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Question: I recently bought a houseplant that I thought looked OK in the store, but within two weeks it was drooping and looked sick. What tips do you have for choosing healthy houseplants?

B.E., Orange

Answer: Choosing healthy houseplants before you buy is one of the most important things you can do, says Ann King, UC Cooperative Extension environmental horticultural advisor. "If you bring an unhealthy plant home, you're likely to spread the problem to all of your other plants," she says.

What's a healthy houseplant?

There are a few guidelines to keep in mind, including checking for insects, looking for overall vigorous growth and ensuring that a plant has a healthy root system.

Keep these tips in mind:

* Inspect for insects. "There are three common insects that can cause a lot of trouble for houseplants and are very hard to eradicate," says King. "They are spider mites, mealybugs and scale."

Spider mites are a common pest that live on the undersides of leaves. These tiny spiders create a very fine webbing. Under a magnifying glass or hand lens, you can sometimes see them scurrying around. They are sap-sucking pests that cause small yellow speckling on leaves. Eventually the foliage dries up and falls off.

Mealybugs are another common sap-sucking pest. These pests, fairly easy to see, have a white, waxy, fluffy-looking coating that serves as a layer of protection. They like to hide on the root crown, the underside of leaves and the leaf axils. Root mealybugs can be found among the roots when the plant is removed from the pot. Cacti and succulents are particularly at risk for both types of mealybugs.

Scale is also common. The adults of these little insects press tightly to plant stems and the underside of leaves. They come in a variety of colors, including green, brown, orange and gray, and have a round, hard coating on the outside. They don't move much, but suck energy from the plant.

* Look for healthy, vigorous growth. You want a plant that is buoyant, with a vibrant sheen. The leaves should hold themselves up well. Saggy, drooping foliage is a sign that a plant has been "droughted" too much, or is an indication of a bacterial root problem, which means the plant can't take up water. New growth should be normal in size and not mushy. Small, soft new leaves indicate root rot.

Also stay away from a plant with an excess of dried leaves or brown leaf tips, which are a sign of water stress.

* Check plant anchoring. Stems should be solid and firmly embedded in the soil. A loose stem indicates root rot.

* Inspect for healthy roots. If it's feasible, pull the plant out of the pot and look at the roots. They should be white and firm. While some roots are naturally yellow, virtually no roots should be brown and mushy; this is a sign of disease.

* Avoid root-bound plants. Check the plant's root mass. If it is heavy and circling in the pot, the plant has probably been in the container too long and may be weakened as a result.

* Look for a plant that is well-proportioned to its container. "Don't get a plant that is way too large for a little pot, or a pot that is way too big for a plant, because both conditions will encourage root problems," says King. "The plant should look visually balanced in the container."

* Consider the sales location carefully. Does the nursery have a good turnover in plants? "If plants sit in a location for an extended period of time, insects have a chance to build up their populations and the plants become stressed," King says. "How knowledgeable are the sales staff? Are the plants located in the growing conditions they would normally require? Plants in a dark location will suffer if they stay there for any length of time."

* Listen to your instincts. Sometimes plants seem fine in the nursery, but show signs of a problem a week or two after you get them home. Even though a plant may seem to be growing well, if you feel that something is not quite right, don't take a potential problem plant home.

Have a problem in your yard? University of California Cooperative Extension Master Gardeners are here to help. These trained and certified horticultural volunteers are dedicated to extending research-based, scientifically accurate information to the public about home horticulture and pest management. They are involved with a variety of outreach programs, including the UCCE Master Garden hotline, which provides answers to specific questions. You can reach the hotline at (714) 708-1646 or Calls and e-mail are picked up daily and are usually returned within three days.

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