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Issue: February 12

Mid-winter houseplant problems may be insects, mineral salt accumulation, or other things

Q. My houseplants were looking pretty good until about 2 weeks ago. I brought them indoors from their summer home in October and they have been wonderful. Now, however, the leaves are turning yellow, brown, or otherwise not looking healthy and falling from the plants. What is wrong? What can I do?

A. What you are describing is not unusual. Plants that were outdoors during the summer and growing well are able to come indoors and do well until mid-winter. Then any one or more of several problems often beset them. The most common problem to develop in mid-winter is the buildup of insects. When you first brought the plants indoors, insect pests had been kept to a minimum by predatory insects outside. Once you brought them indoors, you removed them from the source of "good insects" that kept the population of "bad insects" at low levels. After a few weeks to a couple of months, the population of spider mites (not actually insects, but like damaging insects), or the population of aphid, scale, mealy bugs, and other plant feeding insects began to increase. Healthy plants are able to continue to look good until these populations reach high enough levels to damage the plants. Look for signs of these pests (the pest, their shed skins, etc.) or the symptoms (stippling and discoloration of the leaves). If you observe these symptoms, you can treat them to a shower of luke warm water in the bathtub, or a spray with insecticidal soap (also in the bathtub or with plastic sheets to protect carpets, draperies, and upholstery). You may need to treat several times to reduce the pest population. Continue watching for signs and symptoms and retreat as needed until the plants can be safely moved outdoors again. Another common problem is the accumulation of mineral salts in the potting soil. New Mexico waters contain dissolved minerals that remain in the soil after the plants use the water or the water evaporates from the soil. As these minerals build up they can cause burning of the leaves called "salt burn". Proper irrigation practices can help slow the accumulation of these salts, and repotting with fresh potting soil can give the plants a new start. Diseases are unlikely, but not completely impossible problems. If you think a disease (or insects) has caused the problems, take a sample to your local NMSU Cooperative County Extension office. The professionals there can help you identify the problem and best solution. Cold drafts or hot dry air from forced air heating systems can also cause damage to leaves and drying of leaves. To help minimize this, keep the plants away from drafts on the coldest nights and away from the blast of warm dry air from the furnace. Place pots on trays of moist pebbles to add humidity and cluster plants near each other so water lost by the plants collectively humidify the air near the plants. When the weather permits, repot and move the plants outdoors so they can renew their strength for the challenges of indoor live next winter.


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.