Laidback Gardener Tip of the Day

When Spider Mites Invade Houseplants

20151024A
Specks of dust that move are most likely spider mites.

Spider mites (or red spider mites), Tetranychus urticae, are everywhere: on our outdoor plants in the summer and on our houseplants in the winter. Despite their common name, they aren’t really spiders, but rather type of mite. They are tiny pests you can barely see with the naked eye. In fact, they look like specks of dust, but specks of dust that move. You’ll need a magnifying glass to see them clearly. When you can see them up close, they may be red, as the name red spider mite suggests, but are more likely to be beige or green and often (but not always) marked two dark spots.

20151024D
Spider mites under a magnifying glass.

Spider mites damage plants by piercing their leaves and stems and sucking the sap that flows from the wound. This causes a slight yellowing of the plant that increases over time. At first, you might not be able see the pests themselves. Try placing a sheet of white paper under discolored leaves. Tap the leaves, then watch for tiny moving creatures on the paper. Those are spider mites.

Most people don’t notice spider mites at that stage, though. They realize they have a problem when they start to see webbing much like the kind a spider produces forming between the leaves and along the stems. Think of these webs as highways allowing spider mites to travel rapidly from one part of the plant to another. They also serve as protection against their enemies, including humans. And when you look at the webbing, there are plenty of tiny moving critters. Oops! This means your plant is not just lightly infested, but seriously so and in fact, in danger of dying.

Spider mites are present on houseplants throughout the year, but are rarely noticed as long as they are few in number. But the population explodes under certain conditions, especially when the air is hot and dry. That’s why spider mites appear out of nowhere on our houseplants in late autumn and winter: when you start heating a house, its atmospheric humidity drops precipitously. In many homes, the air in winter is drier that that of the Sahara Desert! And spider mites just love dry air!

What houseplants are attacked? Probably most can be, but in fact a lot of plants will support a small population of mites without any noticeable damage. It is mostly plants with thin leaves that suffer visibly from spider mites: bananas, brugmansias, calatheas, crotons, hibiscus, impatiens, English ivies, palms, scheffleras, etc.

284.K
You can’t beat a good shower for controlling spider mites.

To control spider mites, first give them a thorough washing, either in the shower or with a damp soapy cloth. You have to remove the webs first or your other treatments won’t be effective: spider mites will be out of range of pesticides behind their webs. When the webs are gone, then you can spray with insecticidal soap, neem, pyrethrin, etc. if you want, but… my experience is that a thorough shower or washing, regularly repeated, is usually all you need to get rid of spider mites… temporarily. If the air remains hot and dry, though, they will be back!

20151013C
Humid air keeps spider mite populations down.

So, to really solve the problem, you need to change the conditions in the room where you grow your houseplants. First, if you can, lower the temperature in the room, especially at night (the cooler the air, the less quickly spider mites reproduce). Even more importantly, do whatever you can to increase the atmospheric humidity. Moist air alone will not cure an infestation (once established, spiders continue their attack in spite of the improved conditions), but it will prevent their return. Therefore, a room humidifier is often the best prevention possible when it comes to spider mites!

Larry Hodgson is one of Canada’s best-known garden communicators. He has notably been editor-in-chief of HousePlant Magazine, Fleurs, Plantes et Jardins, À Fleur de Pot and Houseplant Forum magazines and is currently the garden correspondent for Le Soleil and radio garden commentator for CKIA-FM Radio. He has written for many garden publications in both the United States and Canada, including Canadian Gardening, Harrowsmith, Horticulture, Fine Gardening and Organic Gardening. He also speaks frequently to horticultural groups throughout Canada and the U.S. His book credits include The Garden Lover’s Guide to Canada, Complete Guide to Houseplants, Making the Most of Shade, Perennials for Every Purpose, Annuals for Every Purpose, and Houseplants for Dummies, as well as nearly 60 other titles in English and French. He is a past president of the Garden Writers Association (now Garden Communicators International) and the winner of the prestigious 2006 Garden Media Promoter Award offered by the Perennial Plant Association. He resides in Quebec City, Quebec, Canada.

10 comments on “When Spider Mites Invade Houseplants

  1. Pingback: Longer Days Awaken Pests | Laidback Gardener

  2. Pingback: Don’t Kill Those Red Mites! | Laidback Gardener

  3. Pingback: Help! My Hibiscus is Losing its Leaves! – Laidback Gardener

  4. Pingback: A Rosemary Christmas Tree: Doable, But… – Laidback Gardener

  5. Pingback: One Living Christmas Tree That Really Thrives Indoors – Laidback Gardener

  6. Pingback: The Little Palm Tree that Could – Laidback Gardener

  7. Pingback: Controlling Spider Mites in the Garden – Laidback Gardener

  8. Pingback: Miniature Roses: Better Off in the Garden – Laidback Gardener

  9. Pingback: Higher Humidity Means Happier Houseplants – Laidback Gardener

  10. Pingback: 15 Not-So-Easy Houseplants – Laidback Gardener

Leave a Reply

Sign up for the Laidback Gardener blog and receive articles in your inbox every morning!

%d bloggers like this: