Life & Work

The benefits of growing plants in a greenhouse


Small homemade greenhouse made from galvanised piping. Photo/Courtesy

Investing in a greenhouse is ideal in order to protect plants from extreme weather conditions. One can either build one or invest in a ready-made one.

A small greenhouse or shadehouse in the garden is very useful to have, especially if you want to grow plants that need the extra protection from the sun, wind and rain or if you are just looking to increase the daily temperatures and humidity for the plants.

If you live in the cooler climates, above 2,000 metres altitude, there is even more need for a greenhouse. Rain, not that we ever have much of it nowadays, would cause a problem when rooting cuttings of succulents, so they would be better protected in a greenhouse.

We see more small scale farmers today are using greenhouses in which they can provide better protection for growing their crops of tomatoes, courgettes and some cut flowers.

Where Best to Site the Greenhouse?

Level ground in a sunny position would be ideal. In a greenhouse it is easy to control shade, but in a shady location it is very difficult to increase the amount of light. A location where there is dappled light for part of the day would be alright but avoid deep shade under trees.

Gently sloping ground would be alright but steeply sloping ground would need the roof and the floor inside the greenhouse to be stepped, which just adds problems.

Also consider the direction of the prevailing wind so that the roof structures openings face away from the wind to give good ventilation and avoids the rain beating in during times of a downpour.

Pros and Cons of a Do-it-Yourself Timber Greenhouse against Bought Steel Greenhouse

Basically this is the difference of a greenhouse built using timber or buying a steel greenhouse from one of several vendors now operating in the country, whose main business is the commercial horticultural industry.

A timber greenhouse is relatively easy to make using timber, nails and a saw but it is very important that the timber is properly tanalised (cellcured) from plantation grown timber and not from forest cut timber.

Tanalised timber keeps the termites away and slows rotting of the poles that have their feet in the ground.

The structural members of steel greenhouses are galvanised and are therefore much longer lasting than timber. These structures are not so simple to erect unless the decision is to go for what is called a “Polytunnel”.

These tunnels are made from bent steel tubing forming an arch and can now be purchased locally in various sizes and come with either closed or open ends of various designs.

There are also various designs of steel greenhouse available on the local market. Steel greenhouses are much more expensive than timber but of course they last very much longer.

The cover for both types of greenhouse is UV treated polythene sheeting. The UV treatment is important to lengthen the life of the sheeting as here on the equator the intensity is quite high especially at the higher altitudes.

In order to make the polythene last, heat build-up in the supporting roof members must be kept to a minimum. The simplest way to achieve this is by painting the top of all timber or steel to which the polythene will be attached with brilliant white acrylic paint.

Also paint a strip on the outside of the polythene anywhere it touches a structural member.

Polythene has a large expansion coefficient, and a high diurnal temperature variation will cause it to stretch and shrink.

Polythene should be fixed at the hottest time of day, stretching it as tightly as possible. It will contract (shrink) as the day cools. At night it will become like a board, and during the day it will be stiff enough to prevent too much flapping. 


Maintenance will chiefly involve replacing the roof cover and keeping white ants away from any timber posts.

Remove the old polythene when it has become brittle and unsightly. Disposing of old polythene is always a problem as burning is not recommended for environmental reasons and the harmful vapour.

It is possible that it can be sold for recycling if the quantities are large enough. If the old polythene has to be burnt then an incinerator should be used as it will then burn at much higher temperatures and lessen the harmful pollutants.

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