Early January and you can grow shorthorn carrots in a frame with thermostatically controlled soil warming cables. Seeds planted directly into the soil in the frame will give a supply of tender young roots in early spring.
Onion seed sown in John Innes seed compost in seed trays placed in a heated greenhouse with an average temperature of 13ºC (55ºF) will provide seedlings for transfer to open ground in spring. Early peaches can be grown in the same conditions.
Mid January you can be sowing small salads under glass in a slightly heated greenhouse or heated frame. Grow mustard and cress, lettuces and radishes. Plant potatoes in frames and pots in John Innes potting compost No.2.
Late January and it’s time for forcing rhubarb and seakale outdoors. In the greenhouse sow French beans for forcing, leeks and even early crop tomatoes.