Warmer Winters Have Increased Winter Vegetable Production Opportunities For UK Gardeners. Especially Where Crops Relish Colder Weather. Learn How To Grow Winter Salads in Unheated Greenhouses & Tunnels.

Mizuna ready for winter cropping 55 days after sowing. This is how to grow Winter Salads in Unheated Greenhouses
Mizuna ready for winter cropping 55 days after sowing.
Mizuna is typical crop of the crops that thrive in unheated greenhouses and tunnels. The crop in the photograph is ready for harvest on November 20th. It was sown on September 20th. It demonstrates how it’s easy to Grow Winter Salads in Unheated Greenhouses & Tunnels here in the U.K. It’s gone from seed to harvest in 55 days in ambient temperatures … ie without additional heat during the propagation or growing periods.  The crop isn’t dense but it doesn’t need to be as it’ll not be all harvested today. The plan is to harvest the outer leaves now and keep coming back to harvest more. Compared with a single harvest regime this provides regular cropping over an extended period and results increased total yield over the whole winter. It’s a very productive technique. It’s ideal where the plants may need to tolerate frost from time to time. Smaller, compact plants, grown in colder conditions are far more tolerant of frost than soft grown lush growth which often dies, or succumbs to pests and diseases.  

Sowing Winter Salads in Unheated Greenhouses & Tunnels

Seedlings growing in homemade peat free compost
Seedlings growing in homemade peat free compost
For maximum yield I recommend starting seeds in modules for later transplanting.  This technique saves cropping area.  They can be used to replace exhausted crops with large plants that produce much quicker than if we grew in situ from seed. As can be seen from the photo it’s easy to grow a wide mix of plant varieties in just one module tray.  Module plugs are then transplanted at the optimum size to maintain cropping.  

Which Species & Varieties Are Best ForWinter Salads in Unheated Greenhouses & Tunnel Production?

I’m often asked what grows best in winter. The answer depends on many factors and I frequently find that light levels are more important than temperature. Plants can often tolerate low temperatures but can’t cope with low light levels. Seed companies haven’t really caught up on the winter growing trend and play it safe with their advice.  So often they’ll recommend sowing in, say, autumn and again in March but not in between.  The reality is many plants will cope well with being sown at anytime when the temperature is above 5-6C. Others may need temperatures above 10C.  The critical factor isn’t the need for warmth once germinated but the temperature needed for germination.
Assorted seed for winter sowing test to ascertain germination and growing potential.
Assorted seed for winter sowing test to ascertain germination and growing potential.
Some crops will germinate but are prone to bolting if sown whilst “day length” is decreasing.  But sown after the solstice, with daylight increasing, will do well. The only way to be certain about these things is to test it for yourself … or let me do it for you! So I’ve sown eleven different plants on November 20th.  They are being left in a cold greenhouse and I’ll report on how they do.  I’ll sow more seeds in late winter to so how they manage.  

Winter Salads Experiment Details & Results

Please note that this experiment is being carried out in Sidmouth, Devon. Results in other parts of the country will undoubtedly vary due to climate, temperature, altitude, prevailing winds etc. These are the species/varieties currently being tested.
Species/Variety Sowing DateAmbient Germination SuccessDays to GerminateHarvest CommencedDays to Harvest
Pak Choi20/9/215
Chinese Cabbage20/9/215
Oriental \Mustards20/11/21
Oriental golden Frills20/11/21
Oriental Komatsuna20/11/21
Bucks Horn Plantain20/11/21
Kailan Kichi 20/11/21
Oriental Ruby Streaks20/11/21
Red Oracle20/11/21
Oriental Sessatina20/11/21
Oriental Wasabina20/11/21
Wasabi rocket20/11/21
Amaranth Red Army20/11/21
Basil 20/9/21
As the experiment proceeds I’ll regularly report back here.   There’s more information on growing winter salads via the following links.  
How To Grow Winter Salads and Leaves in Greenhouses, Tunnels and under Cloches in The UK
What To Grow In Winter: Sprouted Seeds, Microgreens & Baby Plants

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