How to Get Rid of Spider Mites on Houseplants

The Short Answer

To get rid of spider mites on a houseplant, move the plant away from the others, wash the leaves top and bottom with a forceful spray of water, then spray insecticidal soap or horticultural oil so that it wets the undersides. Repeat the spray once a week for several weeks. One treatment is not enough, because soaps and oils kill only the mites they touch and, according to University of Wisconsin Extension, mites can mature into adults in as few as 5 days in hot, dry conditions.

The sections below cover how to confirm that mites are the cause, why dry indoor air makes them worse, the routine in detail, and when a plant is not worth saving.

How to Identify Spider Mites

Spider mites are too small to see clearly without help. Wisconsin gives the size of a mature twospotted spider mite as about 1/50 inch. The UC Statewide IPM Program puts adult females, the largest form, at less than 1/20 inch, and the Royal Horticultural Society describes them as just visible to the naked eye. They are relatives of spiders, and UC notes that the adults have eight legs. Color varies from light yellow or green to dark green or brown, sometimes bright red, with two dark spots on the body. The RHS notes that they turn orange-red in autumn and winter.

Most people notice the damage before the mites. Clemson’s Home and Garden Information Center describes light-colored speckling on the upper surface of leaves and an overall faded look to the plant. UC describes the progression: a stippling of light dots at first, sometimes a bronze color, then leaves that turn yellowish or reddish and drop. Wisconsin notes that the mites also spin fine silken webs to crawl over. Yellowing alone has many other causes, which are sorted out in our guide to houseplant leaves turning yellow.

Two checks confirm it:

1. Tap a leaf over a sheet of white paper and watch for specks that start to move. UC notes that once disturbed, the mites move around rapidly.
2. Look at the underside of a leaf with a 10x hand lens, which the RHS recommends for seeing the mites themselves.

Indoors, Clemson notes that mites are more of a problem on houseplants that stay inside all year, especially palms and English ivy. Check those first.

Why Warm, Dry Rooms Make Mites Worse

Temperature sets the pace. The RHS reports that at 10°C, which is 50°F, the life cycle takes about 55 days, while at 21°C, about 70°F, development is completed in 12 days. Wisconsin adds both ends of the range: development stops below about 55°F, and in hot, dry weather mites can reach adulthood in as few as 5 days. UC’s summary is that under favorable conditions a generation can be completed in less than a week.

Each generation is also large. Wisconsin reports that a female lays up to 20 eggs per day and up to 120 in total. Colorado State University Extension gives a similar picture, about a dozen eggs daily for a couple of weeks.

Dry air helps the mites directly. Colorado State explains that they feed more under dry conditions, because low humidity lets them evaporate the excess water they take in. A heated room in winter is close to ideal for them: around 70°F and dry. UC adds that plants under water stress are highly susceptible, so a plant that is allowed to dry out too far between waterings is at more risk.

How to Get Rid of Spider Mites: The Routine

Start by separating the infested plant from the others so the leaves no longer touch, then work through the following.

Wash the plant. Clemson’s instruction is to spray sturdy plants forcefully with water, including the undersides of the leaves, to dislodge mites and break up their webs. A sink sprayer or shower does the job. Colorado State notes that a forceful jet of water physically removes and kills many mites. Clemson’s wording limits the forceful spray to sturdy plants, so go gently on delicate foliage.

Spray a contact product. Clemson says houseplants can be sprayed with insecticidal soap, and for houseplants that are outdoors it lists insecticidal soap, neem oil extract or an insecticide containing sulfur. Wisconsin calls insecticidal soaps very effective and the first choice for most spider mite problems, and notes that horticultural oil may also work with frequent applications. Colorado State is cooler on soap, rating it marginally effective against twospotted spider mite, and rates oils at the 2 percent summer rate as perhaps the most effective miticide available for home use. Our guides to reading an insecticidal soap label and to neem oil versus horticultural oil cover how the products differ. Whatever you choose, UC’s point is the one that matters in practice: oils and soaps must contact the mites to kill them, so coverage of the leaf undersides is essential.

Mind the limits. UC warns against using soaps or oils on water-stressed plants or when temperatures exceed 90°F, so water a dry plant before treating it. Clemson advises testing any spray on a small part of the plant before treating all of it, and notes that spraying houseplants is most safely done outdoors, in the shade, in mild temperatures.

Repeat weekly. Clemson notes that it is often necessary to spray once a week for several weeks. At 70°F a generation is complete in about 12 days, so mites that escaped one spray are laying eggs before a much longer gap is over. Keep going until new growth stays free of speckling and the white paper test comes up empty.

Cut off the worst leaves. Colorado State notes that webbing can keep a spray from penetrating. Removing the most heavily webbed leaves takes a share of the mites with them and makes the remaining foliage easier to wet.

What Makes Spider Mites Worse

Some general-purpose insecticides backfire. Colorado State notes that carbaryl devastates most natural enemies of spider mites and can greatly contribute to outbreaks. UC adds that carbaryl, some organophosphates and some pyrethroids also appear to favor mites by increasing the level of nitrogen in leaves. If a houseplant spends the summer outdoors, where predators help keep mites in check, avoid those products on it.

Low humidity is the other factor. The RHS states that severe damage develops quickly in warm, dry conditions, and that spraying plants with water and maintaining a high humidity reduce the risk but will not control the mite alone. A humidifier near tropical houseplants in the heating season is a reasonable supporting step.

For a greenhouse, sunroom or large collection, predatory mites are an option. The RHS names Phytoseiulus persimilis as the predator most commonly used against spider mites under glass.

Check the Neighbors and Quarantine New Plants

Mites on one plant may already have reached the plants around it. Do the white paper test on everything that stood near the infested plant, and wash and spray any that turn up moving specks. Keep the treated plant apart until several weekly checks in a row come back clean.

New plants are a common way mites arrive. Clemson recommends isolating new plants from those already in the home for six weeks, so that any pest brought in is less likely to spread. Six weeks covers several mite generations at 70°F, where one takes about 12 days, which is long enough for a hidden population to become visible.

When to Give Up on a Plant

A plant that is heavily webbed, mostly bronzed and still dropping leaves after several weeks of weekly sprays is costing more than it returns. With females laying up to 120 eggs each, it will keep seeding mites onto everything nearby for as long as it stays in the room. Bag it before carrying it out so mites are not shaken onto other plants on the way.

For a plant you want to keep despite the damage, cut away the worst growth, wash what remains, and restart the weekly routine while it regrows in isolation.