While winter is the quietest time in the greenhouse in terms of active plant growth, there is still plenty to do as the temperature falls and the days draw in. With spring only three months away, now is the time to make sure that tender plants are adequately protected from the cold frosts to come and that the last cuttings and sowings of autumn are looked after until the time comes for them to be planted out.
Managing the Winter Greenhouse
One of the first jobs to prepare for winter is to clean off all the shading, if you have not already done so and make sure that the greenhouse glass is kept clean to let in as much light as possible, the plants needing all they can get at this time of the year.
As winter begins to bite in December – the darkest month – plant growth slows accordingly and a little patience is called for until the days slowly begin to lengthen again. In the run-up to winter, greenhouse heaters need to be checked to make sure that they are working efficiently and insulating the greenhouse with bubble-wrap can be a relatively inexpensive way to help keep things warm and reduce heating bills. As a result, it need not cost a great deal to be able to keep things ticking over in the winter greenhouse – a night-time temperature of around 7 degrees C, for example, will enable perpetual-flowering carnations to provide a floral display throughout the year.
Ventilation remains as important as ever and on sunny winter days, the greenhouse can be ventilated freely, though it is important to watch out for cold breezes which can quickly chill things down and remember to shut the vents before the temperature falls in the late afternoon. The greenhouse will need to be kept shut, however, on windy or foggy days and if either persists for any length of time, the plants may need additional insulation to keep them safe. Winter watering should be done sparingly, only when the soil shows signs of drying out – but before it starts to shrink away from the pot sides – and as early in the day as possible, to give foliage the chance to dry off thoroughly before night-time. Over-watering needs to be avoided, since it can sometimes lead to root problems, especially in young plants, so it is better to keep them slightly on the dry side and in good light.
Any outstanding potting up needs to be completed at the very beginning of winter, including annuals sown in September and cuttings of fuchsias and pelargoniums; if all goes well, many of these should be ready to be potted on in the spring. Many varieties of hardy plants can be “forced” – encouraged to flower early – if they are lifted from the garden and potted up in early winter. Candidates include the likes of polyanthus, aquilegia and Christmas rose, which should be taken indoors once the flowers begin to show.
A wide range of bulbs can also be brought on in this way to provide a display at Christmas, including daffodils – which will need to have been artificially cooled first – hyacinths and narcissi such as Grand Soleil d’Or or Paper White.
Towards the end of January or early February, many types of greenhouse and garden plants can be sown, including begonias, gloxinias, followed later in February by the likes of freesias, coleus and primulas. Early cropping vegetables can also be sown and as the greenhouse temperature rises towards the end of the month, it will soon be time to think about preparing to sow tomatoes too.
The winter greenhouse is also a refuge from the frost for a number of summer flowering plants, such as begonias, hydrangeas and some kinds of fuchsias, which safely sit under the staging until March. Although they are dormant, they will still need occasional checking to make sure that their compost does not dry out completely. In the same way, any summer-flowering tubers or bulbs which have been lifted for over-wintering in the greenhouse need to be examined periodically for any signs of fungus or rot – and any affected ones discarded and destroyed. Although generally pests are much less active at this time of year, it is still a good idea to keep a look out for the likes of whitefly early in the season and vine weevil throughout the winter.
It can sometimes be difficult to remember, in the grey and gloom of a typical British winter, as the morning sun struggles to raise its head briefly above the horizon before slipping back into night, that spring really is only just around the corner. However, between all the potting up early in the winter, the sowing later on and the prospect of forced flowers for Christmas, the greenhouse owner is never without a reminder for long.