How to Keep Your Greenhouse or Polytunnel Productive Over Winter: What to Sow in August
By the time August has arrived, we should be enjoying our fantastic harvests after all our hard work in the garden. But we can’t be complacent - now is the time to be thinking about how we can keep being productive in winter and planning what to sow to make the most of the cooler temperatures. Polytunnels are an invaluable resource in the cold winter months, whilst greenhouses can also offer vital protection and warmth. With a bit of work, we can have good, fresh produce throughout the winter and we can also fill the hungry gap in spring.
How to Prepare Your Greenhouse or Polytunnel for Winter
As you start clearing some of the plants in your polytunnel or greenhouse, it’s time to get preparing your space for winter growing. There are three main tasks we need to consider before the cold weather hits:
1. Cleaning your polytunnel or greenhouse
With fewer daylight hours and weaker sunlight, making sure the glass or polythene is clean and clear of algae and debris is essential to a productive winter growing season.
2. Repairing your polytunnel or greenhouse
Any cracks or tears can let the cold and the wind in, which can damage the plants and cause big issues for polytunnels in windy weather. Repair any damage to the structure, seal any gaps, and tighten the doors to give your plants the best chance of thriving.
3. Improving the soil in your polytunnel or greenhouse
Good quality, nutrient-rich soil will hold warmth much better. Make sure you’ve cleared out your spent plants, and add some refreshed compost and/or well-rotted manure to your growing space.
What to Sow in August for Autumn and Winter Harvests
The right crops sown in August can absolutely thrive through winter, and there are various different types to fill our produce gaps. Some are quick growers that will crop for longer in the heat of a polytunnel; some varieties actually taste better once the colder weather has hit; and some vegetables are perfect for overwintering, meaning that they’ll be ready to spring into action once the weather starts to warm up the following year. It’s worth noting that plant growth slows considerably as the daylight hours decrease and the temperatures start to drop, so it’s important to get your seeds sown earlier to let their roots establish before the cold hits. This will lead to stronger, more productive plants.
Here are a few of our favourite vegetables to get sowing in late summer to give you fresh produce all year round.
Autumn & Winter Salad Leaves
There are some fantastic salad varieties that you can sow through the end of summer and into the autumn that you can harvest throughout the winter months. They will be slower to grow in the cold, but with the right maintenance, they will keep producing. We have two winter salad bundles available to help you make the most of the season this year.
This contains Corn Salad ‘Lamb’s Lettuce’, Rocket Cultivated, Mustard ‘Mizuna’, and Claytonia. These are all hardy salad leaves that can be grown outdoors through the cooler months, and will happily grow in a greenhouse or polytunnel too.
This contains ‘Maravilla de Verano’, ‘Little Gem’, and ‘Salad Bowl Green’ lettuces, all of which are perfect for growing in a greenhouse or polytunnel to produce a fresh supply of leaves during autumn and winter.
Autumn & Winter Vegetables
There are plenty of vegetables that will keep producing into the winter months, and many varieties that take a relatively short time to mature. Others are perfect for giving you produce in the early spring when fresh food is in short supply.
Our Autumn & Winter Veg Bundle combines some of the best vegetables for growing and harvesting throughout the cooler months, and they will all grow well under cover. It contains Kale ‘Nero di Toscana’, Spring Onion ‘Snow Queen’, Broad Bean ‘Aquadulce Claudia’, Spinach ‘Medania’, Fennel ‘Florence’, and Cabbage ‘Red Drumhead’.
Autumn & Winter Asian Leafy Greens
Asian leafy greens are remarkably quick growing, and can be sown in late summer and early autumn, making them an excellent choice for winter produce. They thrive in the sheltered conditions of a polytunnel or greenhouse, and are perfect for salads, stir-fries, and steaming.
Our Autumn & Winter Asian Leafy Greens Bundle brings together some of the best varieties for growing under cover during cooler months. It contains Mustard ‘Tatsoi’, Pak Choi ‘Red’, Chinese Cabbage ‘Michihili’, and Mustard ‘Mizuna’.
Autumn & Winter Herbs
While herbs often make us think of summer cuisine and warm weather, there are various types that will do well in winter when sown in a polytunnel. The cooler weather can also help some varieties that are prone to bolting, giving you fresh herbs for longer.
Our Autumn & Winter Herbs Bundle brings some of the most productive herbs for colder weather together, and is perfect for polytunnel and greenhouse growing. It contains Coriander, Sorrel ‘Lemon De Belleville’, Parsley ‘Italian Giant’ and ‘Chervil’.
Autumn & Winter Root Crops
There are lots of root crops that can still be grown from August and into the winter months. Some crop very quickly, like radishes and turnips, whilst others will taste sweeter thanks to the colder temperatures.
Some of our favourites include Radish ‘China Rose’, Beetroot ‘Boltardy’, Turnip ‘Milan Purple’, and late-season carrots like ‘Autumn King 2’.
How to Care for Winter Crops in a Greenhouse or Polytunnel
Whilst a polytunnel or greenhouse will offer a good level of protection for your plants, there will still be some work to do to keep your vegetables happy during the colder months. Here are a few of our top tips for keeping your produce safe this winter.
1. Don't Forget to Ventilate
It can be very easy to think that keeping everything closed up is for the best, but this can lead to higher humidity and encourage damp, mould, and mildew. Ventilate your greenhouse or polytunnel on milder days to increase air circulation and keep your plants healthier.
2. Water Less
Without as much heat to evaporate the water, it can be easy to fall into the trap of overwatering. Avoid leaving the compost saturated as this can invite disease, and try and water during the morning if you can. Make sure you check your containers too.
3. Protect Against Frost
Although your plants will be protected from a lot of winter’s harsher elements, you will still need to watch for sudden cold snaps. Even in a polytunnel or greenhouse, frosts can be devastating. The glass of the greenhouse is also prone to conducting the cold temperatures, so extra protection can be a necessity. Try horticultural fleece to take the chill off, and be sure to close any doors or vents in the evening. Placing a water barrel or a large, dark rock inside your structure can also be a great way of regulating the temperature. They will draw heat in during the day and steadily release it throughout the night.
4. Keep an Eye Out for Pests
A lot of people don’t really consider pests during the winter as they have often died off in the cold weather. However, creating a warmer environment for your crops can attract some unwanted friends like aphids, and slugs can be an issue year-round due to their love of damp conditions. Check our recent guides to aphids and slugs in the garden for some tips on how to deal with these pests.
