If an all-glass house has been purchased it is as well to line the lower part during the period when in use as a propagating house, using either sheets of polythene film or roofing felt, to help maintain a more effective temperature control.

The greenhouse should be as large as the pocket and the amount of available space will allow because, strange as it may seem, large greenhouses are much easier to handle than small, for a variety of reasons. In the main a small house will be far more subject to wide temperature variations, heating up rapidly when the sun is out and cooling rapidly at night. It is much more difficult to maintain that indefinable rightness for growing that the gardener, for want of a better term, calls “a buoyant atmosphere” and the problem of heating is rather greater.

Usually a water circulating heating system will give too much heat for a small house, while most alternative systems are either expensive or somewhat unsatisfactory in one way or another.

Whatever the size there should be ventilators on either side of the roof so that air may be given without too much draught whichever way the wind is.

Whether the greenhouse is big or small, when buying a new house, remember that it is better to have a wide house than a long house, as the extra width makes it much easier to handle the plants on the benches.

To a dahlia grower, unless, of course, lie merely propagates by division, a greenhouse without some method of heating is almost useless, except perhaps during May, when it can he used for hardening off bought plants. The best, and the cheapest in running costs comparatively speaking, is the traditional boiler and pipes. Preferably these would be 4 in. pipes and should extend round three sides of the greenhouse, below bench level, to give bottom heat. As the installation costs are rather high, and, in a very small house, this form of heating tends to be rather fierce, many growers use some other form of heating.

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