Sowing under a cold frame in October-November: what still goes in

Late October, you might think sowing season is over. Not quite: under a cold frame, a cloche or a tunnel, a few species still accept being sown or transplanted — and above all, everything already under cover needs precise care to get through winter. Here is what can still be done in October-November, and how to run a cold frame until spring.

What you can still sow in October-November

Let's be honest about the calendar: most winter sowings happen in August-September. But under cover, the window stays open for a few species.

And for winter lettuces already sown in August-September: transplanting is still possible until the first real cold — 4-5-leaf plants, bare-rooted, "floating" transplants with the heart above soil level. Under a frame, plant tighter than outdoors: the harvest can double.

The frame: dimensions and exposure that matter

The classic box is 20 cm high at the front, 30 cm at the back — the slope catches the rays and sheds water. The professional version: 3.90 × 1.30 m for three lights; for amateurs, combined plastic box-frames of 1 × 1 m, half-opening, do the job. Site it in the most sheltered spot in the garden, against a hedge or wall, opening south or south-west.

Three upgrades that change everything: the "hotbed collar" — a belt of straw the full height of the box and 30 cm wide, topped with mats at night; wall insulation with polystyrene if your frame is glass-and-aluminium (markedly colder than brick); and shading for glazed frames — a slatted screen, jute cloth or mats — because winter sun on a closed light overheats as fast as frost bites at night.

The hotbed: engine of the winter frame

For real forcing, tradition relies on the manure bed: a 40 cm mattress of fermenting strawy horse manure (built in three trodden 30 cm layers), covered with 10-15 cm of soil. As it breaks down it fires the "heat flush" — up to 85 °C for 5-6 days, pasteurising the substrate and killing weed seeds — then settles around 20 °C. Sow only when the bed thermometer falls back to 20-22 °C. If the bed "smokes" too hard in the first days, water abundantly; a third of dead leaves in the manure tempers the peaks.

The mild or "sour" bed (30-60 cm of manure buried under 30 cm of soil, ~10 °C) is enough for simple protection. And for the better equipped: a thermostatic cable buried in 20 cm of sand turns the box into a mini-greenhouse (+8 to +10 °C) — but fixes it in place.

Winter management: ventilation is non-negotiable

Mistake n°1: a frame kept shut on a fine winter's day rots the salads. The rule is simple:

• Open on fine days, on the side away from the wind, with a 3-notch ratchet to meter the gap.
• Close before sundown to keep the day's stored warmth.
• Icy nights (-3/-4 °C): cover frames and boxes with mats, an old carpet or a warm cloth — set before the temperature drops, removed in the morning unless the day stays bitter.
• Condensation: wipe the light daily; remove pane or plastic bag as soon as germination shows, or fungal diseases strike.
• Watering: in the morning, with room-temperature water — 10 litres per 2 m² through a fine rose. In tunnels, double the side walls with bubble wrap in winter.
• Never insulate the top permanently: plants need light as much as warmth.

Mistakes that kill a winter frame

• Leaving condensation on the glass after germination.
• Watering to mud — seeds lack air and rot.
• Sprinkling over an open frame: droplets on foliage cause scorch spots.
• Sowing too dense: thinning becomes destructive.
• Assuming a tunnel needs no watching: its ground fastening is delicate and the wind tests it.
• Forgetting hardening-off: before spring transplanting, open progressively during the best hours.

A winter frame is a living tool: it opens, closes, gets covered and aired every day. Well run, it gives you salads into spring and early plants for March — the logical next read: protecting the whole garden from the cold, then winter mulching by material.

Also read: winter indoor sowing for what can't stay outside even under cover.