I found this article by my father in Gardens East, a now defunct magazine he used to write for. It’s timely considering Fall is fast approaching for Northern gardeners like myself. This is a very detailed description of how to bring your houseplants in after spending the summer out of doors. But, truth be told, being laidback gardeners, Dad and I don’t actually follow our own instructions. Unless there’s a major problem, we just grab plants and bring them indoors! Being a laidback gardener sometimes means ignoring best practices and doing what is practical!
If you’re like me, half your houseplant collection spent the summer basking in the warm sunlight and balmy breezes of the real world. Most of them liked it so much, they grew enormously in those few short months. They look vibrant, healthy, strong … but summer Is over and it’s time to get them back indoors!
When to Get Started Bringing in Your Houseplants
Many people err by leaving their plants outdoors too long. Most houseplants are tropical plants and though they appreciate slightly cooler temperatures at the end of the summer, out and out cold is a no-no. It’s not just a question of frost: there are many houseplants that may go dormant (permanently in some cases) if night temperatures start to get into the 40°F (5°C) or even (10°C) range.
Even tougher ones may react badly; after all, increasingly cool evenings, and shorter and shorter days, spell “end of season” to them and they may begin to lose their leaves and flowers early in preparation for winter.
Worse yet, they are often brought indoors just at the beginning of heating season. That means that not only do they go from cool outdoor temperatures to hot indoor ones, but they also go from humid air into dry air: a double whammy!
In Early for an Easier Transition
For most plants, the ideal time to come indoors is when night temperatures have begun to cool off, but are still comfortable… and well before the furnace has begun to kick in. That can be as early as late August or as late as October, depending on local conditions. They should nevertheless all be back indoors by November, no matter how warm fall has been.
There are, of course, exceptions to this rule. Cactus of all sorts—and most succulents too—like it cool and dry in the fall, as those conditions encourage dormancy … and dormancy in turn encourages both healthier growth and flowering. You can safely leave them outside until frost threatens if you can keep them dry. Other plants of subtropical—as opposed to tropical—origin also appreciate cooler temperatures and can stay out a little longer.
Cutting Back Houseplants
That’s all well and good, but what do you do with the schefflera which went from a cute little shrub into a 7-foot (2 m) tree during its summer outdoors? Many plants, in fact, grow like weeds outdoors and often double or even triple in size.
Perhaps the first thing to do is decide if you really need a plant that big. If not, don’t hesitate to prune it back severely. If you follow the first rule (bringing plants back indoors early), the plant will still be in full growth when it comes Inside, so within weeks of pruning, it will begin to fill in any open spaces.
Then, with shorter days and drier air, it should start to slow down for the winter just when it’s looking good. Your goal for the rest of the winter will be to keep it green, but not to stimulate excess growth through overwatering and overfertilizing. With just a little restraint, you’ll keep your plant alive and healthy-looking until spring. Then the longer days can supply it with the light it needs for another good season of growth.
Any top pruning should be followed by a proportionate amount of root pruning. If you’ve only trimmed back the stems slightly, remove a centimeter or so all around the root ball. If you’ve really chopped the plant way back, cut off up to one third of the root ball. When you’ve finished root pruning, put the plant into a slightly larger pot than before. Unless it’s as big as you ever want it to get. In that case, repot into the same size container as the previous one.
If you decide not to prune your plant (you really ought to consider it, though: it does most plants a world of good), you’ll probably still have to repot. Normally, you should only repot into a pot one size larger than the previous one, but this case is an exception. If the plant has nearly doubled in size outside, it’s probably extremely rootbound. Unpot the plant and knock off a bit of soil from around its roots, then loosen them and spread them out so they can occupy more space in their new home. Choose a pot 2 to 3 or even 4 sizes larger than the previous one.
A hibiscus in a 6″/15 pot might well go into an 8″/20 cm pot or even a 10″/25 cm inch one, for example.) Fill the pot with a good growing mix, using a chopstick or pencil to wiggle more soil into the space between the roots. Then water well and keep it out of direct sunlight for few days.
I prefer to repot my plants in late summer, rather than early fall. Mid to late August. That’s when they’re still outdoors. This allows the new plants to grow in faster and reduces transplant shock.
Acclimatization: Hardening Off Houseplants
Growing conditions indoors are far less bright and humid than outdoors. In fact, full sun indoors is about the equivalent of moderate shade outside. When plants are moved indoors, they have to adapt rapidly…and their usual means of doing so is to lose leaves. This leaf loss is, in a sense, perfectly normal. Plants simply can’t use all those leaves in their darker, drier winter home… but that’s no reason to let them go downhill entirely.
When you bring your plants indoors, pick out the sunniest spot in the house as a transition area and grow them there for a week or two. And rev up the humidifier. You’ll want something like 60% humidity as they move in, and not much less than 50% for the rest of the fall and winter. Until spring, maintaining reasonable atmospheric humidity is going to be a major concern. (And no, spraying leaves with water will not help!)
Succulents Are Exceptions
Succulents, such as gasterias, echeverias, cacti and crassulas, are very tolerant of dry air. Just give them regular indoor air: no need to humidify.
For truly humidity-dependant houseplants, usually those with thin leaves and soft stems, like fittonias, polka dot plants, calatheas and spikemosses (Selaginella spp.), you’d do better to give them “greenhouse conditions” for the winter. Cover them with a transparent bag, then put them into their regular winter spot. That will allow humidity on the level of 70 or even 80% or more. The extreme humidity of the air inside a plastic bag is often just the compensation the plant needs to adapt to lower light with minimal leaf loss.
Just seal them inside the bag. Don’t worry, plants produce their own oxygen and carbon dioxide, so they won’t smother! Inside a bag, they’ll use much less water to evapotranspiration, so watering too will be minimal. Talk about making things easy!
Looking for large, transparent bag for a bigger houseplant? Consider re-using bags from the dry cleaner’s. Or using clear trash bag sold for collecting fall leaves.
More Light for Houseplants
Consider the use of artificial light, too. In winter, even the best indoor exposures are barely bright enough to keep most houseplants happy. Supplementary lighting can keep even the most difficult houseplants thriving all winter long.
What About Bugs?
That is probably what worries most people about bringing plants back indoors. However, it’s is rarely a major problem if handled carefully. Most outdoor bugs don’t like it indoors anyway. Besides, they are getting ready for their winter dormancy themselves. At that time of year, they are not very prolific.
That means a little gentle discouragement should keep them outdoors where they belong.
Start by going over the aboveground parts of your plants with a hard spray from the garden hose. You’ll simply wash most insects off. Then sit the pot in a deep basin of water. Make sure the entire root ball is under water (a few rocks might be necessary to hold the plant down). At least 10 minutes… but an overnight soaking won’t hurt the plants. At least, as long as they are allowed to drain thoroughly afterwards. However, bugs certainly don’t like it. Those that don’t drown outright can be picked off the sides of the pots or the plant’s stems as they flee upwards.
Finally, give the entire plant a good spraying with a safe insecticide, such as insecticidal soap, before finally bringing it indoors. A weekly spray for a full month after that should make sure that no unwanted insects or mites make it into your home.
The Final Touch
With lower light, especially combined with drier air, your plants won’t grow as rapidly indoors as they did outdoors, so don’t overfertilize. Indeed, any plants which go semi-dormant in the winter (that is, which stop growing entirely) will need no fertilizer at all until spring. Most plants fall into that category. Those that do show some growth during the off-season will probably find enough minerals to meet their needs from excess minerals applied during the summer. But you might also consider fertilizing them at only a quarter of your usual rate, or quarter as often.
Voila! A little bit of “fall cleaning” now and your summered-out houseplants will be able to make a perfect transition to their winter home!