How to make the most of your winter greenhouse
Greenhouses ain’t what they used to be. Nowadays they’re as likely to double up as a home office or yoga studio: and as gardens shrink, the traditional six-by-eight is yielding ground to mini greenhouses small enough to slot onto a balcony. Ikea’s tiny cabinet greenhouse is just 18in wide – small enough to perch on a windowsill.
But whether you like your greenhouses traditional or new wave, they really start to earn their place in the garden at this time of year. Greenhouses hog our attention in summer but, in fact, they’re at their best now, offering warmth, shelter and a place to carry on gardening without having to get cold and wet. Get planting now and your winter greenhouse becomes a little sanctuary of colour, scent and flavour: you’ll almost be sorry when spring comes around again.
Six things to do in a traditional winter greenhouse
1. Force spring bulbs
Head gardener Tom Brown, who looks after the 12 Victorian glasshouses at West Dean, Sussex, knows all about keeping greenhouses looking good in winter. This year he’s filling his staging with super-early forced spring bulbs.
“When you grow bulbs in pots you get them up to eye level,” he says. “In winter, when there’s so little colour around, you pick up on their beauty even more.”
You can indulge in the daintiest spring bulbs under glass, safe from the hurly-burly of the open garden. Tom likes miniature tazetta Narcissus ‘Avalanche’, hyacinths such as dark maroon ‘Woodstock’, early-flowering species tulips like Tulipa humilis and crocuses (Crocus chrysanthus ‘Snow Bunting’ is scented). In a greenhouse, they flower weeks sooner than outside.
Plant into reclaimed terracotta pots now, give them a soak to settle them in, then don’t water again till they produce shoots. After that, water a little more and feed with liquid seaweed every few weeks. Once they’re over, pop the pots in an out-of-the-way corner and do it all again next year.
2. Hang on to summer
Summer bedding pelargoniums don’t know when to stop: give them the slightest encouragement and a middlingly warm greenhouse and they’ll often just keep flowering.
Scented-leaf pelargoniums and old Victorian “unique” varieties are particularly good for winter flowers. Pot up into generous containers and bring under cover, but instead of drying them off to overwinter, keep watering (a little more sparingly) with the occasional dose of high-potassium tomato feed for summery flowers till spring.
3. Get the veg garden started
Greenhouses are seed-sowing powerhouses, but don’t wait till spring: get ahead and sow hardy broad bean ‘Aquadulce Claudia’, Japanese onions and garlic into saved loo roll inners and newspaper modules now. Move into a cooler cold frame for winter, then plant out in February as robust seedlings with a month’s head start.
4. Visit the tropics…
Turn up the heat and you can transform your greenhouse into a paradise filled with exotic blooms. In the heated greenhouses at West Dean, where the temperature never drops below a balmy 10-15C, Tom goes to town in winter with jungles of waxy anthuriums, flouncy clivias and hippeastrums (amaryllis).
But if you’re not keen on remortgaging the house to pay the heating bills, fake it. Start with generous potfuls of ravishingly beautiful Nerine sarniensis (aka the Jersey lily) – often still flowering in December – and elegant Amaryllis belladonna (common name, the Guernsey lily). With gentle warmth, around 5-8C, Tom says large-flowered Cyclamen persicum, streptocarpus (cape primrose) and even cymbidium orchids flower right through winter.
“Exotic plants relish the bright, dry environment in a greenhouse,” he says.
5. Grow a winter salad bowl
Why not free yourself from the tyranny of bagged supermarket salads this winter by packing your greenhouse with greenery? Hardy lettuces such as ‘Black Seeded Simpson’, oriental mizuna, herby chervil, spicy American land cress and crisp Claytonia perfoliata all thrive in cool greenhouse borders through winter.
It’s too late to sow seed, so stock up on ready-grown plug plants (rocketgardens.co.uk): plant straight away, 6in apart, and they’ll be pickable from November.
6. Stash your dahlias
In southerly bits of the country you can risk leaving frost-tender tubers like dahlias, cannas and yacón outside, tucked beneath a blanketing mulch of autumn leaves. But if you garden where frost bites deep, carefully dig them up to bring indoors for winter. Dry, frost-free greenhouses make invaluable dahlia storage sheds.
Cut back foliage, brush off any soil, tie a label round the neck and dry upside-down for a fortnight. Then pack into crates, cover with spent compost and stash under the greenhouse staging till spring.
Six things to do in a tiny greenhouse
1. Make a Christmas terrarium
London-based designer Isabelle Palmer specialises in packing plants into the tiniest of spaces – and she loves using micro greenhouses as ersatz terrariums. She picks up cheap-as-chips starter plants from garden centres, majoring on Christmassy evergreens like dwarf conifers, ivy and wiry Muehlenbeckia complexa, plus winter-flowering violas. Then she gets creative.
Start with a layer of gravel in a deep tray the same size as the base of the greenhouse. Top with peat-free compost, then plant your miniature forest. Water in, then add moss, pieces of wood, pebbles, pinecones, or even little figurines to conjure up a Christmassy scene.
“Making these mini worlds is such a pretty thing to do,” says Isabelle. “And they don’t have to stay on the windowsill – you can move them onto your table for a dinner party, too.”
2. Plant a winter herb garden
Dig up mint, marjoram, French tarragon and chives to pot up and bring into the shelter of a balcony greenhouse and they’ll stay green weeks after those out in the open have shrunk back in the cold.
Germinate a sprinkle of coriander, chervil, parsley or Greek basil seeds sown direct into pots in a windowsill growhouse and they should be snippable by early spring, too.
3. Start a microgreens farm
You can grow your own winter salad even on balconies and windowsills: mini greenhouses take tray after tray of microgreens, sown every few weeks for a stream of nutrient-packed seedling veg to add to sandwiches, salads and stir-fries. Isabelle Palmer’s favourites are brilliant burgundy ‘Bull’s Blood’ beetroot, spicy radish and green kale.
“It’s the perfect way to use a little greenhouse with shelves,” she says. “I couldn’t believe how quick and easy it was.”
Most vegetables make good microgreens: try rocket, basil, chard, calabrese and even sunflowers for punchy flavours. Just avoid parsnips (they’re poisonous as seedlings) and buy organic to avoid artificial seed treatments.
Half fill shallow trays (takeaway trays work well) with peat-free compost and sow thickly on top. Cover with more compost, water, pop into the greenhouse and that really is it. Within as few as 10 days your little forest of greenery will be roughly 2in tall and ready to snip.
4. A balcony alpine house
You only really appreciate teeny-tiny alpine plants when you’re nose to nose with their dainty flowers and filigree foliage: not always practical (or easy on the knees) when they’re growing in the ground, but a delight when they’re at eye level in balcony greenhouses.
Mini alpine houses aren’t just for summer, though. Many alpines look good year round: weave a tapestry of colour from smoky-purple sempervivums threaded with delicate evergreen ferns such as Blechnum penna-marina or Adiantum aleuticum, just 2in tall and evergreen when sheltered. Then add a spangling of miniature winter flowers. In the cool shelter under glass, autumn stars like gentians (Gentiana sino-ornata) flower into late autumn.
Silvery-leaved Moroccan daisy, Rhodanthemum hosmariense and diminutive Cyclamen coum bloom all winter, with elegant Iris reticulata and snowdrops for earliest spring.
Arrange choice specimens theatrically in matching ceramic containers or create mini gardens in shallow troughs of gritty compost.
5. Overwinter your chillies
Instead of ditching your chilli plants at season’s end, convert them into ersatz houseplants. Smaller-fruited chillies like ‘NuMex Twilight’ and ferociously hot bird’s eye chillies are easiest to coax through low light levels, especially tucked inside a cosy mini greenhouse indoors.
Keep them on the dry side and don’t worry if they drop their leaves – they’re just hibernating. Once they stir again in spring, water and feed normally and they’ll bounce back to burn your mouth off for another year.
6. Create more houseplants
Greenhouses really earn their keep when you use them to make new plants for free. New houseplants can set you back the price of a round in the pub these days – so keep your cash in your pocket and use your mini greenhouse to take cuttings instead. Double down on your own favourites, or raid friends’ collections (the offer of a new plant in return usually does the trick).
All you need is a growing shoot snipped off just below a leaf joint to create new cheeseplants (Monstera deliciosa), rubber plants (Ficus elastica) and philodendrons.
A single leaf, picked with stalk attached, will give you baby African violets (Saintpaulia) or peperomias.
Sink into pots of gritty compost, water, then pop into your mini greenhouse to root.
Six of the best mini greenhouses
Esschert design greenhouse. This stylish offering has a carrying handle for use outside or to display your houseplants indoors. £59.99 (robertdyas.co.uk)
Plantpak Grow House. This doesn’t take up much space but will keep plants well protected. £124.99 (marshallsgarden.com)
Wooden growhouse. A quick and easy to assemble solution to winter growing that holds up to eight seed trays and doesn’t take up much space. £119.99 (cover not included, £23.99) (crocus.co.uk)
Windowsill propagator. A windowsill is the perfect spot to start off seeds and keep herbs going all winter. The tray ensures plants are watered automatically for up to 14 days. £24.35 for 7 (amazon.co.uk)
Indoor greenhouse. The smart-looking Socker mini greenhouse will allow you to propagate more houseplants over winter. £12 (ikea.com)
Balcony greenhouse. The Juliana Balcony Greenhouse is an ingenious way of maximising a small outdoor space. £431 (twowests.co.uk)
How to heat your greenhouse
Even unheated greenhouses are warmer than outside by two or three degrees: add heating, though, and you can fend off frost altogether. Most heaters are heavy on fuel and the environment – so try these greener alternatives:
Insulation
The aim is to trap heat so none is wasted. Line glass with thick bubblewrap – or avoid plastic and line brick walls with thick cardboard, plus the roof whenever it’s really cold.
Passive solar
Water is incredibly efficient at absorbing the sun’s heat during the day, then releasing it at night. Stand black-painted drums of water in your greenhouse for natural night storage heaters powered by the sun.
Heat mats and propagators
Pay only for the heat you need: thermostatically controlled soil warming cables and propagators germinate winter-sown seedlings more quickly, while heat mats keep the chill off larger plants.
Hotboxes
If you can lay your hands on some fresh manure, you can heat your greenhouse the Victorian way. Dig a hole or build a raised box at least 9 sq in and fill with manure. In a week or so it’ll be steaming with heat and capable of warming your greenhouse for a couple of months.
The greenhouse retreat
If you have space, a few creature comforts turn a greenhouse into a cosy retreat where you can relax among the plants.
Curl up in a rattan rocking chair and add a cushion. A camping stove and kettle, plus a mini fridge, make your oasis complete.
If you must have contact with the outside world, take a waterproof radio with you.
