How to Overwinter Plants
How to Overwinter Plants
Overwintering is the term that refers to the process of helping tender plants through the harshness of the cold season. In gardening terms, the winter period is often punctuated by the first and last frosts. This means that the parameters are set by your location in the country - the south will benefit from a few extra weeks frost free, whereas the further north you travel the quicker the frosts are likely to appear and the later they are likely to leave. The calendar months of winter are thought of as November, December and January – this does only provide an approximation and it is wise to get to know your garden and how the frosts impact upon it wherever you are in the UK.
Indoors or Out?
Different plants will react to overwintering differently; some semi-tender herbs like parsley and chives can be brought inside for the winter and can be treated in the same way as a house plant. As long they get enough light they will continue to grow – albeit slightly slower on a windowsill. Similarly, the majority of citrus plants will need protection from the earliest threat of frost. A conservatory is the ideal place if you are lucky enough to have one, although a frost-free greenhouse or a part of your home that enjoy good light is adequate. Remember not to place them too close to a window or radiator so that they do not scorch. The key is to maintain a constant temperature as much as possible so cold drafts and dry heat will not be good for the plants.
There are many plants which benefit from some winter protection without needing masses of work to ensure their survival. Olive trees and some agapanthus varieties will struggle in the very depths of winter so moving their pots to against a house wall, grouping them together and covering them with a sheet of horticultural fleece will considerably increase their chances of making it through the cold weather relatively unscathed.
The Benefits of a Greenhouse
If you have a greenhouse at your disposal then overwintering your favourite plants becomes a lot easier. A whole host of tender beddings plants can be brought into the greenhouse for the winter, either in their pots or lifted out of the borders into temporary containers. Pelargoniums and impatiens, for example, will cope with the winter in the greenhouse potted up and sparsely watered. This is often a good way to overwinter plants as often it only needs to be warm enough to keep the frost at bay so a glass greenhouse will do the job as there is usually enough light provided to keep things ticking over. If your greenhouse is not heated, then it is a good idea to insulate the greenhouse over the winter. The easiest way to do this is to simply stick bubble wrap to all the glass panes with sticky tape or proprietary pegs. As heat rises then this is best done to the roof of the greenhouse as well as the sides, although if you can only reach the sides this will be beneficial and keep you safe at the same time!
Bulbs and Corms
Other plants will be overwintered through storing their tubers, bulbs or corms. Cannas and Dahlias should be lifted at the first frost and all the foliage removed ready for overwintering. The tubers or bulbs should then be cleaned of soil and inspected for any pest or diseases. Once you are satisfied that they are healthy enough for storing, leave them to dry out on the surface before storing in a cool, dark and dry place. A garage or shed is ideal. It is possible - in milder areas – to leave these plants in situ outside as long a thick mulch is applied – this obviously carries a degree of risk with it as no-one can predict the weather precisely enough to forewarn us regarding the forthcoming season.
When it comes to mulching for any purpose; either for the soil structure or for overwintering the same rule applies – the mulch needs to be a decent depth (at least a 5-10cm) in order to be of benefit. Bark chippings, compost (even old, spent compost from last year’s pots will be fine), or topsoil are all accessible and affordable mulch types. Think of mulch as a winter duvet to provide some worth for your favourite perennials!
If you are determined to see your plants through the winter, then overwintering indoors is undoubtedly giving them the best chance of survival - it might be worthwhile to also take cuttings of your beloved plants as extra insurance. In the worst scenario, you will still have something to plant back out in the garden come the springtime and best scenario you will have more, new and healthy plants - which is what we love!
Fruit and Vegetables
If you grow fruit and vegetables, then there are also a few edibles which can be overwintered in the greenhouse. For example, chillies and pepper plants can be overwintered in the same way as tender florae in the greenhouse - by keeping them frost free, with just enough water to not dry out.
The X Factor
The process of overwintering depends on a several factors. The plant species itself is probably the most important. Then the resources available to you for overwintering such as a heated greenhouse, unheated greenhouse or other inside space such as a garage or conservatory. The third factor is plain old luck! Sometimes all the steps can be followed to the letter, and you may have had success previous years then, despite no difference, the plant may not make it out of winter for inexplicable reasons. This is why cuttings are handy, as is a list of the much-loved species and variety for frost tender plants so that you can, when all else fails, come to us for replacements.