The best method of watering a mixed collection of plants in a small greenhouse is the traditional watering can. It might be time-consuming using one but it allows you to monitor the flow and ensures that all the plants are watered according to their individual needs. A useful addition to a greenhouse is an automatic watering system, especially in the summer or when the greenhouse is left unattended on a regular basis, since some pot plants may need to be watered several times a day in very hot weather.
Most often used in a greenhouse is a watering system that relies on capillary action to draw up water. Pots with plants are placed on a 2-5 cm layer of clean sand that is placed on the greenhouse staging and permanently wet. To protect the wood staging line it with sheets of heavy-duty plastic or place the sand in aluminum or plastic trays. Add a length of plastic gutter to the edge of the bench and keep it filled with water.
A lighter and easier to keep clean, but just as effective as sand, is the capillary matting. It is widely available in rolls and can be cut to the required size very easily. To keep the capillary matting continuously moist just trail the edge into a water trough or any reservoir, making sure is kept topped up with water.
To make sure this system is effective you must verify that there is enough contact between the compost in the pots and the source of moisture so that the water is continuously supplied to the plants root systems. Plastic pots usually allow good contact while clay pots may require a wick. This is a cut out of a piece of spare capillary matting and placed in the drainage hole of the pot.
During winter months do not use capillary systems in the greenhouse because most of the plants are dormant or grow very slow during this period and they only need a very small amount of water.
Widely used in commercial greenhouses is a system of overhead pipes with nozzles from which water is sprayed onto the plants below. This system is ideal for watering a large number of plants that are all at a similar growing stage. It is not suitable for small greenhouses that contain a wide variety of plants at different growing stages and with different watering requirements. This system is also expensive to be installed and create too humid atmosphere if used in winter.
These are widely used in the garden and inside the greenhouse to water border crops or to keep capillary matting moist. This system is not very efficient in very hot weather as it may not supply enough flow of water to the plants.
Trickle irrigation systems
This type of irrigation system consists of a series of small-bore tubes, each with an adjustable nozzle. The tubes are placed in the individual pots or growing bag or near plants growing in the greenhouse border. The system is connected to a water reservoir or to the mains water supply. You must monitor the rate of water delivery very carefully and adjust it according to the needs of each plant.