The common garden geranium, a tender perennial botanically known as Pelargonium, is typically cultivated as an annual in regions experiencing cold winters. These plants cannot survive freezing temperatures, as they originate from the warmer climate of South Africa. To preserve favorite varieties and ensure a blooming display the following spring, gardeners must employ specific care methods to protect the plant during the winter months. This process involves either maintaining the plant in an actively growing state indoors or inducing a state of semi-dormancy in a cool, dark location.
Preparing Geraniums for Winter
The transition to winter care begins before the first hard frost arrives, as even a light freeze can cause significant damage. For plants growing in the garden bed, they must be carefully dug up, ensuring as much of the root ball remains intact as possible. If the plants are already in containers, they should be moved to a sheltered area to begin the preparation process.
Pruning is necessary to reduce the plant’s size and minimize stress before moving it to its final winter location. Cut back the stems by about one-third to one-half of their total length, which concentrates the plant’s energy. This reduction in foliage also helps the plant manage with lower light levels indoors or conserve energy during storage.
Thorough cleaning is necessary before bringing plants inside to prevent pests and diseases. Remove all dead leaves, spent flowers, and loose debris from the soil surface and the plant structure. Closely inspect the undersides of leaves and stem joints for common pests like aphids, whiteflies, or spider mites. Applying a preventative insecticidal soap spray or neem oil treatment eliminates lingering hitchhikers that could proliferate indoors.
Overwintering as an Indoor Houseplant
One effective method is to keep the geranium actively growing indoors, treating it like a typical houseplant throughout the winter season. The plants require a location that provides high light intensity, such as a sunny south-facing window, to compensate for the short days. If natural light is limited, supplemental grow lights should be utilized to maintain adequate photosynthesis.
The ideal indoor temperature for active growth is cool, preferably ranging from 60 to 65 degrees Fahrenheit. Placing the plant away from heat vents, fireplaces, or other hot drafts is important, as excessive heat combined with low light can result in weak, spindly growth. Cooler temperatures allow the plant to slow its metabolism without entering true dormancy, preventing it from becoming “leggy.”
Watering must be significantly reduced compared to the summer months to prevent root rot. Only water the plant when the top inch of soil feels dry, ensuring the pot drains completely. Fertilizer application should be suspended entirely during the winter, as the plant’s growth rate is naturally slowed due to reduced daylight hours. If the plant exhibits overly long or weak stems, a slight pinch back just above a leaf node will encourage bushier growth.
Storing Geraniums in Dormancy
A space-saving alternative to active growth is to induce a period of semi-dormancy, which requires a cool, dark, and dry storage environment. The temperature in the storage area, such as a garage or unheated basement, must be maintained consistently between 40 and 50 degrees Fahrenheit. This temperature range is low enough to slow the plant’s metabolism significantly but high enough to prevent freezing, which would be lethal.
Bare-root storage is highly space-efficient. The plant is dug up and the soil is gently shaken off the roots. After a brief pruning, the plants can be placed in a paper bag, a cardboard box, or hung upside down. Hanging the plant upside down allows remaining moisture to flow toward the crown, helping to preserve the root structure.
Potted plants can also be stored dormant by allowing the soil to dry out completely before moving them into the cool, dark location. Regardless of the method, the plants should be checked monthly throughout the winter for signs of desiccation or mold growth. Dormant bare-root plants may need a brief soak of their roots in water for an hour if the stems appear shriveled or excessively dry. The goal is to provide just enough moisture to keep the crown alive without encouraging active growth, which would quickly fail in the dark.
Transitioning Back to the Outdoors in Spring
Waking up dormant geraniums and preparing all overwintered plants for the outdoor growing season requires a gradual process. Approximately six to eight weeks before the final expected frost, dormant plants should be removed from storage and aggressively pruned back to firm, green stem tissue. Bare-root plants benefit from a two-hour soak in room-temperature water to rehydrate the roots before being potted into fresh, well-draining soil.
All overwintered geraniums should be repotted, refreshing the old soil with a new potting mix to provide renewed nutrients. Place the newly potted or repotted plants in a bright, sunny window or under supplemental light to initiate new growth. As new leaves appear, a diluted, balanced liquid fertilizer can be introduced to support the emerging growth.
The final step before placing the plants in their permanent summer location is the hardening-off process, which acclimatizes them to outdoor conditions. Start by placing the geraniums in a sheltered, shaded spot outdoors for a few hours each day, gradually increasing their exposure to direct sunlight and wind over a period of one to two weeks. The plants should only be left outdoors overnight once the risk of frost has completely passed and nighttime temperatures are consistently above 50 degrees Fahrenheit.