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Greenhouse Irrigation

By: Dr Gareth Evans - Updated: 26 Sep 2012 | comments*Discuss
Evaporation Drying Watering-cans Hoses

Plants depend on water and within the greenhouse with no rainfall to supply it naturally and the added warmth to make the soil dry out more quickly; some form of artificial watering or irrigation system inevitably becomes essential.

Traditional watering-cans are, of course, the simplest solution to the problem. They are particularly useful in providing very specific, targeted watering for individual plants, particularly if they are being grown in pots or containers. However, as a means of achieving mass watering, they are far too labour-intensive to be practical for anything other than the smallest of greenhouses.

Many gardeners are inclined to try to overcome the limitations of the watering can by using a hosepipe instead, but this approach itself has its problems – chiefly in terms of achieving the delivery of water where it is really needed, rather than on the leaves and soil surface.

Automated Watering

Watering a large number of plants in a well-stocked greenhouse can be a major task, especially if it is to be done by hand. However, there are alternative approaches available, including seep hoses, drip irrigation, misters and sprinkler systems, which make the job much easier.

Many of these systems can be automated to varying degrees, using modern timers or controllers, which range from the cheap and simple to the very sophisticated – with a price tag to match!

Water timers, for instance, fit between the irrigation hose and the tap and can be set to allow watering to take place at specific times of the day and for a given period, allowing you to water at night to avoid evaporation, for example, without having to be there yourself. These relatively simple devices are also invaluable if you are out all day or when you go away, keeping the soil nicely moist in your absence. More complex water controllers can take the automation even further, measuring soil moisture and watering accordingly to keep the growing conditions at their optimum.

Picking the System

Seep hoses are full of thousands of small perforations which allow water to slowly leak out along the length of the hose. Buried two or three inches below the soil, they deliver water steadily and very efficiently to the plants, with very little being lost to evaporation and without the higher risk of mildew or mould which over-wetting the leaves can bring. This system also encourages good root formation, the roots developing downwards rather than sideways in their search for water, making the plant sit more firmly and securely in the soil. Drip irrigation systems work on a similar idea, but lie on the surface of the soil, the water seeping out of small drip heads and directly into the soil which in some ways is a more natural way for water to be delivered.

If large numbers of seeds or cuttings require watering, misters may well be the best option to consider – filling the greenhouse with a fine spray of water which gradually moistens the soil without disturbing it. Overhead sprinkler systems are also commonly used in greenhouses – especially larger ones – and can successfully cope with the demands of mass watering, though like misters, adjusting the delivery to match the needs of individual plants is not easy to achieve. In addition, since these methods can both lead to water sitting on the foliage, it is important to keep a careful look-out for the first signs of mould or mildews.

Like so much in the greenhouse, selecting the right irrigation system very largely depends on the type of plants being grown and the scale of the whole thing. While a long-spouted watering-can may be all the irrigation system you need to grow a few tomatoes in a small unheated greenhouse, things are a little different if your passion extends to propagating bromeliads and strelitzia plants under true “hot-house” conditions. Although much of the decision often comes down to personal preference or the recommendations of other growers, it is certainly worth putting in the effort to get the irrigation right – after all, few things are more fundamental to growing plants than water!

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