Moving potted plants indoors for the colder months is necessary to ensure their survival and health. Most container plants cultivated outdoors are not native to temperate climates and cannot withstand seasonal cold. Accurately timing this transition is crucial. Moving plants too late exposes them to damaging low temperatures, while moving them too early can prevent them from benefiting from the last warm weather and outdoor light. The goal is to identify the precise temperature threshold that signals the end of the outdoor growing season for your collection.
The General Safety Cutoff
For most common potted plants, especially those treated as annuals or houseplants, the safety threshold is a nighttime temperature of 50°F (10°C). This temperature represents the point where tropical and subtropical species begin to experience significant physiological stress. Waiting until temperatures consistently drop below this mark risks exposing the plant to chilling injury.
Chilling injury is a form of cold damage that occurs at temperatures well above the freezing point, typically between 32°F and 55°F (0°C and 13°C). Within this range, the plant’s cellular membranes lose their fluidity and become rigid. This change impairs the membrane’s ability to regulate the passage of water and nutrients, leading to cellular dysfunction.
Visible symptoms of chilling injury include wilting, discolored patches, and eventual tissue collapse, which can appear days after cold exposure. The root system’s ability to absorb water and essential minerals is also significantly reduced. To prevent this internal damage, complete the move indoors before the weather forecast predicts consistent overnight lows in the 45°F to 50°F (7°C to 10°C) range.
Varying Temperature Needs by Plant Type
The specific timing for the indoor move depends on the plant’s natural environment and hardiness. Tropical and Tender Plants must be prioritized for the earliest move, ideally when nighttime temperatures consistently fall below 55°F (13°C). These plants, which originate from equatorial regions, are the most susceptible to chilling injury.
Examples such as Ficus species, citrus trees, tropical hibiscus, and basil are sensitive to cold-induced stress. Leaving them out even for a few nights below 50°F (10°C) can trigger massive leaf drop or permanent damage to growing tips. These plants require early shelter to maintain their metabolic processes.
Semi-Hardy Plants possess a greater tolerance for cooler conditions and can remain outside until the nighttime lows approach 40°F to 45°F (4°C to 7°C). This group includes species like geraniums (Pelargonium), coleus, and hardier herbs such as rosemary and thyme. While they may cease active growth, they can withstand these temperatures without immediate cellular damage.
These plants often benefit from the longer exposure to outdoor light, but they must be brought in before the general safety cutoff. Dormant and Hardy Plants, such as certain bulbs, can often withstand a light frost and may only need to be moved just before a hard, sustained freeze. This group is typically moved for storage in a cool, dark location rather than being treated as a houseplant, requiring minimal attention and water through the winter.
Practical Steps for the Indoor Transition
Once the temperature signals the time for the move, several preparatory steps are necessary to ensure the plant’s health and prevent indoor infestations. The first step is a gradual acclimation process to ease the plant’s adjustment to the lower light levels inside your home. This involves moving the potted plant to a shadier location outdoors for about one to two weeks, minimizing the shock of reduced light intensity.
During this period, begin the physical transition by bringing the plant indoors for the night and returning it outside the following morning. This cycle, repeated over several days, allows the plant to slowly adapt to the indoor temperature and humidity while still benefiting from the fresh outdoor air. A sudden move from full sun outdoors to a dimly lit living room can cause severe leaf burn or rapid leaf drop.
A thorough pest inspection and treatment is necessary before any plant crosses the indoor threshold. Outdoor conditions often lead to hitchhikers like spider mites, aphids, or fungus gnats, which can quickly spread to existing indoor plants. Inspect the undersides of leaves, the crevices where stems meet the soil, and the area between the pot and the saucer.
To eliminate pests, wash the foliage with a strong stream of water, focusing on the undersides of the leaves. For intensive cleaning, apply insecticidal soap or horticultural oil while the plant is still outside. Finally, pruning should be done to reduce the plant’s overall size, removing any dead, diseased, or excessively long foliage. This reduction helps the plant manage lower indoor light and humidity during its winter resting period.