Types of Greenhouses and Green House Gardening
Green House Gardening
A greenhouse enriches any garden. Besides colour in the greenhouse itself all the year round, it is also a source of colour for the house and the garden, since many of the brilliantly coloured flowering and foliage plants seen in the garden later in the year start life in the green house in winter, and those houseplants and pot plants which display such brilliant blooms in the lounge may be nourished in the greenhouse.
A small greenhouse may not be profitable for growing vegetables or fruit, but what could be tastier than your ownout of season and freshly picked? , and are other interesting greenhouse crops, and are becoming more popular.
The types ofavailable are wide and varied and so the type of greenhouse you choose depends largely on what you wish to use it for, and how much you are prepared to spend on it (both on buying it and running it).
The construction of a greenhouse is related to its use. The glass-to-ground-level types are suitable for growing tall plants planted in the greenhouse border itself such asor carnations. They are also good for plants which need maximum light at ground level, such as lettuces. If you want to use the greenhouse for pot plants, one with low wooden, concrete panelled or brick walls would be suitable. Some greenhouses combine glass-to-ground on one side with low walling on the other. The glass-to-ground-level types are more costly to heat, since glass loses heat in winter more rapidly than brick or wood, so for cold or exposed situations the low wall types are a better buy.
Conventional span-roof greenhouses are available in a variety of sizes. The most popular size is 8 x 10 feet. Larger and smaller ones are also easily obtainable. Modern-looking spherical, curved or hexagonal greenhouses have the advantages of trapping the greatest possible amount of light, but they must be well ventilated to prevent overheating on sunny days in summer. This usually means using a cooling fan.
Choose a greenhouse which has been well designed and which is built of tough materials. The modern aluminium alloy types of greenhouses are good, and high-quality galvanised steel will last a lifetime, but paint it regularly unless you are certain that it is completely resistant to rust. Oak is tough and there are designs which provide for sturdy internal bracing. Red cedar is also tough and very attractive and lasts well if treated to an occasional coat of preservative.
When choosing a greenhouse see whether it can be easily extended later on, whether it can be easily constructed and whether a putty or a no-putty system is used to fix the glass. Modern putties are much longer-lasting than the old-fashioned ones.
One of the most economical and convenient, and certainly the most space saving, is the lean-to, which can be sited against any wall except one facing north.
Before buying a greenhouse check with your local authority to see whether you need planning permission to build it. You probably will not, but you should check.
The site for your greenhouse should be as sheltered as possible without being overshadowed. If you erect the greenhouse with its length running from east to west it will get the benefit of most of the winter sun: if you give it a north-south alignment all parts will receive the maximum amount of summer sunlight. The east-west alignment is generally the best choice because you can alter plant positions in summer so that those needing most sunlight receive it.
Most greenhouse manufacturers supply comprehensive instructions on the erection of their greenhouses. They can usually be erected by unskilled labour. The first thing to make sure of is that the site is level. Low brick walls may be made with ordinary Fletton bricks, a 3 to 1 ratio of sand and Portland cement, and the skilful use of spirit level and measure. Follow the manufacturer’s glazing instructions carefully or you will have to contend with a leaking greenhouse. Plastic types of greenhouses are cheap, but are less efficient at trapping light and encourage condensation.
Heat your greenhouse according to your choice of plants. For instance, if you wish to grow stove-house plants and tender orchids you should remember as a rule of thumb that to heat the greenhouse to intermediate level (never below 50°F-10°C) costs twice as much as to heat it to cool house level (never below 45°F-7°C); and to heat it to warm house level (55°F – l3°C) costs three times as much, and to cool stove level (60°F – l6°C) four times as much as to heat it to cool house level. So if you wish to grow tropical plants you will probably plump for the heating system – solid fuel or oil – which gives you the cheapest running costs.
Another important aspect of modern green house gardening is automation, and it is here that electricity comes into its own. The list of gadgets includes-warming cables, propagators, overhead mist units which provide a moist spray for cuttings, electric fan heaters, electric tubular heaters or heating cables, fans and air extractors, and thermostats. In general, electric heating suits the man who has plenty of money but no time to spare, but it is also an economic proposition for the gardener who is interested in running a cool greenhouse.
The third main type of heater is the paraffin heater. A heater with a ‘blue-flame’ burner, which provides efficient use of the fuel, can hold its own; but only buy the type of heater made of non-corrosive metal. A paraffin heater is cheap to run and install, and the more expensive kinds have extension radiator pipes for heating larger areas. They are excellent for maintaining plants at a temperature just above freezing point. Oil heaters of this kind need careful attention and maintenance, both in respect of safety and efficient running. Such oil heaters and natural gas heaters increase the atmospheric content of carbon dioxide which plants require, and are sometimes favoured for this reason, though it is not certain whether or not plants can suffer from an excess of carbon dioxide in the air.
A really old type of greenhouse with 4 inch pipes for a solid fuel boiler can be converted to electricity by inserting an immersion heater in the pipes.
To find out how much heating your greenhouse requires you need to work out how much heat is lost and how much heat needs to be put in to overcome that loss and raise the heat to the required level. Quantities of heat are measured in terms of British Thermal Units per hour. Greenhouse manufacturers and greenhouse heating appliance makers will all help you work out the heating needs of your greenhouse. It is worth bearing in mind though, that an all-glass house invariably needs more heat put into it to maintain it at any given temperature than one that has brick or wood walls.
Greenhouse Ventilation and Shading
Having enclosed plants in a house to keep them warm it is also necessary to see that they get a change of air to supply them with carbon dioxide. Ventilation also ensures that the plants do not become subject to too humid an atmosphere. Undoubtedly the simplest method of greenhouse ventilation is to install an electric extractor fan, or fans, controlled by thermostat. On an automated system it is important to ensure a balance between heating and ventilation to avoid waste of power.
Shading is also important, and the cheapest method of shading a greenhouse is to paint the exterior of the glass with a proprietary lime solution mixture. When removed in winter the glass gets a cleaning which helps to increase the amount of sunlight entering the greenhouse at that time. Unheated greenhouses often become overheated in summer, and need shading to avoid scorching the plants.
Automatic Greenhouse Watering
Capillary watering is one of the most important advances in greenhouse gardening. It works on the simple principle of allowing plants to draw up water from a layer of fine sand. It is only suitable for watering pot plants (preferably in plastic pots) and is installed on the staging at the side of the greenhouse. The staging must be level and a perfectly flat greenhouse bench covered with polythene is better adapted than the slatted wood staging commonly used for greenhouses. A two inch thick layer of fine sand is fed with water by a pipe covered with glass fibre, running through the sand, and linked to a level-water ball valve system.
Lighting in the greenhouse is essential in winter for those out at work all day, and it is possible to obtain suitable fluorescent tubes which provide near ‘natural’ colour. More elaborate greenhouse lighting will enable you to flower, carnations and other plants out of season, and to promote rapid growth.