How to get rid of spider mites

Spider mites breed fastest in warm, dry air, on plants that are short of water and on dusty leaves. Indoors that usually means a plant standing above a radiator in the heating season.

The University of Minnesota Extension names spider mites as the number one houseplant pest and notes that they thrive in warm, dry conditions, which is what a heated home offers in winter. Its advice is to check plants regularly by tapping leaves over white paper and looking for orange specks, and to wash houseplants regularly through the winter months.

They arrive on new plants, on cut flowers and, outdoors in summer, on the wind. Once one plant has them, they walk across touching leaves and drift on their threads to the next. Adult females can rest in cracks around the pot rim, the windowsill and in plant debris, which is how a cleaned plant gets them back.

The plants that get them most are thin-leaved and humidity-loving ones: calathea and maranta, alocasia, palms, ivy, croton, schefflera, ficus, dracaena, yucca and citrus. Succulents such as jade get them in dry winter rooms too.

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   Step 1. Separate the plant. Carry it out of the group the moment you find mites.

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   Step 2. Rinse it thoroughly. Shower it with lukewarm water, aimed up at the leaf undersides, the leaf joints and the shoot tips. Tilt the pot or bag the soil. A forceful rinse knocks off a large share of the mites and breaks up the webbing. Repeat every few days while you treat.

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   Step 3. Cut off the worst leaves. Leaves that are gray and covered in webbing do not recover and carry most of the colony. Bag them and put them in the bin. Wipe the windowsill, the cachepot and the saucer.

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   Step 4. Use labeled insecticidal soap. It kills mites it directly wets, so cover the leaf undersides, joints and stalks as instructed. Many treatments miss eggs. Follow the label for repeat applications rather than a fixed ten-day schedule, and test a small area for leaf damage first.

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   Step 5. Or a horticultural oil. Plant or mineral oils sold for houseplants smother mites under a film and need the same full coverage. They can damage hairy leaves and young growth and strip the natural powdery bloom from succulents, so the leaf test applies. Never use soaps or oils in full sun, above about 32 °C (90 °F) or on a plant that is short of water.

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   Step 6. Release predatory mites. Phytoseiulus persimilis is the standard biological control: it eats all stages of spider mites and works best in a heavy infestation, at room temperature and above about 60 % humidity. Neoseiulus (Amblyseius) californicus copes better with lower mite numbers and drier, cooler conditions and suits prevention. As a guide, release about one predator for every ten spider mites, stop spraying a week before, and give them several weeks. They work better among grouped plants than on one pot in dry room air.

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   Step 7. A miticide for houseplants. If rounds of soap or oil fail, use a miticide whose label names houseplants and spider mites, exactly as the label says. Ordinary insecticides are the wrong choice: several kill the mites' natural enemies and can make an outbreak worse.

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   Step 8. Keep checking. Inspect undersides, joints, shoot tips and leaf stalks every two to three days. Rinse or wipe away mites you find. Repeat a pesticide only at its labeled interval. Return the plant after two clear checks in a row and keep checking its neighbours for weeks.

Lukewarm water is the most effective home remedy you have. A strong rinse of the undersides, repeated every few days, keeps numbers down.

Dish soap such as Dawn is a detergent, not an insecticidal soap. It can kill mites it wets, but its additives can spot and scorch leaves. Use a soap sold for plants instead.

Isopropyl alcohol of 70% or weaker kills the mites it wets and can also damage leaves. Dab it on one leaf first and look at that leaf again after one to two days before you use it anywhere else. Never use denatured spirit. For a whole plant, rinsing and insecticidal soap do the same job more gently.

Neem oil works like other oils, by smothering. It needs full coverage and repeat rounds and can mark sensitive leaves.

Higher humidity slows mites but does not end an infestation. Use it as prevention.

A clear plastic bag over the plant for a few days raises humidity sharply and is a popular tip. It slows the mites, but still damp air invites rot and leaf damage, and we found no independent trial showing it ends an infestation. If you try it, keep it short and air the plant daily.

Hydrogen peroxide, vinegar and baking soda have no good evidence against spider mites and can burn leaves.

At 21 °C (70 °F) a spider mite develops from egg to adult in about 12 days. At 10 °C (50 °F) it takes about 55. In a warm, dry room a generation can be done in under a week, so numbers climb fast.

Control often takes several weeks. Inspect every two to three days, remove mites you find and repeat any pesticide only at its labeled interval. Predatory mites also need time and the supplier’s conditions. Look for new growth without fresh speckling.

Not to people or pets. Spider mites feed only on plant sap. They do not bite or live on people, cats or dogs.

To plants, yes. A light infestation weakens a plant. A heavy one strips leaves of their green, dries them out and makes them drop, and a badly damaged plant can die. That is why speed matters more with spider mites than with most houseplant pests.

Whether a plant itself is a problem around pets is covered in its own care guide.

Move sensitive plants away from radiators in winter and group them, or stand them on a pebble tray. Humidity does not cure, but it slows mites.

Water by feel. Mites favour plants short of water.

Wipe or rinse large leaves regularly. Dust hides early speckling and favours mites.

Keep every new plant apart for two to four weeks and check the undersides in that time.

Look at the undersides of your mite-prone plants once a week in the heating season.

Give up on a plant that is mostly gray and webbed, keeps reinfesting your other plants after several rounds of treatment, and is easy to replace. Extension services advise that discarding a heavily infested plant is often better than treating it for months. Bag it before you carry it through the house.

A valuable or large plant is worth the weeks: cut it back hard to the healthy parts, rinse, treat in rounds and release predatory mites.

Speckled, silvery gray leaves do not turn green again. They stay that way until they drop, and you cut them off only if the plant keeps enough healthy foliage.

New growth tells you whether you are through. If it comes in evenly green and without dots, the treatment worked.

A badly weakened plant needs time rather than fertilizer. Give it a bright spot, water by the finger test and wait with feeding until it grows again.

Whether a plant is a problem around pets or children is covered in its own care guide. If you suspect poisoning, a vet or a doctor is the right call.

New plants, gift plants and cut flowers are how spider mites usually get into a home, and a plant in flower or still in its sleeve is easy to wave through. Check it on the day it arrives, before it stands with your other plants.

Take off the sleeve or wrapping and put it in the bin. At a bright window, turn five or six leaves over and look along the main vein on the underside, then at the leaf joints and the shoot tips. Pale speckles on the upper side are the reason to look closer.

Tap two or three shoots over a sheet of white paper and wait a few seconds. Specks that start to walk are mites. In autumn and winter they are often orange or red.

For a close look, use a hand lens or your phone camera at full zoom. Mites have eight legs and an oval body, the eggs are tiny clear spheres, and white cast skins sit beside them under the leaf. Webbing in the leaf joints means the colony is already large.

Then keep the plant in another room, or at least where its leaves touch no other plant, for two to four weeks and check it every two to three days. A clean first check does not rule out eggs.

Write the next check down the moment you find mites or bring a plant home. During treatment it is due two to three days after each rinse. Rinse on a Saturday, look again on Monday or Tuesday, at the same leaf undersides, joints and shoot tips.

After two clean checks in a row, the plant can go back to its spot. From then on, look at the undersides of your mite-prone plants once a week until the heating goes off in spring. New growth without fresh speckles tells you the plant is through.

For a new or gifted plant, check on the day it arrives, again three or four days later and then weekly until its two to four weeks apart are over.

If you use Botanicaly, “Ask about this plant” (Pro) lets you photograph the leaf and ask about it. Botanicaly reads the photo together with the care details you saved for that plant, suggests possible causes and what to try first, and tells you when to check again. A photo cannot confirm mites the way the paper test can, and no app can promise that a treatment works, so the checks on this page still decide. Everything on this page works without the app.