Winter Seed Sowing on Cold and Frozen Soil

Rebecca Smith
Wednesday, 22nd January 2020

Cold climates can shorten the growing season, especially making seed sowing difficult. Rebecca Smith shares her adapted method, inspired by blogger, Sara Bäckmo, to sowing seeds in cold weather, for spring harvests.

I live in Norway, at 60 degrees north, where the growing season is short due to our latitude. However, I live on the coast where the climate is mild relative to the rest of Norway. It is comparable to Denmark or northern Scotland. Every January, like many gardeners in the northern hemisphere, I get the itch to sow and grow. I sow what I can into pots inside under growing lights (pea shoots, chillies, pot tomatoes, baby leaves, basil), but in 2017 I stumbled upon the concept of 'winter-sowing' ('vintersådd in Swedish and Norwegian). I came across this idea via Swedish gardener, Sara Bäckmo, on her excellent blog1 and YouTube channel.2 This allowed me to take my gardener’s itch outdoors.

Winter-sowing is a method of sowing hardy and half-hardy annuals outside directly onto frozen soils. I applied and tried out her methods straight away with varying results. Bäckmo lives in Sweden in a slightly different climate to mine. Winters where I live are milder, with less snow and sub-zero temperatures, so not everything she does in Sweden works here. After two winters of trial and error in my climate, however, I have fine-honed and adapted the method to my specifications. I think this method could work in the UK too, especially in northern climates such as Scotland, Northern Ireland and perhaps even the north of England. I recommend you watch Bäckmo’s YouTube videos on the subject, some of which are now subtitled or in spoken English. She also has a blog in English on the subject too.3

Winter sowing is advantageous because it gives early yields in April / May. It also gives a head start to seedlings in areas where slugs are a problem and frees up time in spring when gardeners are at their most busy. I remember my delight the first year I tried this and had spring onions galore as well as early carrots and fresh watercress in May. A step-by-step guide is below.

As a side note, I follow Jean-Martin Fortier’s crop rotation plan from his book, The Market Gardener.4 I have noticed that, with the exception of spring onions, the majority of varieties suitable for winter-sowing belong to the 'greens and roots' crop rotation category. This is useful, because in the autumn I can prepare the beds earmarked for 'greens and roots (and Liliaceae for spring onions) in the following year.

How to winter-sow

Prepare beds (greens, roots and Liliaceae) during mild spells in autumn (September, October, November, December and January at the latest). Weed the beds, aerate and rake the soil, fertilize if necessary and cover preferably with a porous fibre weed-suppressing cloth. This allows rain to filter through and incorporate any fertilizer into the soil over winter, whilst suppressing weeds, preventing erosion, compaction from rain and nutrient leaching. I keep these cloths held down with old tyres.

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Cover beds to suppress weeds, prevent erosion, compaction from rain and nutrient leaching ©Rebecca Smith

Make sure you have a couple of bags of compost / potting soil stored indoors, thawed and ready to use.

Make sure you have seed varieties bought in and ready to go for January. Suggestions below.

Make sure you have glass cloches or see-through plastic frames, fleece or polythene tunnels ready. If high winds are a problem in your area, then I recommend disused aquariums, glass cloches and old door frames with plastic panels screwed onto them (see-through corrugated plastic roofing is great).

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Protect the winter-sown bed with glass cloches, plastic frames, fleece or polythene tunnels ©Rebecca Smith

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Old aquariums make good cloches in windy areas ©Rebecca Smith

Wait until a very cold snap in January, February or the beginning of March to sow. The soil has to be frozen, so sub-zero temperatures are required. If you sow too early or when the weather is mild, then you run the risk of seeds germinating but then getting killed off by cold snaps later on.

Sow seeds directly onto the frozen soil at recommended spacings or adapted intensive spacings as desired. It can get nippy sowing seeds in this weather! I use fingerless gloves and only really space out carrots and parsnips carefully. I use a seed dial to save time and frostbitten fingers for other seeds, such as turnips, spring onions and herbs. This gives a roughly correct spacing, and turnips and spring onions can be thinned out.

Cover the seeds with the thawed compost / potting soil from inside.

I recommend sprinkling ferric phosphate based slug pellets around the sown seeds at this point too. This is extra insurance because I live in an area where slugs are a huge problem and have seen them come out as early as February in sheltered spots.

If possible, top the sown bed with snow for slow release moisture. Don’t water the seed bed at this point or you will wash the carefully sown seed in all directions! Moisture content in the soil is not normally a problem for me because of high rainfall.

Cover the sown beds with glass cloches, plastic frames, fleece or polythene tunnels.

Keep an eye on the seedlings. Fine spray watering can begin once the seeds have germinated, as necessary. Depending on your climate, watering is unlikely to be necessary until late March / April when warm spells can occur. It’s recommended that the glass / plastic / fleece is removed on warm days.

Also keep an eye out for slugs and remove as soon as they are spotted.

The glass / plastic / fleece can and probably should be permanently removed before mid-April when warmer weather can set in. Bolting is likely to occur in rocket, spinach, Asian greens, dill and watercress if not. The seedlings are likely to be big enough to tolerate any late frosts at this point.

Winter sowing can also be done in cells / pots in a cold greenhouse or cold frame, for a head start on planting. Cauliflower, broccoli, pyramid cabbage, swede and kale are possibilities. The disadvantage of this is getting the watering right. It is easy to over water causing mould and fungal disease, but it is also equally as easy to under-water causing seedlings in pots to dehydrate and die.

Winter sowing is also applicable to some summer flowers. Sow into compost-filled plastic tubs with lids, perforated for rainwater entry and drainage, and set outside. Remove the lids once the seeds have germinated and plant out as soon as the seedlings are large enough. I tend to scoop out and transplant the whole tub into a flowerbed. Suggestions for varieties are below.

Suitable varieties to sow 

All varieties that are 'hardy' or 'half-hardy' or that self-sow are potentially suitable for winter sowing. Varieties that need to be sown early for stratification, such as parsnips are also suitable.

Firm favourites, tried and tested:

Dill
Parsley (flat leaved or curly)
Edible chrysanthemum
Watercress
Lettuce (Oak-leaved, Little Gem)
Summer carrots (Amsterdam forcing, Nelson, Nantes, Baby Finger)
Parsnips
Turnips (Purple-topped Milan or any other variety)
Spring onions (White Lisbon winter hardy)

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Super-early, winter-sown edible chrysanthemum. A delcious salad leaf or stir-fry vegetable. ©Rebecca Smith

Possibilities, as of yet untried"

Kale for baby leaves (all varieties)
Salsify (black or white)
Chard (Fordhook Giant)
Komatsuna mustard greens
Caraway (for young shoots and leaves, see Stephen Barstow’s book in references for recipes)
Lamb’s lettuce

Possibilities that didn’t work for me due to bolting (but might for more southerly latitudes):

Asian greens (tatsoi, choy sum, pak choi)
Rocket
Spinach (early varieties, Early Prickly Seeded) 

Summer flowers:

Pot marigold
Cosmos
Sunflowers
Annual poppy
Purpletop vervain
Garden/common mignonette
Nigella
Larkspur
Poached egg plant
Cornflowers
Californian poppy

References

1 Sara Bäckmo’s Norwegian blog: www.sarabackmo.no and the articles I first read: 'Å så i vinter og snø” 20.11.2017, “Så grønnsaker i desember' 01.12.2017, 'Overvintre mangold' 04.12.2017, 'Jeg dyrker i januar' 05.01.2018.
2 Sara Bäckmo’s English YouTube channel: www.youtube.com/c/saraskitchengarden recommended videos: 'Sow on top of the snow - sandwich vegetables' and 'Sandwich vegetables sown on snow'
3 Sara Bäckmo’s English blog: www.sarabackmo.com article: 'Winter-sowing in a cold frame' 04.01.2020
4 Fortier, J-M. 2014 The Market Gardener New Society Publishers
5 Barstow, S. 2014 Around the World in 80 Plants Permanent Publications 

Rebecca Smith is a gardener, writer, teacher and poet living on the west coast of Norway at permaculture LAND centre Seversgarden. Find and follow her on Facebook at www.facebook.com/seversgarden. Other writing and poetry is published in Permaculture Women Magazine and at wordsoftheair.wordpress.com

Useful links

Vegetables to grow in winter

Growing salads in winter

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