What to Grow in the Polytunnel in Winter

While winter growing is 'totally a thing' (as my daughter would say), it can be misunderstood to mean that summer crops can be grown undercover in winter - which is certainly not the case! Winter in a polytunnel or greenhouse is more about protection from the elements than an increase in temperature (though it can get warm on a sunny day), so it is still only cold-tolerant crops that grow (very slowly) in the middle of winter.

We need to remember that available light plays a big part in cold season growth: this means both light intensity and the total amount of daylight hours, both of which will be very low from November to January.

Winter in the polytunnel is more about sowing and planting in August and September to have crops large enough to pick over winter. This predominantly includes leafy crops like cold tolerant Asian greens (e.g. mizuna, rocket and mustard greens), lettuce or chard. Despite slow growth, you can reap a very welcome and valuable supply of greens through the three coldest months.

It depends what the weather is like, but it is probably best to germinate seeds in a propagator or on a windowsill in the house before planting out in the tunnel beds. As regards growth, again it depends on outside temperatures, but it can be helpful to use a cloche or mini tunnel inside the main tunnel for a double glazing effect and some extra warmth.

Giant Easy Fleece Tunnel - Plant Protection

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You can also sow early carrots in a tunnel, which will do well if the winter is mild but will struggle if it's cold. I will confess that I have never tried this in November, but have done a late January sowing with great success. I may put in a few seeds this weekend and see what happens.

What to Sow in the Polytunnel in Autumn

1 - Annual Spinach
2 - Asian Salads
3 - Claytonia
4 - Lamb's Lettuce
5 - Chard & Perpetual Spinach
6 - Lettuce
7 - Kohlrabi
8 - Florence Fennel
9 - Spring Cabbage
10 - Beetroot
11 - Winter Radish
12 - Turnip
13 - Calabrese
14 - Garlic
15 - Peas
16 - Early Carrots
17 - Broad Beans

Apart from the harvesting of existing crops (in my case: sweet peppers, chili peppers, tomatoes, squash, courgette, lettuce and French beans) there is still plenty to sow in the polytunnel in autumn, either for winter harvests or for crops next spring. Here's a quick run down of what I will be doing over the next 6-8 weeks to prepare for the next part of the growing season:

Annual Spinach

Spinach can be sown up until mid September. I find the third week of August best to get decent size plants to stand for the winter. Oriental spinach (e.g. Mikado) is very good for late sowings.

Asian Greens

Asian Greens - sometimes referred to as Oriental Salads - offer a vast range of cold tolerant salad crops which form the backbone of the midwinter polytunnel. They provide a mix of flavours from peppery (Osaka, leaf mustard) to mild (red or green mizuna) to crisp and juicy like pak choi or Chinese cabbage.

Sow from late August to early October. 

Pak Choi 'Karaoke' - Asian Brassica

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Claytonia and Lamb's Lettuce

Apart from the cold hardy Asian greens, the other stars of the winter polytunnel are Claytonia (also known as miner's lettuce or winter purslane) and lamb's lettuce (aka corn salad or mâche). Both are cool season salad crops, and both taste great.

The distinctive Claytonia has rounded or heart shaped leaves, while the stem extends outwards bearing delicate white flowers.

The fleshy leaves can be eaten raw or lightly steamed or sauteed, while the flowers and stems are also edible.

Lamb's lettuce is one of the hardiest salad vegetables you can grow (it can even withstand frosts outdoors), and will produce leaves - albeit slowly the further we go into winter - into early spring. These leaves have a mild and slightly nutty flavour, and are borne on clusters of compact rosettes.

Corn Salad 'Verte a Coeur Plein 2'

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With lamb's lettuce you can harvest leaves for repeat pickings or cut and harvest the rosettes as some people prefer. Both Claytonia and lamb's lettuce are adept self-seeders which is something to be aware of if you are letting them flower. 

Sow both from August to October.

Chard or Perpetual Spinach

Chard or perpetual spinach sown in mid to late August will produce a good size leafy plant that will produce new leaves until November. It can be picked over winter and will shoot off again in February. 

If you like the flavour of chard this is a fantastic indoor winter crop. Grow Rainbow Chard for fantastic brightly coloured stems or Swiss chard for a milder flavour. Perpetual spinach, meanwhile, does as its name suggests and keeps producing leaves as you pick them.

Lettuce

There are particular varieties that survive cold better than others, but in my climate I find most lettuce will stand well over winter. If you have a cold spell you can always cover them with fleece. Sow until mid-August for decent size plants, before growth almost stops in November.

KohlRabi

An outdoor vegetable in summer, but it does very well in the polytunnel from an August sowing. It can also be sown as early as late January for early spring crops.

Purple kohlrabi is recommended over green varieties for autumn sowings, as it is more cold tolerant.

Envirofleece Heavy Duty Winter Garden Fleece 30 g

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Florence Fennel

An early August sowing of Florence fennel works best for me to get some good size bulbs before November, but in milder areas fennel does overwinter well. It does suffer from frost so (like lettuce), cover with fleece on cold nights. For milder areas you can sow up to early September.

Spring Cabbage

Spring cabbages are best sown before the end of August and planted out in the polytunnel in late September, for harvests from late February to mid April the following year. F1 hybrid Caraflex is a particularly good choice here.

Beetroot

For an early spring crop, beetroot is best sown in early August - but it can also be sown as early as February for spring harvests.

Winter Radish

Winter radishes can be a real treat, especially the white mooli varieties: they are sweet and juicy and are ideal late season crops in the polytunnel. Sow in mid August for good roots over winter.

Radish 'Daikon'

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Turnip

Opt for a fast growing variety like Turnip Polar, which can be sown as late as September and rewards you with a high yield of white skinned turnips just 5 weeks later.

Calabrese

Preferably sow in early August for planting in September. Calabrese broccoli (that's the one with the big green head!) will stand for the winter and start to produce heads in February.

Garlic

Plant cloves in October for harvest the following June. 

Related Article: Overwintering Garlic and Onions

Peas

Early peas can be sown in October - if you can afford the space the following spring. They are harvested in April and May.

Early Carrots

Carrots can be sown in October and November (or in January and February next year) for an early polytunnel crop. I usually sow in late January, and had a very good crop in early June this year. I will try an October sowing this year and let you know how I get on.

As with the other overwinter sowings, space is the deciding factor, especially in a polytunnel, as you don't want space taken up with carrots when you need to get something else going. If all goes well, you can get a crop of decent size baby carrots before you need the space for tomatoes etc, but you won't have time for a full size crop.

The variety you sow must be an early one e.g. Amsterdam Forcing as they will be less likely to bolt.

Broad Beans

For an extra early crop if you have the space, sow in November or December in trays and plant out 3-4 weeks later. Harvest in April and May.