Gardening calendar 2021 – what to grow in your greenhouse each month

One pastime that has definitely regained popularity throughout this year is growing our own vegetables. And many of us are ready to welcome 2021 and start planning for the year ahead – which is where our gardening calendar comes in. 

If growing your own fresh, seasonal produce is something that you would like to continue, Nelly Hall, Brand Director at British greenhouse manufacturer, Alitex, gives her recommendations on what to grow in a greenhouse – or summerhouse – each month to help you plan for a thriving kitchen-garden.

'We were delighted to see so many people trying their hands at growing during lockdown,' says Tom Hall, owner and managing director of Alitex.

'Growing your own produce has huge benefits for both our physical and mental health, and undoubtedly, homegrown veg is always tastier! A greenhouse enables gardeners to extend the seasons and produce good crops of a wide range of vegetables.'

Gardening calendar 2021

Use our month-by-month gardening calendar to grow your own successfully.

January

Towards the end of the month, you can think about sowing hardy salads and oriental greens such as mustard greens, pak choi or winter varieties of lettuce. 

If you have early sowings of sweet peas or onions, now is a good time to pinch them out and plant them into larger pots. 

Make sure any compost used for sowing or potting is brought into the greenhouse to warm up several days before it is used to prevent seeds and young plants being chilled.

February

You can sow a bit more this month to get a headstart before spring – early carrots, salad leaves and spinach are ideal for early spring picking. 

February is also the time to encourage potatoes to sprout before planting – a process known as chitting.

See more: How to grow potatoes – a step-by-step guide

March

Early spring can bring wide temperature fluctuations that can be a problem – a bright sunny day at the end of the month can result in the greenhouse overheating. Aim to keep the air temperature between 7 and 18°C; this will involve heating the greenhouse at night and also ventilating and damping down during sunny days. Keeping the door and vents open more frequently as the month progresses helps to keep humidity levels down and prevent disease. 

Large-seeded, large-leaved vegetables such as cucumbers and zucchini/courgettes can be planted into their own individual pots and placed in a propagator. In about a month from sowing, the pots can be moved into the main body of the greenhouse for an early July harvest. 

Sow a tray thickly with peas for a quick crop of shoots. Keep the tray well-watered and turn it daily to prevent the shoots from turning towards the light. Sow broad beans in cardboard tubes to make planting out easy. Water regularly, and again, turn them so that they grow straight. 

April

April is a busy time in the vegetable garden, as lots of seeds can be sown this month. Now that the days are longer and warmer, you can start sowing crops such as carrots or peas outside. More tender crops like aubergines and courgettes, still need to be sown under glass. 

Sow leek seeds into a deep pot to germinate. Leeks are hardy, but slow growing, so plant them now to harvest in the winter. 

Sow runner beans into deep modules and keep them warm and moist. Water every 2-3 days. 

May

By late May most risk of frost has passed, so many seeds can now be sown directly outdoors, but there’s still plenty to plant in the greenhouse. 

If you’re new to growing vegetables, beetroot is a good, easy-to-grow option; the seeds don’t need much encouragement to germinate and they require little maintenance once established. Dwarf French Beans are also easy to grow and produce a good harvest, but they need warmth to germinate and cannot survive frost. They should be ready to transplant from the greenhouse to the raised bed in 4-6 weeks. 

Nothing is better than a buttery corn on the cob in summer. May is the last time to sow sweetcorn, to give them plenty of time to grow and ripen. 

Kale will grow well in colder weather, but seeds will need to be started off in the greenhouse in May to be harvested throughout winter.

June

Peas are one of mice’s favourite snacks, so growing seeds in the greenhouse will offer protection until they shoot. Peas don’t root deeply, so will grow well in newspaper pots or in yoghurt pots with drainage holes added.

July

Winter Lettuces such as ‘May King’, ‘Veneziana’ and ‘Winter Density’ will only actually crop during the winter months if they are kept in the greenhouse. Sow fresh seeds into an old ice cream tub, but separate them later in the month so that the plants have more space to develop.

August

For a colorful autumn crop, sow some Swiss Chard seeds now. Our favorite varieties are ‘Bright Lights’, “Magenta Sunset’ and ‘Rhubarb Chard’.

September

Tatsoi is an Asian vegetable that’s similar to Cabbage, but more delicately flavoured and easier to grow – what’s not to love?! Sowing at this time of year – with the shorter, cooler days beginning – you dramatically reduce the risk of the plants ‘bolting’, which makes the leaves bitter and unpalatable.

October

Herbs such as basil, dill, chives and parsley can be sown now and grown throughout the winter. Under a cloche, you can grow spring onions that’ll be ready to start harvesting in the spring. 

Sowing cauliflowers now will also give you a springtime crop.

November

November is a great time to plant – and harvest! – some Microgreens. 

Microgreens are essentially small versions of the mature plant, that are cut as soon as they develop their first pair of leaves that look like that of the adult plant. 

They are nutritious and intensely flavoured and can be harvested with scissors, just as you would with cress, in as little as a week. Re-sow regularly to keep supplies topped up all throughout the winter months. Some varieties to try are beetroot, broad beans, coriander, peas, radishes, rocket, spinach and swiss chard.

December

If your greenhouse is heated, you can sow heat-loving crops like tomatoes, peppers and chillies. If not, use this month to ensure the greenhouse is clean and tidy, and plan for the year ahead.

See more: How to grow tomatoes - the best ways to grow your own tomato plants

Thanks to Alitex