When nights start to cool in the fall, it’s time to move your tropical plants indoors. Cold damage can set in when temperatures fall below 45 to 50 degrees, depending on the plant. 

But when it’s time to bring them inside, a quick wipe-down of the leaves isn’t enough to keep the bugs outside. 

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Pests often live in the soil and can hitch a ride in the pot. Some of the most common sources of fungus gnats and other houseplant pests are when outdoor plants are brought indoors in the fall. And a pest problem in one plant can become a problem for the rest of the plants in your house.

Before the plants come inside

Give your plants a bath before bringing them inside. Some experts recommend soaking plants in a bucket of water with mild dish soap. The soapy water should reach the soil because it helps kill pests living there. Make sure to wash the outside of the pot as well. 

If the plant is too big for a bucket, spray it with water to remove dust and soft-bodied insects. Then wash the tops and undersides of the leaves with soapy water and rinse. Again, make sure the soapy water gets into the soil.

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Don't rush the move. Abrupt changes can cause yellowing leaves, wilting, dieback or even death. Start the plant in a very sunny window, then slowly reduce its sun exposure.

Once the plants are inside

Keep the outdoor plants away from any other indoor plants for a while. It helps to isolate and monitor these plants for fungus gnats or other insect activity before introducing them to other plants; this makes sure no pests spread to other plants.

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Cutting back on watering is often the most important step in dealing with fungus gnats. Letting the soil dry between waterings decreases the larvae's survival because they thrive in moist soil.

Check your plant's needs first because tropical plants vary in how much water they can handle. But in general, watering less often will help kill those pests.

Every time you water the plants, check for pests. If you spot any, you can use more insecticidal soap on the plant until the problem is resolved.