Spider mites are tiny pests that suck the sap out of leaves. They are not insects. They are arachnids, related to spiders and ticks, and they have eight legs. The most common one in homes and gardens is the two-spotted spider mite (Tetranychus urticae).
Spider mites are so small that most people see the damage before they see the mites. They breed fast in hot, dry air. That is why they show up on houseplants in winter and on garden plants in hot summers.
Signs of spider mites
- Tiny pale or yellow speckles on the leaves, called stippling
- Leaves that look dull, dusty, or bronze
- Fine, silky webbing under leaves and where leaves meet stems
- Leaves that turn yellow, dry out, and drop
- Tiny moving dots, often near the webbing
The white paper test
Hold a sheet of white paper under a leaf. Tap the leaf a few times. Wait a moment and watch. If tiny specks start to crawl across the paper, you have mites. Smear one with your finger, and it leaves a streak.
Why you have spider mites
Spider mites thrive in hot, dry conditions. Indoors, dry furnace air in winter is the usual trigger. Outdoors, they flare up in hot, dry summers, on dusty plants near roads, and on plants short of water.
In warm conditions, a new generation can go from egg to adult in about a week. A few mites can turn into thousands in a few weeks.
Broad-spectrum insecticides can make mite problems worse. Many do not kill mites, but they do kill the predators that keep mites in check.
How to get rid of spider mites
Step 1: Isolate the plant
Move an infested houseplant away from your other plants. Mites crawl and drift from plant to plant. Check the plants that sat next to it.
Step 2: Rinse them off
Take the plant to the shower or sink. Spray the leaves hard with lukewarm water, tops and undersides. This knocks off many of the mites and breaks up their webs. For big, smooth leaves, wipe each one with a damp cloth.
Outdoors, use a strong spray from the hose in the morning. Repeat every few days.
Step 3: Spray with insecticidal soap or oil
Insecticidal soap and horticultural oil, including neem oil, kill the mites they touch. The spray has to coat the mites, so soak the undersides of every leaf until it drips.
- Test the spray on a few leaves first and wait a day.
- Do not spray in direct sun or when it is above 90°F (32°C). Leaves can burn.
- Do not spray a dry, wilted plant. Water it first and spray the next day.
Step 4: Repeat every 5 to 7 days
Sprays do not kill the eggs. Treat every 5 to 7 days for at least 3 weeks to catch each new hatch.
Step 5: Raise the humidity
Spider mites do best in dry air. Group houseplants together, run a humidifier, or set pots on trays of wet pebbles. A quick mist from a spray bottle does little on its own.
Predatory mites
Predatory mites eat spider mites and their eggs. They work well in greenhouses, sunrooms, and gardens.
- Phytoseiulus persimilis feeds on two-spotted spider mites. It works best in warm, humid conditions.
- Neoseiulus californicus handles hotter, drier conditions. It can live on pollen and other small prey when spider mites are scarce.
Release them early, before the plant is covered in webbing. Do not spray soap or oil after you release them, or you will kill the predators too.
When to throw a plant out
A small houseplant covered in webbing, with most of its leaves yellow, is hard to save. Bag it and throw it out. That protects the rest of your plants.
Plants spider mites love
Indoors, spider mites go after palms, ivy, crotons, scheffleras, and poinsettias. They can also hit orchids in dry rooms.
Outdoors, watch beans, cucumbers, tomatoes, eggplant, strawberries, and roses. These posts help you grow them well:
How to prevent spider mites
- Check new plants before you bring them home. Look under the leaves.
- Keep new houseplants apart from your others for a couple of weeks.
- Rinse or wipe houseplant leaves every month or two.
- Water garden plants during dry spells. Stressed plants get mites first.
- Hose the dust off plants near roads and driveways.
Other houseplant pests
Not sure what you are looking at? These posts can help:
Indoor plant shops I recommend
Good plants and good supplies make indoor growing easier.
- The Sill: houseplants and potting mix delivered
- Click & Grow: the smart garden I use for indoor herbs, 31% off with code HHARVEST from November 3 to 30
- My Amazon storefront: the tools and supplies I keep coming back to
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