Winter is not all bad, depending, of course, on your climate. For someone in Florida and Arizona, winter may be the best growing season. Even here, in South West England, we can have plenty of harvests. I suggest consulting local knowledge to find out what can work in your winter months.
Winter, in meteorological terms, is a quarter of the year from December through to February. However it often feels longer, depending on your climate. Here it can feel like winter begins in November, with days suddenly brief and dark (we are 51°N), and then it ends by the March equinox, when days are suddenly very light, if not warm.
However, the effects of winter linger into the hungry gap of early to mid-spring when there are new leaves to pick but few harvests of substance – overall that is half of the year!
Winter food
Snow insulates both plants and the ground, and is less of a problem than low temperatures. Soft, dry snow, in particular, can protect the plants under it for a month and more.
In a temperate climate such as the UK, snow rarely lasts for long because of the nearby oceanic warmth.
Frost can be more problematic, but many vegetables are impressively hardy (see ‘Frost tolerance’ below). The lowest temperatures in my garden, over four decades, have been: –16°C/ 3°F (once), –14°C / 7°F (three times), –11°C / 12°F (twice, in 2010) and –7°C /19°F (most winters).
Fresh harvests in winter
In a temperate climate, there are several vegetables that you can grow through the preceding months for occasional harvests during winter – leeks, Savoy cabbage, parsnips, Brussels sprouts and kale.
Salad plants can also give small harvests, especially corn salad / lamb’s lettuce, Claytonia, salad rocket and land cress; also mustards and leaf chicory, if not too cold.
- In colder climates, you need to harvest some of these vegetables to store before it turns really cold.
Annual and biennial herbs, such as chervil, parsley and coriander, are frost hardy. They survive most winters in temperate climates and give small harvests outside, more under cover.
Some vegetables can be overwintered as small plants, to then grow fast in the spring and crop in the hungry gap. Examples are spring cabbage, spring onions, lettuce and garlic.
Storing vegetables
This is easier than sometimes described. You can eat well from stored vegetables that have grown in healthy soil – harvests of root vegetables, unwashed and kept in sacks or boxes, keep for a long time in good condition.
- In temperate climates, you can keep these vegetables in an outdoor building with minimal insulation.
- In continental climates of deep cold, it’s best to store them in a cellar.
- Potatoes harvested in July store in summer heat without sprouting, and are good to eat until early spring of the following year.
Root vegetables go soft eventually, but the flavour is still excellent. They may look wizened, but they still have great nutrition and microbes.
Likewise with apples that you store at home, which are seldom as crisp as store-bought ones yet the flavour continues to be excellent – here we are still eating apples from October harvests until late March.
For winter food, sow before
New growth in the dark and cool months is slow, while seed germination is even slower. With one or two exceptions, such as microgreens and peas for shoots, I recommend not sowing anything in December or January.
For winter harvests of fresh leaves, your summer and autumn sowings need to be at the best times. Unlike in spring, plants cannot ‘catch up’ from a late sowing date, with fading light and falling temperatures.
See the Harvesting Timeline in Lesson 14 for detailed sowing and harvesting dates.
Sowing in August
A top-performing winter vegetable is spinach, sown in the first half of August. It has star qualities in winter weather:
- It is very hardy to frost, –10°C / 14°F or lower, and most spinach should survive these temperatures.
- It continues growing in temperatures as low as 7°C / 45°F, slowly and with sweetness.
Many varieties are recommended for winter growing, and my favourite is Medania, for the following reasons:
- It has tender leaves with flavour and sweetness (dark green, at a time when you most want that), which taste excellent raw in salads.
- It is especially resistant to early bolting – 95% of plants that we sow on 10th August will crop until the following May.
You can sow three seeds per module, then thin to two plants for leaves of medium size, or to one plant for large leaves. These can be transplanted when small, two to three weeks old, at a spacing of 25 cm / 10 in. There are then harvests from late September until May, which are smaller and fewer in winter, and with sweeter leaves (see ‘Leaves’ in ‘Frost tolerance’ section below).
Sowing in September
This is the month for sowing salads to grow under cover. They crop through winter a little, and into spring a lot.
Covers such as a polytunnel or fleece enable not only better survival, but healthier and larger leaves when otherwise they would be thin and small. Plants grow more strongly in a polytunnel than under covers outside.
- Careful picking of outer leaves, instead of cutting across the top, enables plants to survive the coldest weather and then to thrive in early spring, before flowering in April and May. (See Lesson 13 for more information on harvesting leaves.)
There are three salads whose tolerance of cold is remarkable, and which are therefore the most viable for growing outside: corn salad / lamb’s lettuce (Valerianella locusta), Claytonia (Claytonia perfoliata), and American land cress (Barbara verna).
Sowing just before winter
I recommend sowing broad beans in modules from late October to early November, or outside in late October. Module sowing is worthwhile because of mice, which eat the seeds, and birds, which pull up seedlings to eat the sprouted seeds. I have had this happen often enough to make me willing to do the extra work of raising plants. Also, broad beans are valuable – they are early to crop and have wonderful flavour.
In a colder climate than here, you can sow broad beans in mid-October for planting out in November. I was contacted by a man from Western (maritime) Norway who succeeds with this. You want plants no taller than 10 cm / 4 in in midwinter, so that they are hardy to winter weather.
Sometimes plants do not survive the winter; this is to do with humidity, as well as low temperatures and a lack of snow. In this case, you could make a January sowing under cover, for transplanting in early March with fleece over.
The previous chapter has information on using covers to protect plants from frost, wind and other winter weather. Winter plants grow more strongly under a cover, and are protected from pests. They are worth a try if your location is not too windy.
Frost tolerance
This section looks at frost tolerance, both by vegetable type and by family, to help you gain a full understanding. I want to reassure you about vegetables that survive freezing, to clarify which ones don’t, and also to demonstrate how vegetables can be more or less sensitive to freezing depending on their stage of growth.
By type
Many leaves are frost resistant, most fruits are not. Root harvests survive some frost at least, except for potatoes.
LEAVES
These vegetables do not look happy when frozen, and you might even think they are damaged irretrievably. However, once thawed, they regain lustre.
Freezing can actually augment the value of some harvests. Leaf vegetables, such as spinach and kale, grow sweeter in any cold weather, thanks to their conversion of starch to sugar as a built-in method of frost protection. Many winter vegetables do this to some degree, and have a higher sugar content after frosty weather. The process continues in a cold spring, even in April. After spring frosts, the sweetness is striking.
ROOTS
What are commonly called ‘root vegetables’ include many with swollen stems – some types of radish, Florence fennel, beetroot, kohlrabi, celeriac and swede. The part that is harvested is at or above ground level, making them more exposed to frost.
Root vegetables whose edible part is mostly below ground are more protected against freezing. They vary in terms of frost resistance – potatoes are susceptible to any hint of freezing, carrots are damaged only if they freeze solid, while parsnips survive a solid freeze and grow sweeter from it.
HEARTS AND SHOOTS
Frost causes more damage to tight hearts than to loose leaves, but only when it’s cold enough to freeze into the middle. Hearting vegetables should stand frosts of–°2 to –3°C / 27°F. Cover beds with fleece for extra peace of mind.
Broccoli shoots are hardy, mostly. The occurrence and amount of damage depends on the duration of the freeze, as well as the lowest temperature.
Cauliflower plants are frost hardy and the curds survive slight frosts. Before moderate frost you can lay an outer leaf over them to reduce the risk of damage.
FRUITS
Most fruiting vegetable plants are not only destroyedby any freezing, but need heat to grow and thrive. Plants of runner and French beans, cucumbers, squash, aubergines, peppers and sweetcorn look small and sad in cool weather, even if not being killed by frost. Tomato plants may survive a slight frost (see also Legumes below).
By family (see table in Lesson 4)
ALLIUMS
These are all hardy to frost, especially garlic and leeks. Garlic actually needs a slight freeze, to trigger differentiation into cloves during the following spring.
The long stems of summer leeks that are above ground go soft after frosts of about –4°C / 25°F. Winter leeks stand less above ground level and can be earthed up; they also have more dry matter, and varieties such as Musselburgh, bred in Scotland, are hardy to deep frost.
Green or spring onions are tender to eat and look fragile, but they resist low temperatures. The photos, above, show progression of the same planting, from 19th March to 29th March.
Seedlings of onions and leeks survive freezing. However, if this happens during their first weeks of life it can result in them bolting – they think that winter has happened and that they are in their second year of growing, when they rise to flower for seeds. The best remedy is to sow a little later.
ASTERS
These are frost-hardy vegetables, but there is some risk of damage to leaves, such as the tips of young lettuce leaves turning brown where they touch mesh or fleece covers in frost. Covers are mainly for protection against pest and wind.
Chicory is more frost hardy than endive, which in turn is more frost hardy than lettuce. Small plants survive freezing better, compared to when they are at the hearting stage.
Frost, and also old age, may cause leaves to decay, but this is not always a reason to despair. I find it fascinating to trim chicory hearts and to discover the hidden treasure within, as in the photos, below, of a 206TT Treviso type in late autumn.
BRASSICAS
Many brassica plants survive temperatures below –10°C / 14°F. The hardiest brassicas are Brussels sprouts, kale and Savoy cabbage. Curly kale survives extreme cold better than flat-leaved kales like Cavolo Nero.
Of brassica root vegetables, swedes are the best survivors in really cold weather. Kohlrabi stay in good condition down to about –5°C / 23°F, but turnips are more watery and need harvesting before, say, –3°C / 27°F.
Leaves of many brassicas survive to –15°C / 5°F or lower. The hardiest salad brassica is land cress. I only wish it tasted less pungent so that we could eat more of it!
Loose leaves suffer less damage when frozen than do tight hearts, which can split open. Hearts with crinkly leaves, such as Savoy and Chinese cabbage, survive some freezing.
CHENOPODS
This family of plants is reasonably frost hardy, especially spinach, as I explain above. Chard plants do not survive freezing as well as spinach, perhaps only down to –5°C / 23°F. Often, if the temperature gets lower than this, the roots turn to mush – plants may struggle on but are not worth trying to save.
Beetroot in late autumn also stand to about –5°C / 23°F. If your climate is regularly colder than this in late autumn, I would harvest beetroot and keep them in a shed, where there may still be some frost, just less than outside.
Seedlings of beetroot and chard in spring time resist freezing and then grow again. However, this level of cold can result in plants bolting, as with seedlings of onions and leeks (see ‘Alliums’ above).
CUCURBITS
All plants in this family are likely to die after the slightest frost. They also require warmth to make worthwhile growth.
LEGUMES
There is a huge range of frost tolerance within this family.
Broad beans as small plants, say, 5 cm / 2 in high, survive to –10°C / 14°F and perhaps even lower.
Plants of peas and broad beans can thrive in quite cool weather, when nights freeze a little. In a late spring frost, their pods may also partially freeze without damage, at temperatures no lower than about –2°C / 28°F.
In our climate, a sowing of peas in modules around the middle of October, then transplanted in the polytunnel, can survive winter frosts to about –6°C / 21°F. There are then harvests of pea shoots from December until May; however, this does not work outside.
Similarly, you can sow sweet peas in November to grow under cover through winter and then transplant outside in March. They are frost hardy, and should flower by May.
It’s vital to know that some legumes, such as French and runner beans, are killed by even a slight frost. Moreover, they simply do not grow when soil temperatures are below about 15°C / 59°F.
SOLANUMS
Early potato growth is singed by a slight frost or blackened to mush by a hard frost. Before any forecast of frost, covering potato leaves is worthwhile.
Potato plants do grow in cool conditions, which marks them out from their solanum relatives. Tomatoes, aubergines, peppers and chillies all need warmth to grow, as well as being very susceptible to frost.
UMBELLIFERS
All of these survive frost, to a greater or lesser degree. The order of frost hardiness, with the more susceptible plants listed first, is celery, dill, Florence fennel, coriander, carrot, celeriac, chervil, parsnip.
Plants of Florence fennel survive brief frosts when small, a –3°C / 27°F dawn in April, for example. However, the same level of frost causes rotting of mature bulbs in autumn. I aim to cover plants with fleece on the evening before such a frost is forecast.
Likewise, seedlings of dill are more frost hardy than mature plants, whose stems may soften and rot after a freeze.
Although carrots and celeriac will survive some freezing, there are other reasons to harvest them before it turns too cold. Carrots may be eaten by slugs in the soil and rabbits above it, while celeriac may soften and rot because of Septoria disease, which can reach the bulbs via infected leaves.
