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.
Regularly rinsing houseplants infested with spider mites helps control light or moderate infestations.
Wrap plastic bags around the houseplant containers and over the potting soil surface.
Loosely tie the bags around the houseplants stems with twine or elastic bands.
Rinse the houseplant leaves and stems with lukewarm water in a shower. Closely rinse the lower leaves and the undersides of the leaves.
Rinse the houseplants in the same way at least once every week.
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.
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.