Growing Under Cover All Year Round

, written by gb flag

Lettuces thriving in a greenhouse in a frosty winter garden

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.

Greenhouse seedlings protected with garden fleece

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.

Busy summer greenhouse full of crops

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 climbing beans in a greenhouse

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.

Bottle cloches protecting seedlings in a greenhouse in winter

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 burlap/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 tunnel? Let us know by leaving a comment below.

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Show Comments


"How do i warm my greenhouse if i'm using them on my back glass enclosed back patio room to place them in? someone told me i should use heat lamps? "
Carlene on Friday 3 February 2017
"Hi Carlene, if you're using a small greenhouse indoors then most crops won't need additional heating. However if you're starting seedlings in it, some may benefit from the bottom heat of an electric propagator, or alternatively placing seedlings under grow lights early in the season can also provide a small amount of supplemental warmth. "
Ann Marie Hendry on Tuesday 7 February 2017
"We have some garden beds in our covered in carport area which also has an outdoor entertainment area. There is filtered light through shade cloth the length of the garden beds. I have planted snap peas, they are thriving. Two lots of green beans have disappeared. Lettuces not doing much chives and spring onions not too bad. We have had to further cover the gardens with bird netting because the cat wants to dig it up. There are sprinklers above these beds. Can you suggest other veg to sow there please."
Maree on Friday 20 October 2017
"Hi Maree, it's difficult to advise without seeing your growing area but if it's sheltered with light shade then you could try crops such as carrots, beetroot (beets), spinach, broccoli, cabbages and turnips. If it's too warm in summer, leafy crops such as lettuce might struggle, but they should grow better in spring and autumn. It would be worth experimenting with small plantings of your favourite vegetables to see what works well. "
Ann Marie Hendry on Wednesday 25 October 2017
"I have a greenhouse that I bought from bunnings. It is the steel bar frame with the plastic covering and has a zipper on either side of the door. Im new at this and wanted to know .... I planted pumpkin seeds in July, they've germinated. I wanted to know if I can leave them in the greenhouse till they are ready for harvest, or when should i remove and plant in the ground. I get confused when I look it up on the net as some sites are for USA when Im searching for Australia. Regards, Gina 9th August, 2018."
Georgina Likidis on Thursday 9 August 2018
"Hi Gina. Unless your greenhouse is quite large, it's probably best to grow your pumpkins outside - they produce vines that can often reach for several metres! Our Garden Planner can recommend the best times for sowing and planting out in your specific location - click on Garden Planner at the top of the page for a free trial."
Ann Marie Hendry on Saturday 11 August 2018
"If a green house extends my growing season, is there a feature in the software to account for this? There should be a "green house" button that I can check, which will extend planting and harvest recommendations in the plant list. Also, for every layer (a green house plus row cover) added, the climate inside the green house moves to a higher zone level. This would be a great feature to add to the software."
Andrew Glover on Sunday 7 October 2018
"Hi Andrew. You can find greenhouses, row covers, cold frames etc in our range of garden objects. To locate these, click on the selection bar drop-down menu then click on Garden Objects. The plants in the selection bar will then be replaced by garden structures, paving and other items as well as season extenders. Adding a greenhouse or other season extender to your plan will automatically extend your growing season for the plants grown within it. If you have any questions about this, please get in touch with our friendly customer support team by clicking on the Contact button at the top of the page. We're available 7 days a week and always happy to help. "
Ann Marie Hendry on Tuesday 9 October 2018
"Thank you! This article is just what I was looking for. "
Kel on Friday 3 April 2020
"Hello, I purchased a home a few years back that came with a very large greenhouse. This is the first year I am utilizing it and looking to add some heat for year round growing. I am located in Pennsylvania, US. Can anyone recomend a heat source that would work? would directional heaters work for hanging over the plants? "
Hillary on Wednesday 1 July 2020
"Glad you found it useful Kel!"
Ann Marie Hendry on Friday 3 July 2020
"Hillary, because heat rises, suspending a heater over the plants will be of less benefit than having it on the ground. You can buy gas, electric and paraffin heaters specifically designed for use in greenhouses. Be warned though, heating a greenhouse is said to be very expensive, so you might want to take running costs into account when choosing a heat source."
Ann Marie Hendry on Friday 3 July 2020
"last winter, we discovered Texas can lose its ability to heat our homes. One suggestion that came was to use a candle under a terracotta pot. A small amount of heat escapes through to drainage hole, but the pot warms and radiates heat to the room. It might work for a small insulated greenhouse."
Mary c laura on Thursday 9 December 2021
"Great suggestion Mary. I have actually tried that in the past, but my problem was that my terracotta pots were quite small and therefore the candles were too, and didn't burn all night. If you had a large enough pot and candle though it could well help to keep a small greenhouse frost-free."
Ann Marie Hendry on Thursday 9 December 2021

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