Why Overwinter Pelargoniums?
Overwintering pelargoniums in the UK is a popular practice among gardeners keen to preserve these vibrant flowering plants through the colder months. While many pelargonium varieties are tender and susceptible to frost damage, adopting specific overwintering strategies allows them to survive and thrive for years. This practice not only saves you the cost of replacing plants annually but also ensures you retain specimens with desirable flower colours, forms, and growth habits.
- Preserves valuable plant specimens.
- Saves money on annual replanting.
- Ensures continuity of favourite varieties.
- Allows for propagation in spring.
The primary motivation is plant survival. Pelargoniums, often mistakenly called geraniums (though true geraniums are hardy perennials), are typically grown as annuals in much of the UK due to their intolerance to freezing temperatures. However, by bringing them indoors or providing adequate protection, you can extend their lifespan significantly. This is particularly important for 'show' plants, those with sentimental value, or specimens propagated from cuttings of parent plants that are no longer available.
Beyond mere survival, overwintering enables plants to establish a stronger root system and more robust structure. A well-rested plant often produces more prolific blooms and healthier foliage in the subsequent growing season. It's a way to nurture your garden collection, preparing it for a spectacular display year after year.
Move plants indoors before the first hard frost, ideally when temperatures consistently drop below 10°C.
Understanding Pelargonium Hardiness
It's crucial to distinguish between the common zonal, ivy-leaf, and regal pelargoniums most people grow and the hardy geraniums (true Geranium species). While the common names can cause confusion, pelargoniums generally require winter protection in the UK. Some less common species or specific cultivars might exhibit slightly more resilience, but relying on this without confirmed hardiness is risky. For the vast majority of garden pelargoniums, winter is their biggest challenge.
The decision to overwinter depends on your gardening goals, the space you have available, and the types of pelargoniums you grow. If you treat them as disposable annuals, replacing them each year with new stock, then overwintering isn't necessary. However, for those who cherish their existing plants or wish to cultivate a more mature collection, it’s an essential horticultural skill.
Methods for Overwintering Pelargoniums
How do you successfully overwinter pelargoniums in the UK? Several effective methods cater to different circumstances, from bringing whole plants indoors to storing them dormant. Each approach requires attention to light, temperature, and watering to ensure the plant’s health during its rest period.
Method 1: Bringing Plants Indoors (Cool, Bright Storage)
This is perhaps the most common and effective method for garden pelargoniums. In late autumn, before the first frost, carefully dig up your pelargoniums. Gently remove as much soil as possible from the roots, or prune them back by about a third to a half to make them more manageable. Pot them into clean pots using a well-draining compost, or place them directly into trays. Water sparingly, only when the compost starts to feel dry. The key is to provide a cool (around 5-10°C), bright location. An unheated greenhouse, a bright porch, or a cool windowsill in a conservatory are ideal. Avoid direct heating, as this can encourage weak, leggy growth. Inspect regularly for pests like aphids or whitefly, which can thrive in indoor conditions.
Method 2: Dormant Storage (Root or Stem Cuttings)
For those with limited space, a more drastic approach involves encouraging dormancy. Plants can be completely dried off and stored upside down in a cool, dark place, or their roots can be stored similarly. Alternatively, you can take cuttings in late summer or early autumn. These cuttings are then treated as young plants and overwintered in pots in a frost-free environment, such as a greenhouse or cold frame, with minimal watering. This method is excellent for propagating new stock and saving space, but it requires the initial step of taking and rooting cuttings, which is akin to starting plants from scratch.
Pruning is vital before storage. For plants being brought indoors, cut back stems to encourage bushier growth and reduce the plant's size. For root storage, trim any straggly roots. The goal is to minimise energy expenditure and prevent disease.
Method 3: Overwintering in Situ (Hardy Varieties Only)
While most pelargoniums are not frost-hardy, some specific types, particularly certain species pelargoniums or hybrids that have been bred for greater resilience, may survive outdoors in milder parts of the UK if given significant protection. This usually involves cutting them back hard and covering the base with a thick mulch of straw, bracken, or horticultural fleece. However, this method carries the highest risk of loss, and for general garden pelargoniums, it is not recommended. Always confirm the hardiness of your specific variety before attempting this.
When repotting overwintered plants in spring, use fresh, free-draining compost and consider adding a little grit for improved drainage.
Assessing Plant Condition
During the overwintering period, minimal watering is key. Overwatering is the most common cause of rot and subsequent plant death. Check the soil moisture by touch; only water when the top inch or so feels dry. If plants are stored in a cool, dark place without much light, even less water will be needed. Some leaf drop is natural, but if you see stems turning black or mushy, increase ventilation and reduce watering immediately.
Reviving and Propagating Pelargoniums in Spring
What happens after the cold months? Successfully bringing pelargoniums through winter sets the stage for a spectacular summer display, but the transition requires careful management.
Assessing and Pruning
As daylight hours lengthen and temperatures begin to rise in early spring, it's time to assess your overwintered pelargoniums. Inspect them for any signs of disease or pest infestation. Prune back any dead, damaged, or leggy growth. Cut back stems to encourage branching and a more compact, bushy plant. Aim to shape the plant and remove any weak or spindly stems. This pruning stimulates new growth and prepares the plant for the upcoming growing season.
Repotting and Feeding
Once pruned, if the plants have outgrown their pots or if the compost is exhausted, it’s time to repot. Use a good quality, free-draining potting compost, perhaps with added perlite or grit for enhanced drainage. Water them in after repotting. Begin feeding your pelargoniums with a balanced liquid fertiliser once you see consistent new growth. Start with a weaker solution and gradually increase to the recommended strength as the plants establish themselves.
Taking Cuttings for New Plants
Spring is also the prime time for propagation. Healthy, established overwintered plants will readily produce new shoots suitable for taking cuttings. Using a clean, sharp knife or secateurs, take 10-15 cm stem cuttings from new growth. Remove the lower leaves and insert the cuttings into pots of well-draining compost or a mix of compost and grit. Keep them in a warm, bright place, misting them regularly and covering pots with a plastic bag or propagator lid to maintain humidity. Roots typically form within three to six weeks, after which they can be potted on individually.
This process not only allows you to create new plants for free but also helps to rejuvenate your stock, as cuttings often produce more vigorous plants than older, overwintered specimens. It's a core part of managing a pelargonium collection through the years.
The sustained effort of overwintering and propagating ensures continuity of prized plant genetics.
Gradual Acclimatisation
Before planting pelargoniums outdoors, it is crucial to acclimatise them gradually to outdoor conditions. This process, known as hardening off, prevents shock. Over a period of 7-10 days, move the plants outside during the day, returning them to a sheltered spot (like a porch or greenhouse) at night. Gradually increase their exposure to direct sunlight and wind. Only plant them out permanently once all risk of frost has passed and the weather is consistently warm.
When taking cuttings, ensure the stem is firm but not woody, making a clean cut just below a leaf node.
Companion Planting Considerations
As you prepare your garden for summer displays, consider companion planting to enhance your pelargoniums' health and visual appeal. While pelargoniums are not overly fussy, pairing them with plants that have similar watering and light needs can simplify garden management. For instance, growing them alongside plants like petunias or marigolds, which also appreciate good drainage and sun, can create a cohesive border. While companion planting isn't critical for pelargonium survival, it can contribute to a healthier garden ecosystem. For example, ensuring good air circulation around plants like begonias can help prevent fungal issues, a principle that also benefits pelargoniums.
Troubleshooting Common Issues
What problems might you encounter when overwintering pelargoniums in the UK, and how can they be addressed?
Leggy Growth
If your pelargoniums become leggy and stretched during overwintering, it's usually a sign they are not receiving enough light or are being kept too warm. Try to move them to a brighter, cooler location. Regular pruning in spring will help to create a more compact plant, even if they do stretch a little during storage.
Yellowing Leaves
Yellowing leaves can be caused by several factors. Overwatering is a common culprit, leading to root rot. Underwatering can also cause leaves to yellow and drop. Ensure you are watering correctly – only when the compost is dry. Nutrient deficiency can also cause yellowing, especially if the plant has been in the same compost for a long time. A mild liquid feed in spring, once new growth appears, will help.
Pest Infestations
Indoor environments, especially greenhouses, can be havens for pests like aphids, red spider mites, and whitefly. Inspect your plants regularly. If an infestation is found, try to deal with it promptly. Small infestations can often be removed by hand or wiped off with a damp cloth. For more severe cases, consider using insecticidal soap or a specific pest control product suitable for indoor plants. Good air circulation can help prevent some pest issues.
Fungal Diseases
Fungal diseases, such as grey mould (Botrytis), can develop in cool, damp, and poorly ventilated conditions. Ensure your overwintering area is well-ventilated and avoid letting leaves sit in water. Remove any dead or decaying plant material promptly, as this can harbour fungal spores. If grey mould appears, improve air circulation and remove affected parts of the plant. Ensure plants are not overcrowded.
Careful monitoring is paramount throughout the overwintering period. Early detection of problems allows for a swifter, more effective response, significantly increasing your chances of saving your beloved pelargoniums for the next season.
Maintain consistent, cool temperatures if possible; significant fluctuations can stress the plants.
When to Give Up
Sometimes, despite best efforts, a plant may be beyond saving. If the main stem has turned black and mushy, or if the root system is completely rotten, it's unlikely to recover. In such cases, it’s better to dispose of the plant to prevent potential disease spread to other overwintering specimens and focus your attention on healthier plants or new cuttings.