What to Grow from Seed in the Greenhouse Over Winter

The winter months, December, January and February, aren't very productive in the garden but your greenhouse, even unheated, can be used to grow a number of plants ready for an early start when spring arrives.

Things will grow very slowly if at all in December and January. Not so much because of the temperature but because the length of the day is at its shortest around the winter solstice (21st December). They will be gathering their energies ready to leap ahead come February when the days noticeably lengthen so long as the greenhouse is at least frost free.

Potatoes

Early potatoes planted in large buckets or thick plastic sacks can be started in January to give a crop in March and a second sowing in February can be moved outside to provide a crop at the end of April.

Broad Beans

Starting off broad beans in 7.5 cm pots ready to plant out in the ground as soon as the weather allows. In southern areas you can start off in early January but it is probably best to wait until February in the colder northern areas of the country.

Brussels Sprouts, Cabbages and Cauliflowers

Sprouts and the summer brassicas can be started in late winter in the greenhouse and brought on until March when you can move them up a pot size and harden them off in a coldframe to plant out as soon as the weather allows.

Garlic

Spring garlic can be started in 7.5 cm pots in January to plant out in March.

Spring Onions

The winter hardy variant of White Lisbon can be grown in deep trays or shallow troughs in the greenhouse. It can be grown outside but the milder conditions in a cool greenhouse will really encourage growth.

Shallots

Shallots sets can be started in 7.5 cm or 10 cm pots and planted out in the Spring when they'll be well ahead of outdoor planted cousins. Varieties started from seed will do well in the greenhouse.

Bulb Onions

Bulb onions from seed will do well started in January. If it's really cold, use a propagator to germinate and then harden the seedlings off to the greenhouse.

Early Peas

Early peas can be started in late winter for a very early planting. One popular method is to fill a length of old guttering with compost and sow into that. When spring arrives, draw a trench outside and slide the peas into the trench.

Leeks

Leeks can be started in January. Take a display trough, mine is about 1 metre by 20 cm by 30 cm deep, fill with compost and sow directly but thinly. An old saying is to treat every seed as if it cost a pound when sowing.

Once the seedlings have reach pencil thickness they can be planted into dibbed holes to produce a blanched leek.

Carrots

Early Nantes and Amsterdam Forcing early varieties will do well from a late winter planting.

Salads

It's well worth sowing a pot of mixed winter salad leaves each week to provide a successional crop – often you'll get away with three cuts before the pot is exhausted

In conclusion, don't just think of your greenhouse as a place to grow summer crops like tomatoes and cucumbers. It can be helpful and productive right the way through the year.

Copyright © John Harrison 2015