Even though active plant development is at its lowest during the winter in the greenhouse, there is still a ton to accomplish as the days become shorter and the temperature drops. The last cuttings and sowings from the previous autumn should be cared for until they are ready to be planted out during the winter months to ensure that they are suitably sheltered from the impending cold frosts.
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.
Plant development slows down as winter sets in in December, the darkest month of the year, and some patience is needed until the days start to gradually lengthen again. Verify the efficiency of your heaters or heating systems. Another reasonably cheap option to keep things warm and lower heating costs is to insulate the greenhouse with bubble-wrap.
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 into the evening. On windy or foggy days, the greenhouse must be kept closed, and if either condition lasts for an extended period of time, the plants may require additional insulation to keep them safe. Winter watering should be done sparingly, as early in the day as possible to allow foliage the best opportunity of drying out completely before nightfall, and only when the soil begins to show indications of drying out but before it begins to shrink away from the pot sides. Avoid over-watering as it can sometimes result in root issues, especially in young plants. Instead, keep them just a little bit dry and in adequate light.
Plant Care
Annuals seeded in September, and any other plants still in need of potting up need to be finished as soon as winter arrives; if all goes well, many of them should be prepared for transplanting in the spring. If hardy plants are removed from the garden and potted up in the early winter, they might be able to flower early, and get a headstart.
Towards the end of January or early February, many types of greenhouse and garden plants can be sown, including begonias and 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. Soon, it’ll be time to start thinking about tomatoes.
Many summer flowering plants, like begonias, hydrangeas, and some varieties of fuchsias, find refuge from the frost in the winter greenhouse where they can remain until March. Even though they are dormant, they will need to be checked from time to time to make sure that their compost doesn't totally dry out. Similar to this, any summer-flowering tubers or bulbs that have been pulled for overwintering in the greenhouse need to be checked for any symptoms of fungus or rot on a regular basis; any infected ones need to be removed.
