Successfully overwintering regal pelargoniums is a crucial skill for any gardener wishing to enjoy these spectacular plants year after year, as they are tender perennials that will not survive freezing temperatures. Unlike simply bringing a plant indoors, proper overwintering is a deliberate process of encouraging dormancy, a state of rest that allows the plant to conserve energy and, critically, experience the cool period required for future flower bud formation. The process involves a significant reduction in water and a complete cessation of feeding, combined with providing a cool but bright environment. Mastering this period of rest is the key to ensuring not only survival but a vibrant and floriferous display the following spring.
The primary goal of overwintering is to provide the plant with a period of dormancy. In their native habitat, plants have natural cycles of growth and rest dictated by seasonal changes. For regal pelargoniums, this rest period is not just for survival; it is a prerequisite for blooming. The initiation of flower buds is triggered by a sustained period of cool temperatures, typically between 10-15 degrees Celsius. Without this cool dormancy, the plant may survive the winter, but it will likely produce lush foliage with very few, if any, of its characteristic large flowers come spring.
Preparation for overwintering should begin in the late summer or early autumn, well before the first frost is expected. The first step is to thoroughly inspect the plant for any pests or diseases. Bringing an infested or diseased plant indoors can lead to a widespread problem during the winter months when pests can multiply rapidly in a protected environment. Treat any issues you find while the plant is still outdoors. It is also beneficial to give the plant a „hard prune“ at this time, cutting the main stems back by about one-third to one-half. This reduces the overall size of the plant, making it easier to manage indoors, and removes any weak or leggy growth.
The transition from outdoors to indoors should be gradual if possible. A sudden change in light, temperature, and humidity can shock the plant. If you can, move the plant to a progressively shadier spot outdoors for a week or two before bringing it inside. Once indoors, you must choose the right location. The ideal spot for overwintering a regal pelargonium is a place that is both cool and bright. An unheated porch that stays above freezing, a cool conservatory, a bright garage, or even a cool spare room with a bright window are all excellent options.
Once the plant is in its overwintering location, your care routine must change dramatically. This is where many gardeners make the mistake of caring for the plant as they did during the summer. During dormancy, the plant’s metabolic processes slow to a crawl, and its need for water plummets. You should water only very sparingly, just enough to prevent the soil from becoming completely bone dry. This might mean watering as infrequently as once every three to six weeks. Overwatering during winter is the most common cause of failure, as the inactive roots will quickly rot in cold, damp soil. All fertilization must be stopped completely until new growth appears in the spring.
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The pruning preparation
Pruning is a critical preparatory step for successfully overwintering your regal pelargonium. The best time to perform this major prune is in the late summer or early autumn, after the main flowering season has concluded but before the plant is brought indoors. This timing allows the plant to heal from the cuts and begin to harden off before it enters dormancy. The primary purpose of this pruning is to reduce the plant’s size, remove old and unproductive wood, and encourage a strong framework for the following year’s growth. A well-pruned plant is more manageable indoors and is less likely to suffer from diseases due to improved air circulation.
Using a pair of clean, sharp secateurs or pruning shears, you should aim to cut back the main stems by approximately one-third to one-half of their length. Be bold in this process; while it may seem drastic, this „hard prune“ is essential for rejuvenating the plant. Make your cuts just above an outward-facing leaf node. This will encourage the new shoots that emerge in the spring to grow outwards, creating a more open and attractive shape rather than a tangle of inward-growing stems. Remove any weak, spindly, or crossing stems entirely, focusing on leaving a well-spaced framework of strong, healthy branches.
After pruning, it is also a good time to tidy up the plant at its base. Remove all remaining leaves from the pruned stems. This may look severe, leaving you with a collection of bare sticks, but it is a beneficial step. Removing the old foliage eliminates any potential hiding spots for pests like aphids or whiteflies and removes any leaves that may be carrying fungal spores. This clean, bare structure is less likely to suffer from fungal diseases like botrytis (grey mould) in the cool, potentially damp conditions of winter storage.
The final part of the preparation involves a thorough clean-up of the pot. Remove any fallen leaves or debris from the surface of the soil. This sanitation helps to reduce the overwintering sites for both pests and diseases. A clean plant in a clean pot is far more likely to successfully navigate the challenges of the dormant season. This comprehensive preparation—a hard prune, defoliation, and a thorough clean-up—sets the stage for a successful period of rest and a vigorous return to growth in the spring.
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Managing light and temperature
The environmental conditions you provide during winter are the determining factors in whether your regal pelargonium merely survives or truly thrives. The two most important variables to control are light and temperature. Unlike many plants that can be stored in complete darkness when dormant, regal pelargoniums must be kept in a location that receives bright, albeit indirect, light throughout the winter. They need this light to maintain a minimal level of photosynthesis and to stay healthy during their rest period. A bright, unheated windowsill in a spare room or a glassed-in porch are ideal locations.
Temperature is the other critical component of the overwintering equation. The goal is to keep the plant cool, but consistently above freezing. The ideal temperature range for inducing dormancy and promoting future flower bud formation is between 10 and 15 degrees Celsius. This coolness is the signal to the plant to remain in a state of rest. Avoid placing the plant in a centrally heated room, as the warmth will prevent it from going fully dormant and may encourage it to produce weak, leggy growth that is highly susceptible to pests. Consistently cool temperatures are the key.
You must protect the plant from freezing temperatures at all costs. A single hard frost can be fatal to a regal pelargonium. If you are keeping your plant in a location like a garage or a porch where temperatures might dip close to freezing on particularly cold nights, be prepared to provide some temporary protection. This could be as simple as covering the plant with a layer of horticultural fleece or an old blanket overnight, or moving it to a slightly warmer, frost-free location temporarily until the cold snap has passed.
Throughout the winter, continue to monitor the conditions. You may notice that the plant sheds some of its remaining leaves, which is perfectly normal during dormancy. However, if the stems start to shrivel or the plant looks excessively desiccated, you may need to provide a small amount of water. The balance is delicate; you want to maintain a cool, bright environment with minimal water to encourage rest without allowing the plant to die of dehydration. This careful management of light and temperature is the essence of successful overwintering.
Waking the plant in spring
As the days begin to lengthen and the intensity of the light increases in late winter and early spring, your regal pelargonium will begin to show signs of waking from its dormancy. You may notice small new leaves or shoots starting to emerge from the nodes on the bare stems. This is the signal that the dormant period is coming to an end and that it is time to gradually adjust your care routine to support this new phase of growth. The timing of this awakening can vary depending on your specific conditions, but it typically occurs from late February to March.
The first step in waking up your plant is to increase the watering frequency. Begin by watering the plant thoroughly, allowing the excess to drain away. From this point on, return to the practice of checking the soil regularly and watering whenever the top few centimeters feel dry. The plant’s water needs will increase steadily as its new growth accelerates. This is also the time to move the plant to a slightly warmer location if it has been in a very cool spot, although it will still appreciate a location that is bright and protected from the intense, direct sun.
Once the plant is showing clear signs of active, vigorous new growth, you can begin to reintroduce fertilizer. Start with a balanced liquid fertilizer diluted to half-strength. Applying a full-strength fertilizer to a plant just emerging from dormancy can be too harsh for the newly active roots. Feed with this half-strength solution for the first two or three applications, spaced about two weeks apart. As the foliage fills out and the plant’s growth becomes more robust, you can then transition to a full-strength feeding regimen to power its development towards the flowering season.
This period of awakening is also the time for a final shaping and clean-up. You can perform a light „pinch prune“ on the new shoots to encourage branching and a fuller, bushier plant. Simply pinch off the growing tips of the new stems. This will stimulate the growth of side shoots, resulting in a more compact plant with more flowering stems. Remove any small, weak shoots that are growing in the center of the plant to maintain good air circulation. This final touch puts the plant on the right path for a spectacular display of blooms in the months to come.
