Greenhouse Growing in December
As temperatures drop and the garden slows down, your greenhouse becomes more valuable than ever. December may feel like a quiet month outdoors, but inside a greenhouse, there’s still plenty to grow, protect, and enjoy. From sparkling winter displays to fresh greens and festive propagation projects, your glasshouse can become a sanctuary – for plants and for you.
A greenhouse isn’t only for tomatoes and summer seedlings. Think of it as a trophy cabinet or even a giant terrarium, a miniature garden or ecosystem under glass. In winter, it can house treasured plants and collections you want to admire from inside and out. If you pass your greenhouse daily, why not make it beautiful? Terrarium inspiration also reminds us that miniature ferns, mosses, succulents, and cacti thrive in sheltered conditions. Your greenhouse can offer similar protection – just on a larger scale. Personally, I move my roses and Acers into the greenhouse in the winter. I have a number of roses in containers, which seem to sulk through winter frosts. They do far better in the greenhouse. Acers just seem to generally sulk anyway, but I try to keep them happy!
Light is precious in winter, so cleaning your greenhouse is essential. See our Preparing Your Greenhouse For Winter… guide. In short:
- Clean inside and out: Remove algae, fallen leaves, and debris from glass, gutters, and corners.
- Check structure: Replace damaged panes, repair seals, and ensure vents open smoothly.
- Tidy surfaces: Sweep floors and shelving, empty old pots, and add spent compost to borders or compost bins.
This is also the perfect moment to inspect for pests hiding in pots or framework, tiny slugs, snails, and vine weevil grubs love to overwinter in sheltered spots. Once clean, begin creating a display rather than simply “storing” plants.
Tender plants and borderline exotics should move under glass unless you live in a mild region. Where outdoor planting is too risky, use a biodegradable or recycled fleece layer to protect what must remain outside. If you need a seasonal display, hardy potted plants, chrysanthemums, cyclamen, violas, pansies, early bulbs, penstemons, salvias can brighten an unheated greenhouse beautifully. I have lots of salvias in the garden – more because they are really easy to take cuttings from, but also because the bees love them! I move them into the greenhouse from December – February then start hardening them off with the greenhouse door open during the day.
Keep heavy pots on the ground and smaller ones on benches. Use slates or wooden blocks beneath pots to improve airflow. Space plants apart to avoid leaves touching, this reduces risk of mould. Ensure regular ventilation, even on cold days, to prevent dampness.
A winter greenhouse can continue feeding you, even in December. Produce such as salad greens, herbs, pea shoots, parsley, winter cabbages, kale, winter lettuce, broad beans and garlic are easily grown and survive the colder temperatures. A greenhouse is generally about 5°C warmer than outside, giving seedlings a much-needed edge. Use bubblewrap insulation or a small heater to keep the greenhouse frost-free. Pre-heat the space if needed, especially for gardeners sensitive to cold. Set up a comfortable workstation with good access.
December in the greenhouse is a mix of care and creativity. With a clean structure, thoughtful plant protection, regular ventilation, and a touch of seasonal sowing, your greenhouse becomes a warm refuge, not just for plants but for you as well. As the days slowly lengthen, your efforts now will reward you with fresh growth, colour, and resilience in the months to come.
