An adequate watering system is essential for the long-term health and vitality of your plants; this may range from a simple watering can to an automatic system such as overhead sprinklers, capillary matting, mist units, seep hoses or trickle irrigation. Automatic watering systems are useful in summer greenhouses, and are essential if you have to leave your greenhouse unattended for long periods of time during the growing season.

Watering Cans

The cheapest and most efficient way to water your greenhouse plants is by using a traditional watering can. Although more time-consuming than other systems, a watering can allows the gardener to accurately supply each individual plant with just the right amount of water.

Capillary Systems

In a capillary watering system, plants are placed onto a layer of matting which is kept moist by trailing the edge into a reservoir of water. A 2-5 cm (3/4-2 in) layer of clean sand may be used in place of the capillary matting.

In order for the system to work effectively so that it provides a continuous supply of water to the roots of the plant, there must be a good area of contact between the compost in the base of the plant pot and the source of moisture. Whilst this can be easily achieved for plants in plastic posts simply by standing the container on the moisture source, plants in clay pots may need to be provided with a wick to bridge any gaps between the compost and the mat. This may be formed by placing a small piece of capillary matting into the drainage hole of the pot so that it contacts the compost and the matting or sand.

As most plants are dormant or growing slowly during the winter, the capillary system should be removed during this time to prevent high levels of humidity damaging the plants.

Overhead Systems

Overhead sprinklers are often used in commercial greenhouses and are excellent for watering a large number of plants. However, this system can be expensive to install and is really only suitable for watering plants that are all at a similar stage of growth. Their use in winter may also create an excessively high relative humidity.

Seep Hoses

Seep hoses are plastic or rubber pipes with hundreds of minute holes along one side of their length, through which water is allowed to seep. They are used in greenhouses to water border crops or to keep capillary matting moist.

Mist Units

Mist units provide plants with a mist of water beneficial to healthy plant growth and may be used in greenhouses, conservatories or polythene tunnels. The system creates a fine, even mist of water, ideal for propagating seedlings and cuttings. The warm, damp atmosphere created by the mist prevents cuttings from wilting or scorching, allowing rapid root growth to take place.

Drip Irrigation

A drip (or trickle) irrigation system delivers water slowly and directly to plants, allowing water to be absorbed effectively by the root system. The water is slowly and consistently supplied so the roots have a chance to take up the water before it evaporates.

The system comprises of a number of thin tubes that run between pots or along beds or grow bags, with adjustable drip heads attached to the tubes wherever needed. The water is usually supplied by a reservoir: either a tank or water bag that may be refilled when necessary. This makes it an ideal automatic system for greenhouses without mains water. The rate of water delivery must be checked regularly and adjusted whenever necessary, according to the growth stage of the plants, the season and the weather.

Timers and Controllers

Water controllers and timers enable you to control greenhouse watering easily and accurately, reducing the amount of effort needed to water plants on a day-to-day basis. They are also ideal for when you are away from home.

Timers may be programmed to switch irrigation systems on and off at certain times. Some models are highly sophisticated, allowing a number of different watering periods every day with durations lasting from 1 minute to 10 hours. It may also be possible to set a different schedule for each day of the week.

Controllers are used to 'sense' the amount of soil or leaf moisture present; when the plant or compost is too dry, the sensor instructs a solenoid valve to open to allow water through the irrigation system for a pre-set amount of time.