Harmful insects Houseplants

How to Debug Your Plants… Before You Bring Them Back Indoors

Tray of houseplants read to bring in for the winter.

By Larry Hodgson

Are your houseplants spending a summer outdoors? So much the better, because they usually benefit enormously from the experience, but you also have to know how to bring them back inside … without unwanted insects.

When the nighttime temperature begins to drop seriously, to below 55 °F (13 °C) most nights, it’s time to bring back indoors the houseplants you placed outside for the summer. True enough, most could theoretically tolerate even greater cold, even up to frost in several cases, but plants respond best to the transition when you do it while nights are still relatively warm. If you wait for frost to threaten, the shock of moving from a cold environment (outdoors) to a warm, dry one (indoors) often leads to massive leaf yellowing and loss if not flower drop.

That’s why it’s best to start fairly early in the fall, even if the weather still seems reasonably warm to you. This is especially in colder areas, but even in a fairly mild climate, there comes a time when it’s just too cool for tropical plants to be outdoors. Unless you live in the tropics, of course, where garden plants and houseplants are pretty much the same thing.

Bring in the Plants, Not the Bugs

Of course, bringing plants in from the great outdoors into your house presents a dilemma. How to do so without bringing in unwanted insect pests at the same time? Fortunately, that’s surprisingly easy to do. Here’s how:

Houseplant surrounded by soapy water and cleaning products.
Start by washing the plants well. Ill. Claire Tourigny

First, give the plants a thorough rinse with a strong spray of water from the hose. In fact, that’s really all you need for many plants.

For plants that you know are susceptible to insects, like fuchsias and pelargoniums (whiteflies love them!) or hibiscus and palms (prey to spider mites), water alone won’t be enough. Spray them thoroughly with a solution of insecticidal soap (avoid dishwashing soap: it can be toxic to plants). A rate of 1 teaspoon per quart of water (5 ml per liter) will do.

If you suspect the plant is infested with something more serious, such as mealybugs or scale insects, wash the whole plant leaf by leaf, making sure you reach both sides of the leaf, plus the stems and even the leaf axils, with a cloth soaked in soapy water, then rinse well.

Soil Insects

But what to do with the insects and other critters that can hide in the plant’s soil? Most are not really harmful to plants, but you still won’t want to bring them indoors for the winter.

Plant soaking a tub of soapy water.
Soak the pot in soapy water to remove any insects living in the soil. Ill. Claire Tourigny

To get rid of them, immerse the pot in a large bucket of soapy water. You can use a more diluted solution for this, about ¼ teaspoon per quart of water (1 ml per liter), so as to avoid root damage. Now let the root ball soak for 15 to 30 minutes. You may need to put a brick or rock on the top of the root ball to hold it under water. The combination of several minutes of immersion in water and the presence of insecticidal soap will kill even the toughest insects.

This soaking can be a bit messy, as ingredients in the potting mix tend to float free and stick to the stems and lower leaves, but you’ll deal with that a bit later.

When the root ball has soaked for the required time, remove the pot from the solution and let it drain very well. Now, wipe any soil or litter from the pot and the plant and bring your clean, debugged plant back into the house.

See? It wasn’t that hard!

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.

7 comments on “How to Debug Your Plants… Before You Bring Them Back Indoors

  1. What a timely post Larry! The weather in Calgary is beautiful this week and the temptation is to leave my plants out a bit longer. I don’t want to shock my plants, so I’ll follow your tip regarding the change in temperature from outside to inside and start bring the plants in now. Also, I appreciate your advice to soak the entire pot in a tub of soapy water – I’ll be trying that today! Thanks!

  2. Good advice about soaking the whole root ball in soapy water. Always seem to get little ants taking up residence in my succulents.

  3. Thanks for the timely reminder! What kind of soap to soak the pot and soil in?

  4. Mary Ann Witcher

    Spiders are horrible this year, any tips in addition to the blog post?

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