Spider mites can be a plague. When one container plant becomes infected with spider mites, all of your container plants are at risk. Unfortunately, it's very very difficult to eradicate spider mites.
Sometimes, your only recourse is to discard infected plants. If you have to discard an infected plant, do not put it into your compost pile. The best way to dispose of the plant is to place it in a paper or plastic bag and put it into the trash.
Identifying a Spider Mite Infestation
Spider mites are tiny—smaller than the head of a pin—so it's difficult to see them. To test a plant for spider mites, hold a plain white sheet of paper underneath or near the plant and tap on the foliage several times, Examine the paper for creatures that are dislodged and crawling around on the paper. Spider mites can range in color from red to light brown, yellow, or green.
Symptoms of spider mite infestation is a white stippling on the leaves, or foliage that has a faded, yellow or grey cast. Severely infested plants are covered in white webbing particularly at the intersection of branches.
Steps to Battle Spider Mites
Like most plant pests, you have a much better chance of eradicating spider mites if you discover them before an all-out infestation breaks out. The more mites, the more eggs, and the harder it is to control them.
The first line of defense with almost any insect problem is to spray the plant with a strong stream of water from a garden hose to wash away as many insects as possible. Make sure to spray the undersides of the leaves as well as the tops. Repeat the rinsing treatment frequently to ensure the mites will not climb back up the plants. This approach might not be completely effective for heavy infestations.
You can also use an insecticidal soap spray to kill any remaining insects. With large plants, it's not easy to achieve adequate coverage over the entire plant, including the undersides of leaves, but do the best you can. Insecticidal soap is preferred over a pesticide because it is acceptable for organic gardening. Note that other insects and pollinators that are directly sprayed will be harmed in the process.
After using insecticidal soap, try neem oil or a neem oil combination. A disadvantage of neem oil is some people don't care for its fragrance and it can be sticky if it lands on walls and furniture.
Be aware that if you are spraying outdoor plants with soaps and horticultural oil to control mites, do so only when temperatures are cooler than 85° Fahrenheit. Spraying when temperatures are higher than 85° can damage plants.
You can also try a pyrethrin insecticide, which is somewhat more toxic than neem oil and insecticidal soap. It is classified as a natural pesticide because it is made from chrysanthemums.
Chances are you will have to continue to spray your spider mite-infested plant every seven to 10 days in order to interrupt the cycle of eggs hatching. Also, make sure to spray the soil as well as the entire plant.
There is no absolute recommendation about when to dispose of an infected plant unless it is completely dead. Even then, plants can surprise you and bounce back. You can battle spider mites over the winter and cut back the plants severely in the spring, then move the plant outdoors for the summer. Some plants can rebound and thrive outdoors. However, at the end of the season when you bring the plants indoors, the mites can return with a vengeance.
How to Prevent Spider Mites
Prevention is always the best option. Before you purchase any plant, look for the telltale signs of white stippling on leaves or webbing. If you see any indication of mites, don't buy the plant or any plants that are nearby.
Spider mites like dry and dusty conditions, so keep your plants hydrated with a good amount of humidity. These conditions are inhospitable to mites.