Last updated on October 23rd, 2023 at 08:15 pm
Weakened houseplants and in addition the dry heating air in winter – ideal conditions for the common spider mite (Tetranychus urticae). The tiny mites are only about 5 mm in size, but their sucking activity on the leaves can cause great damage. Infestation is often not detected until many silvery white to yellow spots appear on the leaves, which merge into larger spots in more severe infestations. Heavily necrotic leaves fall off after some time. The initial yellowish speckles are often misinterpreted as deficiency symptoms. On closer inspection, fine webs can also be seen. When spraying the plant, these become more visible.
Especially in the winter months, spider mites can multiply rapidly. The females lay up to 100 pale green to orange eggs on the underside of the leaves, from which the larvae hatch after only 3 days. Within 2 weeks, they continue to develop into reproductive mites.
First aid against spider mites
Spider mites do not like high humidity – this Achilles heel is where you need to hit them:
- Shower infested plants carefully but thoroughly with lukewarm water – including the underside of the leaves!
- Put a transparent plastic bag over the plant and carefully tie it tightly over the pot. This will create a constant warm, moist climate that will cause the spider mites to die. Do not remove plastic wrap until after 10 to 14 days.
- Shower the plant again afterwards to remove any eggs.
Natural sprays against spider mites.
As non-toxic home remedies are suitable two solutions that you can mix yourself:
- spray agent based on rapeseed oil.
Fill 4 parts of water with 1 part of rapeseed oil and a few drops of washing-up liquid as emulsifier into a spray bottle and shake properly. - spraying agent with spirit and curd soap
Mix 1 l of hot water with 30 ml of spirit and 20 g of grated curd soap.
How it works:
Spray infested plants, including the undersides of leaves. Repeat the procedure after 7 days, possibly again after another 7 to 14 days.
Tip: Since not all plants tolerate rapeseed oil, test the rapeseed oil preparation on only one leaf at first and wait a day. Orchids, for example, are sensitive to it.
Even better: Prevent spider mites right away
The best prophylaxis is high humidity around the plants. You can achieve this in several ways:
- Spray the plant regularly with low-lime water – preferably daily.
- Place the pot on a large, low saucer filled with stones. The saucer should always be filled with water without the plant having roots that are wet with water. The evaporating water will provide a moist microclimate.
- If the plants are on the window sill above a radiator, you can place damp cloths on the radiator to increase humidity.
Also, pay attention to care (proper watering amounts and fertilizer applications) and the appropriate location for your houseplants. This is because healthy plants are naturally less susceptible to pest infestation.
The same applies to overwintering potted plants: Here, high humidity and not too warm room temperatures in the winter quarters prevent infestation.