Bring houseplants indoors once overnight temperatures start settling into the low teens Celsius, ideally about two weeks before your area’s average first frost date, and never skip a pest check first — that combination is what keeps a plant that summered on the deck or balcony from turning into an aphid or spider mite problem in your living room all winter. Across most of Canada, that window is opening right now: parts of the Prairies and northern Ontario and Quebec can see their first frost by mid-to-late September, while milder coastal and southern regions may have until October, so early September is exactly the right time to start the process rather than wait for a cold snap to force a rushed move.
The reason this trips people up isn’t the moving part, it’s the timing and the bugs. Move plants too late and a surprise cold night can damage or kill tropical species that have zero tolerance for anything near freezing. Move them too fast, straight from bright, breezy outdoor conditions into a dim, dry living room, and they’ll drop leaves in protest. And skip the pest inspection, and whatever aphids, scale, whiteflies or spider mites have been quietly living on the plant all summer come inside too, with no natural predators or weather to keep them in check, and a small infestation can spread to every other plant in the house within weeks. Getting the sequence right avoids all three problems.
- Watch the thermometer, not the calendar. Most tropical and subtropical houseplants start to suffer once nighttime temperatures drop into the range of about 7 to 13 C, so a good rule of thumb is to plan the move for whichever comes first: nights consistently in that range, or roughly two weeks before your region’s typical first frost date, according to Iowa State University Extension and Penn State Extension.
- Inspect every plant closely before it goes anywhere near your door. Check both the tops and undersides of leaves, along stems, and in the soil for aphids, whiteflies, scale insects and spider mites. The University of Illinois Extension recommends holding a sheet of white paper under the foliage and gently tapping the leaves, then checking the paper for anything that falls off, and also lifting the root ball partway out of the pot to check for insects hiding in the soil.
- Give the plant a bath. Wash the leaves, top and bottom, with a mild dish soap and water solution, then rinse thoroughly, letting some of the soapy water soak into the soil to deal with anything living below the surface. Penn State Extension notes that a strong, steady spray of plain water is often enough to knock off soft-bodied pests before resorting to an insecticidal soap.
- Isolate new arrivals from your existing indoor plants. Set each newly moved plant in its own space, away from other houseplants, for one to two weeks, and check it daily. This quarantine period is what catches any pest that survived the wash before it has a chance to spread, per guidance from the Chicago Botanic Garden.
- Acclimate gradually rather than moving a plant straight from full sun into a dim corner. If you have the lead time, University of Minnesota Extension suggests shifting outdoor plants into a shadier spot in the yard for a week or two before the final move indoors, which softens the shock of the lower light levels they’re about to experience.
- Check the pot and soil while you’re at it. If roots are circling the drainage holes or the plant has clearly outgrown its container over the summer, early fall is a reasonable time to size up, but don’t repot a plant that’s healthy and properly sized just for the sake of it — an unnecessary repot adds stress right when the plant is already adjusting to an indoor environment.
- Adjust your care routine once the plant is settled inside. Indoor air is typically drier and darker than a summer patio, so most houseplants need less frequent watering indoors than they did outside, along with a spot near your brightest window and, if the room runs dry once the furnace kicks in, occasional misting or a pebble tray to add humidity.
None of this is complicated, but the order matters: check for pests before you clean, clean before you isolate, and isolate before you fully integrate a plant back with the rest of your collection. Do it in that sequence in the next week or two, ahead of the first real cold snap, and the houseplants that thrived on your porch all summer should settle into their winter spot with minimal drama — and without bringing any six-legged houseguests along for the ride.
Sources: Illinois Extension (extension.illinois.edu), Penn State Extension (extension.psu.edu), University of Minnesota Extension (extension.umn.edu), Iowa State University Extension and Outreach (yardandgarden.extension.iastate.edu), Chicago Botanic Garden (chicagobotanic.org).
