Winter Salads Under Cover in Scotland: What to Sow, When, and What Survives

The sowing window for winter salads is narrow. Between mid-August and the end of September you can put in corn salad, claytonia, land cress, mizuna, mustards and rocket and have leaves to pick through the winter. By October the light is falling fast, the first frosts are close on high ground, and seed sown then mostly sits as small seedlings until spring.

Jump to sowing windows by region. Already past your window? See what to do after the cut-off.

What closes the window

Falling light and cooling soil end the sowing season for most gardens. On high ground, frost gets there first.

Light goes first

Salad leaves sown in September need to reach picking size before the days shorten to the point where growth stops. Plants still tiny at the start of November will mostly hold rather than grow. Cooling soil makes late seed slower to germinateA seed sprouting: breaking dormancy and putting out its first root and shoot, given the right warmth and moisture. Full definition → and easier prey for slugs. Under cover you keep the frost off but add no light at all, and a dirty or condensation-covered skin takes some of what there is. The day length and photoperiod article covers the mechanism, and the Shetland and Orkney winter darkness article shows how extreme it gets in the far north.

Frost matters least in the lowlands and most on high ground

Lowland Scotland sees little air frost before late October, and cover deals with most of what it gets. On high ground the order flips. An air frost is a day when the air temperature falls below freezing. Braemar averages more than five of them in October alone, and its first arrive in mid-to-late September, before a September-sown salad has made a picking. Sheltered hollows inland frost earlier than the surrounding slopes, so a frost pocket in a low-lying garden brings the date forward.

Figures are 1991-2020 averages, and the frost band is worked out from monthly counts, so allow a fortnight either way. Braemar is deep into frost while Stornoway is still barely touched, which is why a single "Scottish sowing date" does not exist. Look up your own area on the Scotland frost dates page or try the frost date calculator.

Light is the real limit

In lowland gardens, cold hardiness is rarely what decides whether a winter salad survives under cover. Corn salad, claytonia and land cress are hardy to well below what a covered lowland bed will see (land cress carries the RHS H7The RHS's H1a–H7 scale for how much cold a plant can survive outdoors, H1a being tender indoor-only and H7 hardy anywhere in the UK. Full definition → rating, hardy below -20°C). What catches growers out is that below a certain amount of light the plants stop making new leaf. On higher ground and in glens, hard frost adds a second problem, dealt with under cover choice below.

Sunshine hours are not the same as daylight, but they track how much usable light reaches the bed. Monthly averages for five Met Office stations:

Mean monthly sunshine hours, 1991-2020.

December is the bottom everywhere. Edinburgh and Aberdeen get about twice as much sun in October as in December; Inverness and Stornoway get about three times as much, and Lerwick close to four. At Lerwick, December offers 20 hours of sun across the whole month, well under an hour a day, before glass or polythene takes its share. The west and the islands start from a lower October figure, so their window for banking growth is shorter than the frost table alone suggests.

Anything sown in autumn is racing to reach picking size by early November, and everything after that lives off the reserve. From about November to January, expect near-stall: leaves hold their size, you can pick them, and very little replaces what you take. Growth picks up again from February, when the hours climb steeply. Supplementary lighting can shift this, and the LED grow lights article covers whether it is worth it for a salad bed.

Which leaves are worth sowing

If you only sow three things, sow corn salad, claytonia and land cress: they are the hardiest of the group.

A cloche is a small glass or plastic cover over a plant or short row; a low tunnel is a hooped row cover of polythene or mesh; fleece is a woven fabric draped over the crop or laid on hoops. Mizuna and mibuna are mild oriental salad leaves, and komatsuna is a mustard-spinach type.

Lettuce is the riskiest leaf here. A dense heart traps moisture and can rot from the centre in still, damp air, so treat winter lettuce, 'Winter Density' included, as a leaf crop and pick outer leaves young rather than waiting for a firm heart in December. Hardy spinach is the other worthwhile addition: sown from late summer to early autumn, it crops in autumn or early spring under cloches or fleece from October.

When to sow, by region

Winter salad sowings run from August to September, with rocket and lettuce stretching that a little. Scotland's regions sit at different points inside that window. Treat the dates below as starting windows and adjust them for your own bed.

These windows are our own reading of the frost and sunshine tables above, not a published Scottish schedule.

Shetland and Orkney get about six hours of daylight at midwinter, and the recovery of light after the solstice is the real sowing cue there. The darkness article sets out how to work with that.

The northern and upland windows open earlier because light and warmth fade earlier there, and cooler summers make early sowing less risky. Hot, dry spells are what push rocket and oriental leaves to bolt, so in a warm lowland garden hold their sowing until mid-to-late August.

On high ground, lowland advice is the wrong reference point. Sow earlier, use a frame or tunnel from day one, and accept a shorter harvest season. In a glen or beside a tall hedge, low winter sun may never reach the bed, so site it where it gets the most of what there is. The planting calendar tool turns these windows into dates for your postcode. Starting seed in modulesA tray divided into small individual cells, each sown with its own seed or seedling, so each plant grows undisturbed roots until it's ready to plant out. Full definition → in late July or August and planting out is another way to get ahead of the light.

Which cover to use

The cover matters less than the leaf and the sowing date, but it changes what you can pick in January. Cloches and fleece add roughly 2°C, which helps at the edges of the season but is not a great deal on a hard clear night. In the uplands and glens, tender leaves such as rocket, mizuna and lettuce may need fleece laid over the bed inside the tunnel.

For tunnel versus glass, see polytunnel vs greenhouse; planning rules for a tunnel are in the polytunnel planning permission article; frost-night tactics are in protecting plants from frost.

In exposed gardens, wind is often what ends a cover before frost does. A cloche that lifts in the first November gale takes the crop with it, and a loose polytunnel skin will flog until it splits. Anchor everything, set the tunnel end-on to the direction your worst gales come from, and check any cover on an exposed site after every big blow. The wind-securing article has the detail. In the uplands, where snow lies longest, brush wet snow off hoops before it builds up.

What fails and why

The light stall

A November sowing for a December crop does not work. Seed may germinate, but there is not enough light to power growth, and the seedlings sit there being eaten by slugs. A late sowing is the classic winter-salad disappointment, and it is a light problem, not a cold one.

Damp, mould and botrytis

Grey mould thrives in humid, overcrowded conditions under glass and covers. Its spores germinate when leaves stay wet for a long time or relative humidity stays around 90 percent or higher, and it typically enters through dead or damaged leaf tissue before spreading to healthy leaves. In a Scottish tunnel that means a still, wet week in November. Ventilate on every dry day, even when it is cold, space plants so air moves through them, water the soil not the leaves, and remove yellowing leaves as you spot them. Bagging the removed leaves stops the spores drifting.

Slugs

Slugs stay active through mild, damp winter spells, and the west coast and islands, where November frosts are rare (Stornoway averages 1.4 days), have plenty of them. They feed at night on soft leaves and seedlings. Sturdy plantlets grown on in pots stand up better than fresh seedlings, watering in the morning rather than the evening helps, and clearing debris removes hiding places. Copper tape, bark, eggshells, grit and wool pellets showed no reduction in slug damage in realistic garden conditions. Encouraging predators such as birds, frogs, toads, hedgehogs and ground beetles, and a nematode drench, are the approaches that hold up. The slug deterrents article sets out the rest.

Waterlogging

Plants can freeze if they stand in pools of icy water, and lettuce plugs sitting in a wet bed rot. Plant winter lettuce plugs on the bed surface rather than sunk in, and use free-drainingSoil that lets water pass through quickly rather than pooling, so roots aren't sitting in wet ground after rain. Full definition → soil or a raised bed. Over winter the soil under cover needs far less water than in summer, and overwatering is a common killer of winter salad.

Flea beetle

BrassicaThe cabbage family: cabbage, kale, broccoli, cauliflower, Brussels sprouts, kohlrabi, swede, turnip and more, sharing the same pests, diseases and rotation rules. Full definition → leaves, including land cress, mizuna and rocket, can end up shot with small holes. The damage is cosmetic and insect-proof mesh prevents it.

Realistic picking

Winter salad growing is not a cut-and-come-again bonanza. Pick a few outer leaves from each plant and leave the growing point alone; snipping about 2.5cm from the base is the standard cut. Pick little and often, and pick on dry days, since cut, wet leaves invite rot.

By December the regrowth flush of October is gone. Take a handful, not a bowlful, and never strip a plant, because it has no reserves to refill from. The salad you eat in midwinter is mostly growth banked in October.

The February restart

Once the light is climbing, clear dead leaves and mouldy patches, loosen the surface, and top up the plants that survived. Sow fresh corn salad, land cress and mizuna in trays or under cover as soon as the light allows, following the planting calendar for your area. These sowings crop from early spring and are usually worth more than a hopeful late-October sowing that has to sit through the dark months. Overwintered plants will run to flower in spring, so treat them as a bridge to the new sowings, not a permanent crop.

What not to bother sowing after the cut-off

If you miss the window, do not sow rocket, oriental leaves or lettuce after early October in the Central Belt, or after late September further north. They will germinate and then stall, becoming slug food. Corn salad has the best chance from a slightly later sowing, though it will give little until spring.

The better plan for a missed window is to buy plug plants (small ready-grown seedlings) of hardy lettuce or leaves and plant them into the tunnel. Plugs planted in early to mid-October are well ahead of anything seed-sown then. Otherwise, save your seed and start again in February.

Common questions

Sources