Okay, it may still seem hot and summery outdoors, but for how long?
Early September is the ideal time to bring the houseplants you placed outside for the summer back inside. For a smooth transition, you’ll want to do this when the nights are still warm. If you wait until the nights start to become chilly, the plants will become acclimated to that and may react badly when brought back suddenly into the warmth, losing leaves and flowers. It’s better to make the transition between outdoors and in when the conditions in both environments are essentially identical… and in many climates, that’s early September.
Of course, there are a few exceptions, houseplants that are more subtropical than tropical and that therefore actually enjoy cool to cold (but not freezing) temperatures in the fall. You can leave these out until frost truly does threaten. For more on the subject, read Some Houseplants Like It Cold.
If the plant has grown considerably over the summer, you might want to prune it back before you bring it back inside… or to repot it into a larger pot.
And in some circumstances, it’s easier take cuttings and bring them indoors rather than the whole plant.
Rinse your plants thoroughly with a fairly strong jet of water to get rid of dust, grime… and most bugs. Then, to make sure you got all the critters, spray both sides of the leaves with insecticidal soap.
So much for the foliage. To eliminate the insects hidden in the soil, plunge the pot into a tub of soapy water, and soak the roots for 15 to 30 minutes (use rocks or bricks to hold the pot underwater). Soap is toxic to insects, but does little to no damage to the roots, so the treatment should dispose of any unwanted underground intruders.
Next, let the pot drain and bring the plant back in. Yes, it’s that easy!