Albert Bridge / Wikimedia Commons — source (CC BY-SA 2.0)
Spider mite infestation
Tetranychidae family; commonly Tetranychus urticae (two-spotted spider mite) and Oligonychus ununguis (spruce spider mite)
Spider mites are tiny arachnids that spin fine webs on leaf undersides and cause yellow stippling on plant tissue. Control early by spraying water to dislodge them, raising humidity, and introducing predatory mites if the problem persists.
Spider mites are tiny arachnids that feed on plant sap, causing stippled, yellowed leaves and fine webbing on stems and leaf undersides. They thrive in warm, dry conditions and reproduce rapidly—a single female can lay dozens of eggs that hatch within days. Infestations can spread from plant to plant in less than a week if left unchecked. They're a common problem on both houseplants and outdoor crops, particularly in sheltered or heated environments.
Outdoor spider mites peak from late spring through summer as temperatures warm; indoor and greenhouse infestations worsen in autumn and winter when heating is on and humidity drops. Cool-season species (spruce mites) are active in spring and autumn.
- •Spider mites are tiny arachnids identified by fine webbing and yellow stippling on leaves; early detection using the white-paper test is crucial.
- •They reproduce rapidly in warm, dry conditions—one generation can complete in 7–10 days, so infestations escalate quickly without intervention.
- •Start with water spray and humidity; if that fails within 2 weeks, add insecticidal soap or predatory mites (Phytoseiulus persimilis).
- •Never spray pesticides if using biological controls; predatory mites are killed by most chemicals.
- •Quarantine new plants, inspect undersides weekly, and keep foliage misted to create unfavourable conditions for mites.
- •Severe infestations may take 3–4 weeks to clear with organic methods; consistency and repeat applications are essential.
Not sure if it's spider mite infestation?
Snap a photo of your plant and GrowDo Vision will check for signs of spider mite infestation and other common problems — with tailored treatment advice for your garden. Free during your trial when you sign up.
How to identify
Spider mites are nearly invisible to the naked eye (0.5mm), but their fine, silky webbing on leaf undersides and stems is the clearest sign. Use the white-paper test: tap foliage over white paper and look for tiny moving dots. Crush them with your finger—plant-feeding mites produce a green streak, while beneficial predatory mites streak yellow or orange. Early detection before visible damage appears is crucial.
Damage and symptoms
yellowcloud from Germany / Wikimedia Commons — source (CC BY 2.0)
Infested leaves show fine yellow or pale stippling (tiny dots) where mites pierce cells to feed. Leaves may eventually turn bronze, brown, or grey and drop prematurely. Fine webbing covers leaf undersides, stems, and branch junctions. In severe cases, entire plants weaken and growth halts. Conifers lose colour and vigour; ornamentals and vegetables become unmarketable or unproductive.
Lifecycle
Albert Bridge / Wikimedia Commons — source (CC BY-SA 2.0)
Eggs hatch in 2–4 days; nymphs develop in another 2–4 days. Adults live 2–4 weeks and lay dozens of eggs daily. A complete generation takes 7–10 days in warm conditions, allowing multiple overlapping generations per season. Cool-season species (e.g. spruce mite) go dormant in summer heat; warm-season species peak in spring and autumn indoors or year-round in heated spaces.
Most affected crops
Prevention
Maintain humidity and avoid dry stress
Spider mites favour warm, dry air. Regular misting of foliage, grouping plants together, or using a humidifier creates less favourable conditions. Ensure plants are well-watered at the roots; drought-stressed plants attract and support heavier infestations. Avoid placing plants near heating vents or in full, hot sun without shelter.
Quarantine new plants
Inspect all new plants carefully before introducing them to your garden or greenhouse. Isolate them for at least two weeks and check undersides of leaves weekly. Spider mites spread easily on contaminated clothing, tools, and plant material—clean hands and equipment between handling different plants.
Scout regularly
Check plants weekly, paying close attention to leaf undersides. Early detection before visible damage prevents rapid spread. Use the white-paper test to confirm mites present before damage is obvious. Remove heavily infested leaves or plants promptly to limit population build-up.
Avoid broad-spectrum pesticides
Many insecticides kill natural predators of spider mites, allowing populations to explode. Restrict chemical use to target treatments only, and never spray if you're using biological controls such as predatory mites or lacewings.
Organic control
Strong water spray
The first line of defence. Use a forceful stream of water to physically dislodge mites and their webbing from leaf undersides. Repeat every 2–3 days for a week or two. This also raises humidity around the plant. Avoid damaging soft growth; early morning or evening application is gentler.
Insecticidal soap
Organic-approved soft soaps (potassium salts of fatty acids) coat mite bodies and disrupt their cell membranes. Spray thoroughly, covering all leaf surfaces, especially undersides. Repeat every 5–7 days as needed. Test on a small area first; some plants are sensitive. Most effective on light infestations.
Predatory mites
Release Phytoseiulus persimilis, Amblyseius species, or Metaseiulus species onto infested plants. One predatory mite per ten spider mites can reduce populations significantly. These are blind and navigate by webbing, so place them directly on affected foliage. Avoid pesticides once released; they may establish and provide ongoing control on perennials.
Neem oil or plant oils
Organic neem oil suffocates mites and eggs. Apply in early morning or evening to avoid leaf scorch in strong sun. Follow label rates and repeat every 7–10 days if needed. Less effective than water spray or predatory mites alone, but useful as part of an integrated approach.
Chemical control
Miticide sprays (acaricides)
Approved UK products containing sulphur or other acaricides (e.g. those based on clofentezine or fenazaquin where available) target spider mites specifically. Always check current UK product approval before purchase, as listings change. Apply according to label instructions and repeat if necessary. Rotate active ingredients to prevent resistance.
Companion plants and deterrents
Frequently asked
How do I know if I have spider mites and not another pest?
Spider mites are unique for their fine webbing on leaf undersides and stems—no other common garden pest produces this. Use the white-paper test: tap foliage over white paper and look for tiny dots moving slowly. Crush one with your finger; if it leaves a green streak, it's a plant-feeding mite. Stippling (tiny yellow dots) without webbing may indicate thrips or mites, but webbing is diagnostic for spider mites.
Can spider mites harm me or my family?
No. Spider mites feed only on plants and do not bite humans or pets. They are not disease vectors. The only concern is plant damage and potential crop loss. However, some people with severe allergies may react to airborne mite particles in very heavy infestations, though this is rare.
Why do spider mites keep coming back?
Spider mites reproduce extremely fast (7–10 days per generation) and lay hundreds of eggs. If you kill adults but miss eggs or if conditions remain warm and dry, survivors quickly repopulate. Incomplete coverage of leaf undersides during treatment is common. Consistency over 2–3 weeks is essential. Also check nearby plants; mites spread easily between neighbours.
Will water spray alone solve a heavy infestation?
Water spray works well for light to moderate infestations if repeated every 2–3 days for at least two weeks. For severe infestations (many leaves heavily webbed, visible damage spreading), combine water spray with insecticidal soap, neem oil, or predatory mites for faster control. Heavy infestations may take 3–4 weeks to clear with organic methods alone.
Is it safe to use predatory mites alongside other treatments?
Predatory mites are killed by most insecticides and miticides. If you release them, avoid all sprays for at least 2–3 weeks. However, water spray and humidity adjustment are safe companions. Once established on perennial plants, predatory mites may persist year-round and provide ongoing control without further intervention.
Can I grow companion plants to prevent spider mites?
No single companion plant repels spider mites reliably. However, maintaining diverse plantings with natural predators nearby (lacewings, ladybirds, thrips) helps suppress populations. Avoid monocultures and keep plants healthy and well-watered; stressed plants are more attractive to mites. Removing weeds and debris eliminates mite overwintering sites.
Are spider mites worse indoors or outdoors in the UK?
Indoors, spider mites thrive year-round in warm, dry central heating. Outdoor infestations peak in spring and autumn; summer heat (above 25°C) can slow reproduction for some species. Unheated greenhouses see problems in spring and autumn. Heated greenhouses and homes are at risk all year. Increasing humidity and reducing temperature indoors helps control them.
How quickly can spider mites spread from one plant to another?
In ideal conditions (warm, dry, close spacing), spider mites can colonise a neighbouring plant in less than a week. They crawl between touching foliage and are carried on wind, tools, and clothing. Isolation of infested plants and regular inspection of nearby plants are essential to prevent spread. Quarantine new plants for at least two weeks before placing them near established stock.
Grow with confidence
Join GrowDo to scan your plants, track your harvests, and get timely reminders before pests like this take hold.