The vibrant plants commonly called geraniums are technically Pelargoniums, tender perennials originating from South Africa. Because these plants cannot tolerate frost, they are typically treated as annuals in cooler climates and die off with the first hard freeze. Overwintering potted Pelargoniums is a simple and cost-effective way to preserve favorite varieties, allowing them to return with renewed vigor the following spring. This process involves preparing the plant for a period of reduced activity until the outdoor growing season resumes.
Preparing Plants for Indoor Storage
The preparation process must begin before the first heavy frost, usually in early to mid-fall, to prevent cold damage. The first step involves hard pruning the plant by cutting back the stems by about one-third to one-half of their current length. This reduction helps the plant conserve energy and makes the containers easier to manage indoors. Removing excessive foliage also lowers the risk of fungal diseases developing in cooler, less ventilated storage areas.
Before moving the pots inside, inspect thoroughly for pests like whiteflies or aphids, as these can quickly infest indoor spaces. Any signs of insects or moldy growth should be removed or treated with horticultural soap. Finally, clean the pots and clear away any debris or dead leaves on the soil surface. This hygiene is important because organic matter can harbor moisture and pathogens that thrive in confined indoor conditions.
Choosing the Right Overwintering Method
The choice of method depends on the space, light, and temperature conditions available.
Semi-Dormant/Potted Storage
This technique requires placing the entire potted plant in a cool, bright location, such as an unheated sunroom or a garage window. The Pelargonium remains in its container and continues slow growth throughout the winter, requiring temperatures between 45°F and 65°F (7°C and 18°C). This approach is ideal for those who want a plant that will start the spring season already actively growing.
Dormant/Bare-Root Storage
This method is suitable for maximizing space and is chosen when a cool, dark location is available. For this technique, the plant is removed from its pot, the soil is shaken off the roots, and the plant is pruned back significantly. The bare-root plants can be stored in a paper bag, a cardboard box, or hung upside down in a dark, dry, and frost-free area, ideally maintained between 45°F and 55°F (7°C and 13°C). This technique forces the plant into a deep rest, relying on the stored energy in its thick, succulent-like stems for survival.
Maintaining Geraniums During Winter Dormancy
Once plants are settled, the focus shifts to environmental control, particularly temperature and moisture. Whether stored bare-root or potted, Pelargoniums tolerate cool conditions but must be kept above freezing, with temperatures maintained above 40°F (4°C). Keeping the temperature too warm encourages excessive, weak, or “leggy” growth due to insufficient winter light.
For semi-dormant, potted plants, watering must be drastically reduced compared to the active growing season. Allow the soil to dry out almost completely between light waterings, typically only once every few weeks, to prevent root rot. Bare-root plants stored in a deep dormant state require minimal moisture, sometimes needing a light misting or a quick root soak every four to six weeks to prevent the stems from shriveling. Maintaining air circulation is important for both methods, as stagnant air increases the likelihood of mold and fungal diseases.
Regular monitoring is necessary throughout the winter to check for common problems. Inspect stems and roots for signs of mold, rot, or dehydration. If a bare-root plant shows signs of shriveling, a short soak of the roots in water for an hour can rehydrate the plant before it is returned to storage. Promptly removing any soft, rotting, or diseased material ensures the problem does not spread.
Transitioning Plants Back Outdoors in Spring
Reviving overwintered Pelargoniums begins approximately six weeks before the last expected frost date. Bare-root plants should first have any dried or shriveled stems pruned back to the firm, green tissue. These specimens should then be potted into fresh, well-draining potting mix after soaking their roots in water for a couple of hours to rehydrate them.
All overwintered plants benefit from repotting into fresh soil, as the existing medium is often depleted of nutrients or compacted. Placing the newly potted plants in a bright, sunny location initiates the break from dormancy, and watering should begin to increase gradually. New growth should emerge within a few weeks, signaling the plant is actively recovering.
The final step is “hardening off,” which prepares the plants for the outdoor environment. This involves gradually exposing the plants to increasing durations of direct sun and wind over seven to ten days. Once the danger of frost has passed, the fully acclimated Pelargoniums can be moved back to their permanent outdoor locations.