Contrary to popular belief the gardening year begins not in spring, when most weeds wake up, but in winter, with planning, seed buying, and those exciting first sowings.
While a cold frame is sufficient to protect seedlings from the ravages of the weather, a greenhouse or polytunnel makes sowing and tending the growing seedlings much more comfortable. No more sore back from crouching over a cold frame! And even a small greenhouse can be put to good use every single month of the year.
Using a Greenhouse for Early Sowings
I adore those sharp, sunny days in late winter through to early spring, when I’m in my greenhouse cheerfully sowing leeks or other early starters with my dog at my feet – both of us enjoying that little boost of solar warmth through the glass.
Heating a greenhouse or polytunnel is expensive, so early sowings are best brought indoors to germinate. You can use any warm place, such as on top of the freezer or in an airing cupboard, to start off seeds – just pop the pots or trays under a propagator lid or into a plastic bag to keep humidity high. My number-one favourite place to start early seeds is on my mantelpiece, with the wood-burning stove gently warming them from below.
Once germinated, hardy seedlings such as onions, leeks and cabbage family plants can be sent straight out to the greenhouse to grow on in good light. Drape them with garden fleece or plastic covers if they need extra protection from the cold.
More tender seedlings such as tomatoes will need to remain indoors until the weather warms up.
Greenhouse Growing in Summer
As winter melts into spring, keep sowing in trays and pots for transplanting outdoors later on. Catch crops of lettuces, carrots, radishes and beetroots can also be sown direct into greenhouse borders for a small harvest a little earlier than their outdoor-sown brethren.
As summer approaches, you’ll need to start transplanting container-grown seedlings outdoors to help free up space under cover. Keep an eye on the weather forecast and be ready with fleece to protect transplants if there’s a chance of a cold snap after they’ve been planted outdoors.
Once it’s mild enough, plant tomatoes, peppers, cucumbers and aubergines into greenhouse borders, containers, or in growing bags. You can also use the greenhouse as a halfway house for hardening off before planting out into your garden beds.
Summer is an intensive time in the greenhouse. I’m not going to lie – greenhouse crops require more care than those outside. Watering, feeding and pest control all need a careful eye. As the weather heats up it’s important to pay attention to ventilation, shading and damping down too – take a look at Ben’s article on How to Keep Your Greenhouse Cool in Summer for tips.
Warmth-loving but fast-growing crops such as squashes and beans can be started in the greenhouse before being moved outside, or why not try growing them under cover all summer to see if you can improve your harvest? I’ve had exceptional success growing climbing French beans in my greenhouse where they enjoy the heat and protection from strong winds.
If the weather turns wet when you harvest your onions or garlic, stack them in trays in the greenhouse to cure. This also works for pumpkins and winter squashes later on. Or why not plant potatoes in containers for a Christmas crop?
Growing Under Cover to Extend the Season
Long before those summer harvests are over, it’s time to start off your autumn and winter crops. This period can be just as hectic as the late spring/early summer changeover, and requires careful planning to ensure that you have the space to fit everything in. When summer crops are finished, borders, pots and growing bags can be reused for salad seedlings, for instance a late crop of rocket, spinach, winter varieties of lettuce, or chard.
Once the excitement of the main growing season is past, it’s time to perform some greenhouse maintenance. Make sure your greenhouse is windproof, and if you expect severely cold weather over winter, fix horticultural bubble wrap to the inside of the panes to insulate the structure. Plants can be further protected from low temperatures using fleece or plastic bottles with the bottom cut out.
You can also bring herbs such as chives under cover over winter to ensure fresh pickings for longer, or you can force an early crop of strawberries by bringing them into the greenhouse in late winter. If your greenhouse is large enough you can even use it to grow less hardy fruits such as peaches, nectarines, figs or grapes.
One other benefit of a greenhouse is that it can be used to store compost and other growing media in winter, keeping your potting mix ingredients on hand – and not frozen! – when you need them. Draping them with hessian or fleece will help prevent freezing if the weather is very cold.
What are your favourite ways to make the most of your greenhouse or polytunnel? Let us know by leaving a comment below.