Black dots on house plants' leaves

I have little black dots on the underside of some of my house plants, including the stalks. What could this be and how do I treat it? -Kelly

Are the dots moving? Are they easily smashed? Do they rub off easily? Is there a sticky substance around the drops or on the leaves and stems below? You may be observing insects on your house plants. If they rub off easily and are easily smashed, they may be aphids. These may be washed off the plant by placing them in the sink or bath tub and washing the plants with a strong stream of water. You will need to repeat the process periodically. You can also use insecticidal soap (a safe insecticide for indoor use). Put the plants in the sink or place an old sheet or a plastic sheet under and behind the plant so that the spray will not damage carpet, upholstery, or draperies. If you wish to use other, stronger insecticides, wait for a period of warm days when you can apply the insecticide outside and leave the plants there until the product has dried and there are no objectionable odors. If the spots don't rub off or smash, you may have scale insects which are more difficult to treat. However, these may be treated with horticultural oil (more likely to stain fabrics in the house than the insecticidal soaps). Before treating the plants, be certain that the spots are not natural pigmentation. Some plants will produce such spots naturally. When using chemicals for pest management, be sure to read, understand, and follow the directions on the pesticide container.

Winter protection for tender plants

We corresponded a little last summer regarding the tropical plants in my townhouse courtyard in Phoenix, AZ. You may recall that I was having problems with the leaves burning because the Saltillo tile drew heat into the courtyard and there was little or no shade. I took your advice and they survived. Now my problem is the cold. Because the plants are surrounded on all sides by either block walls or wood and because they sit on the tile, the area is very cold. We will have some temperatures below freezing this winter, and I don't know what to do to keep them safe.

The safest course of action is to bring the plants indoors when freezing weather is likely. If this lasts for only a few days, the plants will not be harmed if they are kept in a dark room. If a prolonged stay indoors is necessary, place them in a brightly lit room, preferably near east- or south-facing windows. It is okay to return the plants outside when the days are warm, but bring them indoors if the nights will freeze. To make it easier to move the plants, larger potted plants may be placed on platforms with casters allowing them to be rolled in and out. This may also work for collections of smaller potted plants, reducing the number of in and out trips to move your plants. Remember to water the plants as they dry more quickly in the drier indoor environment.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!