Roof gardens are known to make use of valuable growing space in urban areas and can be very productive. I'm using the roof of our duck house to over-winter some hardy plants that were raised from cuttings and seed in late summer and early autumn.These plants are all grown for their flowers, various dianthus, sweet peas, and other hardy annuals, but the principle could also work for hardy food plants.
I've always liked starting the growing season in autumn because a strong healthy September started plant can be planted out in spring when seeds are struggling to germinate. It's nice if you can sow seeds in situ, in autumn, but it's rare that I have a bed that is either empty or prepared for seed. By starting in seed trays and pots you can make the most of the last of the natural warmth for germination. Because the plants barely grow over winter, (with most of the energy going into strong root systems,) you can keep them in small modules or pots. In the past I've always looked for sheltered places to overwinter plants but when our Muscovy ducks, Jack and Vera, joined the family my son made them a strong safe house. The plants absorb excess rainfall and provide a thick layer of insulation for the ducks. At the same time the plants may benefit from the animal heat below. The sloping roof ensures the best drainage and I've always found that cold and wet combined, are much greater enemies of over-wintering plants than cold alone.
The height of the duck house roof means the plants are out of the way of many pests, particularly slugs, that would find them much more easily at ground level. Up on the roof there is a lot more sunshine too. In December and January, when the sun is at its lowest in the sky, the plants were still getting three or four hours of sunshine on good days. The picture was taken in early February at 8am. While the rest of the garden was in full shade this growing area was in full sun. Over-wintering plants grow very little but these ones at least won't be weak and leggy from pulling to the light.
I would only suggest this for hardy plants, and would recommend attention to the winds they might be exposed to, but despite being frozen solid many times, soaked severely and under a blanket of snow I haven't lost a single one. When these are planted out in the garden in Spring the roof will be clear for more seed trays which I can cover with lids and some horticultural fleece overnight. All I have to worry about then is hungry ducks, or more happily, ducklings.
Wendy Ogden writes a blog called On The Edge, all about writing, gardening, scenery and living by the sea.