How To Debug Plants Before Bringing Them Indoors

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Robert Pavlis

Growing marginally hardy or non-hardy plants in cold climates usually involves growing them in containers and moving them indoors before winter. Everyone loves to see houseplants flourish when grown outside during warmer months – but no one likes bugs hitchhiking back inside! Fortunately, there are ways to remove unwelcome insects before they enter your home.

How To Debug Plants Before Bringing Them Indoors
How To Debug Plants Before Bringing Them Indoors, Credit: Vadim Kaipov

When to Bring Plants Indoors

The goal of moving vulnerable container plants indoors is to prevent damage from frost and cold stress. The best time to do this depends on where you live and the plants in question. A safe rule of thumb is to move your plants indoors before the temperature drops below 50 F (10 C). Many plants can take a temperature as low as 41 F (5 C), but under no circumstances should plants be exposed to the first frost.

It is best to give plants time to adjust to indoor conditions because a sudden change in light, temperature or humidity can be stressful and they’ll drop leaves or flowers. Putting plants indoors overnight for the first few days is a good start. Over the course of a week you can gradually increase the time your potted plants spend indoors until they can remain inside for the entire day. Many people bring them in on really cold nights and take them back out during the warmer days.

If you take your plants in and out each day, try to keep them separate from other indoor plants so pests don’t infect them. A sunroom or garage work well for this.

Microbe Science for Gardeners Book, by Robert Pavlis

Once you are ready to bring them in full time, follow these steps.

  1. Repot if needed
  2. Spruce up the leaves
  3. Soak the soil
  4. Clean the pot
  5. Spray the leaves

Repot if Needed

If the soil is old or has white salt deposits on it, consider repotting now. Root bound plants can also be repotted. You might as well keep all the dirt outside and you get rid of any pests in the soil at the same time.

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Spruce up the Leaves

Remove any dead or unsightly leaves. Clean up any old flowers laying on the soil. These can all trap insects.

While you are checking your leaves, look for signs of bugs. Signs of infestation to look out for include egg sacs under leaves, webbing, and leaves that are chewed on, holey, misshapen, speckled, yellowed, or mottled. Some insects like aphids, scales, whiteflies, and mealybugs produce a sticky substance called honeydew, so look out for any leaves that are sticky or unusually shiny.

Soak the Pot to Debug the Soil

Take a pail and add enough water so that you can set a plant in it and have the water cover the pot. Add a soap to the water.

The best soap option is insecticidal soap. It is both effect and safe to use on plants.

Many people use dish soap and this can work too, but it is more likely to harm your plants because these are really detergents. Even so called safe soaps like Castile soap and liquid hand soap can be harmful to plants. They probably harm roots less than leaves, but insecticidal soap is the best. If you want to use something else, stay away from dish soaps and use a liquid hand soap.

Place the plant in the soapy water and soak for 20 minutes.

Many insects will crawl out so they don’t drown and smaller one drown. Remove any you see floating in the water.

At the end of the soak, water the soil well to remove most of the soap. Let the pot sit to drain.

Clean the Pot

If the pot is dirty, has hardwater buildup on it, or moss is growing, now is a good time to clean the pot.

Spray the Leaves for Bugs

Even if you don’t see any bugs, their eggs could be hiding in small cracks between leaves, ready to hatch in the warm indoor temperatures. It is a good idea to spray the whole plant.

There are may DIY products like dish soap, hand soap, Castile soap, Neem etc., but the safest option is insecticidal soap. Unlike other products it is a potassium salt of fatty acids which is the least detrimental to plants.

Some plants, like palms and ferns, are more sensitive to insecticidal soap. To be safe, you can do a test by spraying one or two leaves with properly prepared insecticidal soap spray. Wait a day or two to see if the plant shows signs of damage – if not, you’re good to go. Avoid using on newly established transplants, cuttings, or plants under drought stress.

To work, insecticidal soap needs to contact the insect or eggs, so make sure you spray all surfaces of the plant including the underside of leaves and any small cracks.

Pests that cling to your plants, like scale insects, are more difficult to get rid of. You can soak a cloth with insecticidal soap and wiped down each leaf and stem.

The Best and Cheapest Insecticidal Soap

A lot of people use soap from around the house because they think it is cheaper. Buying insecticidal soap in spray bottles is more expensive but there is a way to buy good but cheap insecticidal soap. Buy in bulk.

There is very little difference between brands of different insecticidal soap, so buy the one that is offered in bulk, like this Safer’ Insecticidal Soap. A good quality insecticidal soap has 1% potassium fatty acids in it. The bulk material is 50%. So a 500 ml bottle will make 50 L (50 refills in a standard spray bottle) at about $0.50 per bottle. I bet your liquid hand soap is more expensive.

bulk insecticidal soap
Example of bulk insecticidal soap

Here are some affiliate links for bulk insecticidal soap on Amazon.

Woodstream Safer Insecticidal Soap 

Fertilome Natural Guard (40704) INSECTICIDAL SOAP

Are There Alternatives to Insecticidal Soap?

While insecticidal soap is the most popular method for debugging plants, some gardeners are wary of its “chemical” nature and suggest alternatives like alcohol solutions, yellow cup traps, sticky traps, neem oil, garlic cloves or oil,  and more. Unfortunately, many of these alternative debugging methods simply don’t work or end up doing more harm than good.

Highly Infected Plants

The above procedures work quite well to get rid of most bugs on your plants. If you find a heavily infested plant it is a good idea to follow the above steps, but keep plants outside after spraying for bugs, for another couple of days. Then spray the leaves a second time. That way you have a better chance of catching newly hatched bugs.

Bringing Plants Indoors

The light level indoors is much lower than outside, even if you place them under lights. The lower light will stress them and they will start to grow slower. To compensate, water and fertilize less, but give them the best light you can.

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Written by Marika Li

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

2 thoughts on “How To Debug Plants Before Bringing Them Indoors”

  1. 7 months ago my bride & I moved to east Tennessee, a little west of Johnson City, close to Greeneville. The humidity is moderately high and the ground is usually wet from dew virtually every day. My issues include, but not limited to, slugs & grubs. I know I’ll have many questions as time goes by, but right now I need to know how to eradicate the slugs in and around my raised beds. They “attacked” (at night, of course) my watermelons. My bride wants me to plant watermelons next year with trellises. I’ll have to look into that. I know salt works on slugs, but that doesn’t seem to be the solution with my tomatoes, peppers, etc.., as salt will destroy my food. Thanks for “listening.”


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