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While December might seem like the perfect time to stay wrapped up indoors, a surprising number of vegetables and flowers can still be nurtured under the cover of a greenhouse, to ensure your garden looks beautiful all year round.
What to plant in your greenhouse in December
Thinking about what to grow in December? Greenhouses and grow houses are the ideal starter locations for all sorts of seedlings and can keep winter blooms thriving through the darkest days. Here are our top recommendations for what to plant this month.
Growing vegetables in December
Garlic
Growing garlic is a bit like magic. Sowing a single clove and unearthing a whole bulb? It never gets old. December is the perfect time to plant garlic; sow it outdoors if you have free-draining ground or, if your soil is heavy, start cloves off in pots in the greenhouse or on a windowsill. While you can grow garlic bought from the supermarket, the results can be disappointing. Instead, aim to source bulbs from a garden retailer for a more promising return.
How to grow
Fill a module tray with compost and bury one clove per cell, with the pointed end up. Water them in and keep them in a greenhouse or sheltered cold frame.
Care tips
Keep the compost moist but not wet. In spring, plant your garlic outdoors 10-15cm apart. If young, curling flower stems - known as ‘scapes’ - appear, snip them off so the plant continues to put energy into the bulb. Take them into the kitchen instead of throwing them on the compost heap. They’re delicious sautéed in a pan and topped with a knob of butter.
When to harvest
Your garlic will be ready to harvest from June when the leaves start to yellow. Use a fork to lift them from the ground. Enjoy your crop straightaway or hang your garlic to dry in the sun, so the bulbs store for longer.
Broad beans
Easy to grow and highly productive; there’s a lot to love about broad beans. Sow them in December and you could savour a first crop as early as May.
How to grow
While you can sow some varieties of broad beans outdoors during a mild December, others will germinate better under cover. Fill a modular tray with compost and sow one bean per cell, before watering them in.
Care tips
Cover your seed trays to prevent mice from nibbling the beans before they emerge. Keep the compost moist and bed young plants outdoors in early spring, 15-20cm apart. It can help to harden them off for a week or two first, to prepare them for life outdoors. Water them into the ground and keep on top of the weeding. Tall cultivars might need plant supports or stakes to keep them upright as the heavy bean pods appear.
When to harvest
Harvest the pods when they are full and start to firm up. Open the jackets with your thumb and pop out the fresh beans to enjoy raw or cooked.
Herbs
Winter is a brilliant time to fill a heated greenhouse with fresh herbs, ready to enliven your cooking during the coldest, darkest months. Parsley, basil and chives will grow undercover if sown in pots in December. Parsley will be best left in a container as it can be a real thug if given free-range in the garden. Chives can be planted out in spring, to enjoy into the future.
How to grow
Fill plant trays with compost and water them before sowing seeds according to the individual instructions. Watering before sowing will help prevent the delicate seeds from being displaced.
Care tips
Keep your trays moist, but ventilate your greenhouse to avoid airborne fungal diseases and mould. Plant your herbs out or move them into garden pots when the air temperature warms up.
When to harvest
Harvest your herbs when the plants are well established and sprouting fresh leaves.
Flowers to grow in December
Snapdragons
Antirrhinums - known more commonly as ‘snapdragons’ - are classic cottage garden annuals. Loved by bees and other wildlife, they come in a rainbow of cheery colours. Choose your favourite and sow the seeds in a heated greenhouse in winter to enjoy a burst of bright colour come summer.
How to grow
Fill a tray with compost, water the surface and sow seeds thinly on the top. Put them in a heated propagator or cover them with a clear plastic bag.
Care tips
Once your seedlings have established, transfer them to larger pots and grow them on in a warm spot. Before planting them in the garden (after all risk of frost has passed), take a week or two to harden them off during the daytime, to get them used to outdoor temperatures.
When to harvest
Your snapdragons should be in flower and ready to enjoy from June onwards.
Cyclamen
For a pop of colour during the dark days of winter, introduce pots of shop-bought cyclamen to your greenhouse. Late autumn is the best time to bring these delicate beauties home for seasonal displays, but you may still get away with it in early December. If you nurture your flowers in an unheated greenhouse and frost is forecast, bring them indoors and find a warm windowsill or spot in the conservatory to keep them looking their best.
Care tips
Ensure your greenhouse is kept at 10 degrees or above in winter (or bring your flowers indoors) and water minimally when your cyclamen’s compost is dry; overwatering them can be fatal!
Rhino Greenhouse tips: Garden jobs for December
As the year comes to an end, use time in the garden to carry out a few jobs in and around your greenhouse:
- Check your greenhouse plants and water (sparingly!). Through winter it’s important to keep the air inside as dry as possible to prevent frost damage.
- If you haven’t already, insulate your greenhouse to keep the heat in and the frost out.
- Move any last tender plants from your garden under cover, to help them see out the season.
- Remove snow from your greenhouse and cold frames if inclement weather arrives.
