A glasshouse, no matter how simple in construction, can have a dramatic effect on a cold climate gardener's life. There is a considerable saving in money for anyone who is able to raise a few punnets of bedding plants, early seedlings or extend the growing season.
Igloos, which are basically a framework of either metal or plastic piping covered with a thick polythene roof are used extensively in the nursery trade as a cheap and effective way of providing reasonably well controlled growing conditions.
PVC and fiberglass have become popular greenhouse materials over the years, though it has to be admitted that PVC is less durable for it gradually becomes brittle and will crack within three to four years.
Where there is limited space for a poly tunnel, a cold frame will only require a few metres of ground.
The modern cold frame is in fact several centuries old. Records show that the Romans used frames glazed with a thin sheet of mica or transparent stone under which they nurtured early food crops, potted plants and vines.
A cold frame is actually a contradiction in terms. While it is not heated artificially from the base it is warmed by the rays of the sun. Roman frames were placed over pits of rotting dung which generated considerable heat. Years later gardeners are using the same principles, employing naturally fermenting materials such as stable manure and autumn foliage.
A barrowful of each forked together should be carefully and firmly trodden down, for if there is any looseness in the pile there will be a surge of heat followed by a rapid cooling which would defeat its purpose. Once the bed has been built up to a depth of about 45cm the frame can be placed on top. The final layer within should be 15cm of firmly packed sandy loam.
After four or five days the initial heat should have leveled off, leaving the bed with an even temperature, which will remain so for some time. On top of that, plants will continue to take root or grow on.
A few other strategies can be used to protect from frost damage. Move potted plants close to a warm wall, then cover with a layer of frost cloth suspended over a frame of wooden stakes.
Create cloches from half a plastic soft drink bottle. Keep the soil moist - better able to absorb and store heat during the day. Spray foliage with 'Droughtshield' throughout winter to form a protective, flexible film over the leaves. Don't prune off any damaged foliage until all risk of frost has passed.
'Brassica' is the name given to a family of winter greens, which includes cabbage, kale, broccoli, cauliflower and so on. Unfortunately, all of them are popular with caterpillars, aphids, and cabbage white butterflies. Dipel, based on naturally occurring bacteria, is highly recommended for effective control