Since getting a greenhouse just over a year ago, I have been thinking throughout last year how to take most advantage of it. There must be a way of significantly extending the growing season living in south east England.
I have six small water barrels painted matt black which I will fill with water and place in the greenhouse. These will act as a thermal battery, absorbing solar energy during the day and releasing it at night to moderate the overnight temperature (assuming we stop getting well below average sunshine this winter). I have ordered a small replacement triangular pane to cover a broken one, and have ordered horticultural bubble wrap for insulation, which I will use to line the north side and the east/west sides of the greenhouse (not sure if the south side should be done as well yet). When the first early potatoes arrive I shall chit then plant some of them in one or two bags, placed between the water barrels next month. Around early February I shall top up one if the raised beds with compost and put some carrot seed tape down (Nantes). If we start getting near average sunshine and no more prolonged cold spells, I'm hoping I will get an early crop of carrots and potatoes in the spring.
Come the autumn, I will try sowing some brassicas in the greenhouse to overwinter and produce an early crop the following spring. The Real Seeds website says you can do this with one of their calabrese varieties. I may even try a second Christmas maturing crop of potatoes in bags as well.