Pruning Pelargoniums, commonly known as geraniums, is important for gardeners who wish to preserve these tender annuals through the winter months. Geraniums, which are perennial in warmer climates, will not survive the freezing temperatures typical of most temperate zones. Cutting them back and preparing them for dormancy or reduced growth indoors ensures survival. This process focuses the plant’s energy reserves, allowing for a strong root system and robust growth when returned outdoors the following spring.
Determining the Ideal Time for Pruning
The timing of your geranium pruning is determined by local weather conditions rather than a set calendar date. The goal is to act before the first hard freeze, which is a drop in temperature severe enough to freeze the water within the plant’s cells and cause tissue damage. A light, brief frost may cause some leaf discoloration, but it generally does not harm the plant’s core structure.
Monitor forecasts closely for temperatures consistently approaching 32°F (0°C), the threshold for a damaging freeze. Beginning the pruning process just as the days shorten and temperatures dip consistently below 45°F (7°C) allows the plant to naturally slow its growth rate. This late fall window gives you time to prepare the plant without the stress of an immediate weather emergency.
Essential Pruning Techniques
Begin the pruning process by gathering your tools, specifically a pair of sharp bypass pruners. Sterilize the blades with a diluted bleach or alcohol solution before use to prevent the transfer of fungal or bacterial pathogens to the fresh wounds of the geranium. This step minimizes the risk of infection when the plant is under stress in its winter quarters.
Pruning involves cutting back the plant significantly, typically removing between one-third to one-half of the overall growth. The objective is to eliminate soft, green, or woody, leggy stems that tend to become brittle and unattractive over the winter. Make each cut just above a visible leaf node or a joint where a leaf or stem branches off the main stalk.
Cutting directly above a node ensures the remaining stem section has a viable point for new growth in the spring. Aim for a clean, angled cut that promotes rapid callousing and minimizes the surface area for potential disease entry. For bare-root storage, a more severe cut down to about 6 to 8 inches of firm, woody stem is recommended to minimize the plant’s surface area. After trimming the stems, remove all remaining leaves and spent flowers, as this decaying material can harbor mold and pests during storage.
Immediate Steps Following Pruning
Once the stems are trimmed, the plant requires a thorough inspection before moving indoors. Carefully check the undersides of the remaining leaves and stem crotches for common pests like aphids and spider mites, which multiply rapidly indoors. Infestations should be treated with an insecticidal soap or horticultural oil before the plant is placed near other houseplants.
For plants intended for dormant storage, gently dig them up from the garden bed and shake the soil free from the root system. Allow the exposed root ends to dry or callous for a few days in a shaded, protected area. This drying period develops a protective layer over the wounds, helping prevent rot and mold during storage.
If you plan to keep the geranium as a winter houseplant, repot it into a container that comfortably accommodates the root ball, using fresh, sterile potting mix. Regardless of the overwintering method chosen, reduce watering significantly in the days following the cutback. Less water signals to the plant that it is time to slow down its metabolic processes and prepare for rest.
Overwintering Methods
One method is dormant storage, best suited for plants pruned hard and largely cleared of soil from their roots. These bare-root plants should be placed in a cool, dark, and dry location, such as a basement or unheated garage, where the temperature consistently remains between 45°F and 55°F (7°C–13°C). They can be stored in open paper bags or hung upside down from the rafters to allow for air circulation.
Plants in dormant storage require minimal maintenance, often needing just a light misting or a brief soaking of the roots in water for an hour once a month to prevent complete desiccation. An alternative is the active growth method, where the pruned geranium is treated as a houseplant. Place the potted plant in a bright, sunny, ideally south-facing window to receive maximum light exposure.
For active growth, maintain a cooler room temperature, preferably around 60°F to 65°F (15°C–18°C), and water only when the top inch of soil is completely dry. This cooler temperature and reduced watering prevents the plant from becoming spindly or “leggy” due to low winter light levels. While the plant may not flower, it will remain alive and ready to resume vigorous growth once spring arrives.