Monitor houseplants for insect problems that often occur when plants become stressed due to insufficient light, overheated rooms, or improper watering and fertilizing techniques. New houseplants or gift plants can also harbor pests. Isolate these plants before adding them to your collection. Pests to look out for include the following:

• Spider mites — Look for webbing in leaf axils, stippled foliage and weak, off-color leaves. Mites are often difficult to see without a lens.
• Scale — Characteristic sticky, clear honeydew is produced on leaves by these small, immobile, rounded insects usually found on stems and veins of leaves.
• Mealybugs — Easy to spot, these insects resemble crowds of tiny cotton puffs.
• Whitefly — Whiteflies are a major problem in many greenhouses because they can quickly move to neighboring plants. Look for tiny, white, mothlike insects often found on the undersides of leaves.
• Fungus gnats — The adult black gnats fly around the plant but do no damage. The immature larvae in the moist soil can chew plant roots. They are often a problem in overwatered plants or overly moist flats of seedlings.