The vibrant flowering plants commonly known as geraniums are generally not cold-hardy and cannot survive freezing temperatures outside. These popular garden plants are technically Pelargoniums, which are tender perennials treated as annuals in most climates, rather than the true, hardy Geranium species (cranesbills). Preparing these plants for winter is an act of preservation, shifting the plant from active growth to a state of temporary rest or reduced metabolism. This intervention is necessary because Pelargoniums originate from warmer, subtropical regions and lack the genetic mechanisms to withstand a hard frost.
Timing and Initial Preparation
The preparation process must begin before the first hard frost arrives, typically in late fall when nighttime temperatures consistently drop below 40°F. Waiting until the last minute risks damage to the plant’s tissues, which cannot tolerate freezing. Bringing potted specimens indoors or digging up garden plants is the first step in protecting them from cold stress.
Before cutting or storage, a thorough inspection of the plants is necessary for good sanitation. Check all leaves and stems for signs of pests such as whiteflies, spider mites, or aphids, which can easily infest other houseplants during the winter. Any visibly damaged, diseased, or yellowing leaves should be removed entirely to minimize the risk of fungal issues developing during storage.
The Pruning Procedure
Once the plants are prepared and inspected, the physical act of cutting back can begin to conserve the plant’s energy during its dormant or semi-dormant state. Use sharp, clean tools, such as pruning shears, to ensure a smooth cut that heals quickly and reduces the chance of introducing pathogens into the wound. Wiping the blades with a disinfectant solution between plants helps maintain hygiene.
The goal of pruning is a significant reduction in size to lower the plant’s winter energy demands. Cut back the stems by one-half to two-thirds of their existing length, leaving only four to eight inches of stem above the soil line. When making each cut, aim just above a leaf node, which is the slightly swollen area where a leaf or bud emerges from the stem.
Cutting above a node encourages the plant to produce new, healthy growth when revived in the spring. This reduction allows the plant to focus resources on maintaining the woody structure and root system rather than supporting extensive, soft growth. The removed green stem tips can often be saved and used to propagate new plants.
Choosing an Overwintering Method
Once pruned, the geraniums must be stored using a method that suits the available space and temperature conditions.
Bare-Root Dormant Storage
One common technique is dormant storage, often called the bare-root or hanging method, which aims for a deep rest period. For this method, gently remove all soil from the roots of the pruned plant and place the bare roots into a paper bag or hang the entire plant upside down. The storage area needs to be dark, dry, and consistently cool, ideally maintaining a temperature range between 40°F and 50°F.
Temperatures above this range encourage mold or premature growth, while freezing temperatures destroy the plant’s tissues. The plant will naturally shrivel and lose most of its remaining leaves during this time, but the roots should be checked monthly and lightly misted with water or briefly soaked for an hour if they appear excessively dry or brittle.
Semi-Dormant Potted Storage
The second method involves semi-dormant potted storage, which requires more space and light. The pruned plant is kept in its pot, or repotted if dug from the ground, and moved to a cool, bright location such as a garage with a window or a cool sunroom. The temperature should be slightly warmer than bare-root storage, but still cool enough to slow growth significantly.
Watering is greatly reduced, with the plant receiving only enough moisture to prevent the soil from drying out completely, perhaps once every few weeks. This state keeps the root ball alive but limits top growth, preventing the plant from becoming weak or “leggy” due to low winter light levels. A third option is to grow the Pelargonium actively indoors as a houseplant, which requires high light levels, possibly supplemental grow lights, and a consistent temperature around 60°F to 65°F.
Spring Revival and Replanting
The transition out of winter storage should begin approximately six to eight weeks before the last expected spring frost date in your region. This timing allows sufficient time for the plants to awaken and establish new growth before they are returned outside.
For bare-root plants, remove the dried foliage and soak the roots in lukewarm water for a few hours to rehydrate the tissues. After rehydration, pot the plants into fresh, well-draining potting mix. Check the stems for firm, green tissue, and prune any remaining soft or dead stems back to a healthy node. Potted plants that were stored semi-dormantly should also receive a light pruning to shape their growth and remove any winter-damaged tips.
Once potted, place the geraniums in a warm, brightly lit area and resume regular watering to encourage new root and shoot growth. As the threat of frost passes, the plants must be gradually acclimated to the outdoors, a process called “hardening off.” This involves exposing them to increasing periods of direct sunlight and outdoor temperatures over a one to two-week period before they are permanently placed back in the garden.