How to Kill Spider Mites on Houseplants

The first signs of spider mites on houseplants are the symptoms they cause, such as yellow speckling on leaves -- the mites themselves are tiny and difficult to see. Relatives of insects, spider mites are divided into different species, which infest different plant types. The most common cause of houseplant infestations is the twospotted spider mite (Tetranychus urticae). As well as yellow speckling, spider mite infestation symptoms include a gray or bronze tint to leaves and fine webbing.

Regularly rinsing houseplants or spraying them with horticultural oil or soap sprays controls spider mites, but the best method for long-term control is growing healthy houseplants and providing humid conditions.

Rinsing Plants

Regularly rinsing houseplants infested with spider mites helps control light or moderate infestations.

Spraying Infestations

Horticultural soaps or oils control heavy infestations of spider mites on houseplants, and the soaps and oils aren't harmful to humans. Houseplants that are heavily infested with spider mites are severely discolored, and they wilt and drop their leaves. Apply a ready-to-use horticultural soap once per week or every three or four days, as necessary. Spray the horticultural soap over all the houseplant parts, including the undersides of leaves, until the entire plant is saturated.

If a houseplant is severely infested and not valuable, consider simply discarding it to reduce the risk to other plants.

Caring for Houseplants

Well-watered and fertilized houseplants placed on trays of pebbles and water are unlikely to suffer badly from spider mite infestations.

Most houseplants need water when the potting soil surface is dry. Pour water over the potting soil surface until it flows through the container drainage holes, and allow the plants to drain before replacing them on their drip trays.

Many houseplants benefit from fertilization with a 12-4-8 fertilizer every one to two weeks. Dilute the fertilizer at a rate of 1 teaspoon per 1 gallon of water, and pour it over the potting soil surface. You can apply fertilizer instead of water if the plant needs water.

Stand houseplants in their drip trays on shallow trays filled with pebbles and water, which humidifies the air around the plants. Alternatively, mist the houseplants every day with clean, cool water in a hand mister.

Preventing Infestations

Spider mite infestations on houseplants often spread through new plants and plants moved indoors from outside. Spider mites spread by walking over leaves onto new plants, or drifting on strands of webbing that float currents of air. Keep new plants in a different room, away from other houseplants for one month, and check the leaves regularly for signs of spider mites.

Houseplant Pests: Spider Mites

Spider mites are so small that they are usually hard to see with the naked eye. Adult Pacific spider mites stand out because they have a bright red first pair of legs. You'll often see spider mite damage before you notice the little critters themselves. The affected foliage occasionally takes on a bronze cast. Severe spider mite damage weakens and often kills houseplants. In dry, dusty conditions, a spider mite can complete its entire life cycle in less than a week, which is incredibly fast. Spider mites live in colonies, usually on the undersides of leaves. Make sure that spider mites are actually living on your houseplant before treating it. Your best bet, then, is using cultural controls. Since spider mites prefer houseplants with dusty leaves that are suffering from water stress, you must make sure that you properly irrigate your plants and wipe off dirty leaves with a wet rag. Trim off any heavily infested leaves and discard them immediately.