The conventional greenhouse shape with vertical sides and gabled roof should not be dismissed just for the sake of being different and modern. For many years it has been found satisfactory and it uses space to its best advantage. The pitch of the roof leads condensation to one side and sheds rain well. It will be noticed that some greenhouses have the sides sloping at an angle-called the Dutch light design.
Such structures could be made up from standard frames or Dutch lights also used for protecting low-growing flowers and vegetables, but the advantage of a side with a slight slope is that there is less glass thickness for the suns rays to travel through. However clear a glass may appear to be to the eye, some light is always absorbed. This can make a slight difference to some crops, but mostly it is of concern to the commercial grower interested in early produce.
However, a greenhouse with an excessive side slope can be undesirable for the home garden. It may be difficult to work close to the sides and is certainly not advisable if you want much staging. Some greenhouses are given a slightly circular slope to the roof and sides by placing panes at suitable angles. These designs also permit maximum light. Fortunately they are also designed to be practical in the home garden in most cases, and they can generally be equipped with the usual staging if desired.
In recent years several designs have appeared that have obviously been made for appearance or novelty rather than any serious growing. A bad fault is a roof that is too flat. This often leads to condensation drip which can be a nuisance in the conservatory or home extension type of structure; and it can cause constantly moist conditions at the roots of plants in winter, possibly causing them to rot.
There are a number of circular or hexagonal greenhouses available. This shape is not really new, and was popular in Victorian times for ornamental conservatories. A round house can look very attractive as a garden feature and when filled with decorative plants, It does not use space so well, and if you are looking for a practical design for general-purpose growing it would be advisable to choose the more conventional square or rectangle. A useful design is that which combines glass to ground one side with a dwarf wall or boarded base the other.
Another practical design is the combination greenhouse which has a shed attached. The shed may be alongside so that the greenhouse forms a lean-to, or it may be at one end. The shed can be used for potting and / or the storage of the usual garden tools. It should of course make an ideal potting compartment.
It is best if the greenhouse can be entered from the shed, rather than the shed entered from the greenhouse. This means less opening of doors in winter to let cold air into the greenhouse section. The lean-to type of shed / greenhouse should have the glass facing south if possible when sited.
Also of recent appearance are mini-greenhouses. These are little more than plant cases generally mounted on legs for convenience. They are best used for choice plants of the decorative kind, although they can make useful propagators and they can be sited inside the greenhouse too. A plant case or mini-greenhouse inside can be heated to a high temperature economically, so that tropical plants can be grown in them-provided slow growing or small subjects are selected. Small orchids, and plants like African violets do very well in heated plant cases. A modern plant case of recent design is a tall structure mounted on castors.
It can be opened up rather like a screen to give easy access to the plants displayed on shelves. It is called by the makers the flower tower.
Compartments and extensions
Attention has already been drawn to the fact that it is important to give plants the environment they prefer with respect to temperature, humidity, ventilation and so on. So that this . can be done for a wider range of plants under the same roof, it is most useful to have the greenhouse divided by partitions one or more with communicating doors. For example, a greenhouse divided into two compartments could have the first section at the door end devoted to plants needing little warmth or none at all, with the section at the far end used for more tender subjects. Similarly, one section can be well ventilated if necessary with the other maintained at a high humidity for those plants that like it. If you want several sections at different temperatures, the centre section or sections should be kept at the highest temperatures and the outer sections lowest. This way heating is more economical because losses are reduced. It is far better and more convenient than having several separate greenhouses.
Most makers now provide designs that have provision for the addition of partitions which can be easily fitted at any time. If an extension is made to a greenhouse it may be worth considering adding it as an extra compartment.
It is a common mistake for beginners to start off with a greenhouse that is rather small. Before long it is bursting at the sides with plants-and overcrowding often leads to trouble and disappointment, It is consequently wise to buy a greenhouse that can be extended, if and when the need arises, and to leave enough space for an extension when erecting the house.