A greenhouse uses sunlight to warm up trapped air inside it. This raised temperature is useful if we want to grow summer crops during colder months or if we are in a cooler part of the country and want to ensure a good harvest of sun-loving crops like capsicums, tomatoes and grapes. A small greenhouse can provide perfect conditions for growing crops under controlled conditions at times of the year and in parts of the country where they might otherwise not survive at all outdoors. They offer warmth and shelter from strong winds and torrential rain. There is an initial investment in a greenhouse, they don’t come cheap, but soon enough you should start saving on produce bills.
Greenhouses come in a wide variety of shapes and sizes and some are more permanent than others. Size-wise, a small aluminium-framed, walk in greenhouse – about 2 metres wide and around 4 metres long with planting areas along both sides should suit most domestic gardeners. You can get smaller and larger, the size depends on whether you only want a greenhouse to raise seedlings for planting out in the garden during summer or whether you need space to grow crops such as capsicums, tomatoes, beans, cucumbers and the like in sufficient quantities to feed numbers of people. You can make your own greenhouse with timber framing and polythene sheeting or recycled sheets of Perspex. Another option is to create a cheap version of a greenhouse and erect a polytunnel with polythene sheeting stretched over large metal hoops.
Plants in greenhouses need regular attention - moisture has to be regularly provided by hand using a hose or watering can or automatically with an irrigation system. Temperature is controlled by ventilation with open/close panes of glass in the roof and sliding doors. Light levels are regulated with shade cloth when the days are long and hot and the use of a grow light when days are short and dark.
A greenhouse should ideally be located in a sunny spot to take advantage of available light. Avoid placing one beneath large trees where branches may fall and damage glass panes. Overhanging foliage can also cause glass panes or polythene to quickly become dirty and this can be hard to clean. If a greenhouse strikes you as a complete necessity but a bit of an eyesore then place yours amongst your plants and plant beans, sunflowers, globe artichokes and Jerusalem artichokes alongside it to help it merge with your garden. Greenhouses can be attractive and elaborately designed. They can be part plant house and somewhere to escape to with the radio or a seed catalogue on rainy winter days.