TL;DR: Spider mites are tiny sap-sucking arachnids that feed on an extremely large variety of plants.5 Catch them early by looking for fine webbing on leaf undersides, then treat with water sprays, insecticidal soap, or horticultural oil. The best defence is always preventative measures.5
What Are Spider Mites?
Spider mites are arachnids, not insects. They have eight legs as adults, just like spiders or ticks.3 About 1,200 species have been identified so far.3
They are part of the Tetranychidae family and are one of the most common outdoor pests.5 Despite their tiny size, spider mites can do a lot of damage.5
The species most often found on indoor and greenhouse-grown plants is the red spider mite (Tetranychus urticae), also known as the two-spotted mite.1 These are around 0.5mm long.1
How to Spot Spider Mites
It is nearly impossible to see spider mites with the human eye.5 This is why they are generally not identified until after damage to the plants has been done.5
Look for silky webbing on the underside of leaves — a classic warning sign.3 For most of the year, red spider mites are a pale green colour with two dark spots on their back.1 In autumn and winter they turn orange-red.1
Spider mites feed on an extremely large variety of plants, so no part of your garden is truly off-limits to them.5
Why Act Quickly
Spider mites suck sap from plants, reducing their vigour.1 Left unchecked, they can multiply quickly and wreak havoc in a greenhouse or on house plants indoors.1
Step 1 — Isolate Affected Plants
Move any plant you suspect is infested away from healthy neighbours. Spider mites spread rapidly between plants kept close together. Keep the affected plant separate to slow the spread to healthy neighbours.
Step 2 — Use Water to Dislodge Mites
A sink or shower can be an effective first step.6 Wrap the soil and pot to protect the roots from waterlogging, then rinse the foliage thoroughly.6 This physically removes mites and their eggs from the leaf surface.
Mites reproduce quickly, so a single wash is rarely enough on its own.
Step 3 — Apply Insecticidal Soap
Insecticidal soap is one of the most widely used treatments to kill mites.6 It works by direct contact.6 Always read the product label before use.
Apply to both sides of leaves, especially the undersides where mites cluster. Repeat applications are usually needed — check the label for the recommended interval.
Step 4 — Try Horticultural Oil
Horticultural oil is another proven option to kill mites.6 It suffocates the pests and their eggs on contact. As with all treatments, follow the product label for guidance.
Avoid applying horticultural oil in very hot or very sunny conditions, as this can scorch foliage. Early morning or evening application is generally safer.
Organic Methods and Prevention
The best defence against spider mites is always preventative measures.5 Healthy, well-watered plants are less vulnerable than stressed ones.
Keep a close eye on the undersides of leaves, especially during warm, dry spells — conditions spider mites love. Early detection gives you far more options and requires far less effort than tackling a full infestation.
If you grow plants in a greenhouse, good ventilation and regular inspection go a long way. Spider mites thrive in hot, dry, and crowded conditions, so managing the growing environment is as important as any direct treatment.
Sources
- BBC Gardeners' World Magazine — gardenersworld.com
- The Old Farmer's Almanac — almanac.com
- Trifecta Natural Solutions — trifectanatural.com
- YouTube — Easy Ways To Get Rid Of Spider Mites Fast
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