Spider mites take weeks to beat, not days. Isolate the plant. Wash every leaf. Spray with insecticidal soap or horticultural oil every 5 to 7 days for at least a month. Raise the humidity so they do not return.
Mites are the pest that follows dry furnace air. Winter is when most indoor growers meet them.
How to know it is spider mites
Spider mites are not true insects. They are tiny arachnids, related to spiders and ticks. An adult is about the size of a grain of pepper or smaller, so you will see the damage before you see the mite.
Look for these signs:
- Pale speckles on the leaves. Tiny yellow or white dots, called stippling, where the mites have sucked out the contents of the leaf cells.
- Fine webbing. Thin silk strands in leaf joints and along the undersides of leaves. This means a heavy infestation.
- Dull, bronze, or yellow leaves. The leaf loses its shine, then dries and drops.
- Moving specks. Hold a white sheet of paper under a leaf and tap the leaf. Dark specks that crawl across the paper are mites.
A hand lens or a phone camera in macro mode helps. Check the undersides of leaves first. Mites live there.
Plants that mites favor include palms, calathea, alocasia, fittonia, and English ivy. Read calathea vs maranta: how to tell them apart if you are not sure which prayer plant you own. Both suffer in dry air.
Brown crispy tips alone do not mean mites. Dry air causes that too. See why are my houseplant leaf tips turning brown to sort out the cause. Stippling and webbing point to mites.
Step 1: Isolate the plant
Move the plant to a room by itself. Mites crawl from leaf to leaf when plants touch. They also drift on air currents once webbing builds up.
Check every plant that sat within a meter (3 ft) of it. Look at the undersides of leaves. If a neighbor has speckles, treat it too.
Step 2: Wash the plant
Take the plant to the shower or sink. Use lukewarm water. Spray the tops and undersides of every leaf and every stem. The water knocks off adults, eggs, and webbing.
Cover the soil with a plastic bag if the pot is small, so the plant does not get soaked. Let the pot drain.
Then wipe each leaf with a soft damp cloth. This takes time on a large plant. It removes more mites than any spray.
Cut off leaves that are mostly yellow, webbed, or dry. Bag them and put them in the trash, not the compost.
Step 3: Spray on a schedule
Washing does not kill every egg. Eggs hatch in a few days, so one treatment is never enough. A second and third round catch the mites that hatch after the first.
Choose one of these sprays:
- Insecticidal soap. Buy a product labeled for houseplants and mix it as the label says. Soap kills mites on contact, so it must wet them. Coat the undersides of the leaves.
- Horticultural oil or neem oil. Oil smothers mites and some eggs. Follow the label rate.
Test any spray on one leaf first. Wait two days. If the leaf shows no burn or spotting, treat the whole plant. Thin-leaved plants like calathea and fittonia burn more easily than thick-leaved ones.
Spray out of direct sun, and let the plant dry in a shaded spot. Oil on a leaf in hot sun can burn it.
Repeat every 5 to 7 days. Keep going for at least four weeks. Stop when you have seen no speckles, no new webbing, and no moving specks on the paper test for two weeks.
Rubbing alcohol is a common home fix. It can burn leaves and does not reach mites hidden in webbing, so soap or oil is a better choice.
Do not spray an outdoor garden product on an indoor plant unless the label lists houseplants.
Step 4: Clean the area
Wipe the shelf, the window sill, and the saucer with soapy water. Wash the pot. Mites and eggs can sit on any surface near the plant.
Wash the curtains or blinds if the plant sat close to them and had webbing.
Step 5: Change the conditions
Spider mites do best in warm, dry air. Humidity is the most useful long-term fix.
Keep the room’s humidity above about 40% if the plants allow it. A hygrometer costs little and tells you the number. A humidifier in the plant room does more than misting, which lasts only minutes. How to increase humidity for houseplants in winter covers what works.
Also:
- Move plants away from heat vents, baseboard heaters, and wood stoves.
- Dust the leaves. Dusty leaves hold more mites. Wipe them every month or two.
- Shower susceptible plants. A monthly rinse keeps the numbers down.
- Check weekly. Turn over a few leaves on each plant while you water.
What about predatory mites?
Some growers release predatory mites, which eat spider mites. They are sold for greenhouses and indoor gardens. They need the pest to be present as food, and they need the right temperature and humidity. They suit a large collection more than one sick plant. Soap and oil work for most homes.
When to let a plant go
A plant with most of its leaves webbed and dropping may not recover. Take a cutting from a clean stem if the plant roots easily, and discard the rest. Pothos, philodendron, and tradescantia root in water. Calathea does not root from cuttings. Do not bring a heavily infested plant near healthy ones for the sake of saving it.
Treat new plants as suspects. Keep them apart for two to four weeks and check the leaf undersides. The same rule applies to plants coming back indoors in fall. See how to bring houseplants inside for winter without bugs.