grow the plants. Indoor plants often receive too few hours of light, so a place near a large window is good. Sheer curtains between the plants in the window will help protect the plants from drafts and diffuse the light in a beneficial manner. Clustering plants helps maintain the humidity that plants need, humidity that is so often lacking indoors in the winter. The sheer curtain, by diffusing the light, results in more sunlight reaching farther into the room and to plants shaded by other plants in the indoor plant cluster.


For information about effective watering techniques for houseplants see the October 11, 2008 edition of Yard and Garden. This article is available at http://aces.nmsu.edu/ces/yard/2008/101108.html.

For more gardening information, visit the NMSU Extension publications World Wide Web site at http://aces.nmsu.edu/pubs/_h.

Send your gardening questions to:

Yard and Garden, Attn: Dr. Curtis Smith
NMSU Agricultural Science Center
1036 Miller Rd. SW
Los Lunas, NM 87031

Curtis W. Smith, Ph.D., is an Extension Horticulture Specialist with New Mexico State University's Cooperative Extension Service. NMSU and the U.S. Department of Agriculture cooperating.