Just recently I explained how to bring houseplants indoors while leaving their insect pests outdoors. And while doing so, I stressed the importance of bringing houseplants indoors early, ideally at the beginning of September. That’s because the vast majority of houseplants are of tropical origin and don’t appreciate the gradual cooling that comes with fall. They prefer to be brought back indoors before fall nights start to cool off.
Well, there are exceptions to every rule.
There is a small minority of houseplants that are not tropical plants, but of subtropical origin. In other words, in their native environment they experience cool to very cool temperatures part of the year, yet without having to tolerate frost. These plants, unlike most others, prefer to spend the autumn outside and most will readily tolerate temperatures as low as 33˚F (1˚C). Therefore bring them in only when frost is announced. In fact, if there is an early frost, it’s sometimes best to bring them in overnight, then to put them back outdoors for yet a few more weeks, until frosty nights truly become the norm.
Even when you do bring these plants indoors, trying keeping them in a cool place, with nights below 60˚F (15˚C) during the winter, if you can. They’ll really appreciate it!
In this category you’ll such plants as indoor azalea (Rhododendron simsii), some orchids (including Cymbidium), Christmas cactus (Schlumbergera spp.), most other cacti, and lily of the Nile (Agapanthus). Leaving these plants outdoors for a few extra weeks even tends to encourage better flowering when they do come back indoors.