Alternatives to greenhouses
Polythene tunnels (Polytunnels)
A large polytunnel can be a real bonus for your school garden. They consist of polythene film pulled tightly over a curved metal structure to provide a cost effective protected environment. They are however inefficient to heat, and should not be used for overwintering frost-tender plants. They are good for growing summer crops like tomatoes, cucumbers, melons and squashes and for raising salad crops earlier in the year. They are best installed by a professional because it can be particularly difficult to get the skin tight across the framework. If you can afford it, a poly tunnel with straight sides improves working conditions by providing more headroom and allowing more ventilation. Straight-sided poly tunnels often have a mesh that allows air in. They are adjusted by winding a sheet of polythene up and down over the mesh.
These are smaller box-like structures made of wood, metal, brick or glass. They have a sloping, hinged lid glazed with glass or plastic.They are cheap to make and are useful for hardening off seedlings in the spring. They are also useful for growing on hardwood cuttings during the winter months. Consider carefully where you site cold frames. A south facing postion and away from areas of high foot traffic is best.
These are structures that are placed directly over the plants growing in-situ. Plastic drinks bottles with the bottoms cut off are also useful. It is important to add a few extra ventilation holes to allow some air to circulate around the growing plant. They also provide some degree of protection from garden pests such as slugs and snails. Other examples include bell cloches and sheet-cloches that are placed directly over the plants as they grow.