Irrigation is the process of supplying water to land, one of the oldest and most important agricultural techniques in the world. Irrigation has allowed farmers to grow crops on land that would normally be unproductive due to lack of moisture in the soil for thousands of years. In the UK residential gardens can often do without irrigation for most of the year, but obviously those looking to grow their own vegetables would struggle if the soil was too dry. So some sort of irrigation system may be required for an attractive and manageable garden all year round.
Large scale irrigation can involve deliberate flooding, canals, and even computer controlled machinery, but these methods are confined to large agricultural developments, though horticulturists can use the same techniques in scaled down versions. Installation of even small scale irrigation systems is often a professional task, but some types of irrigation systems can be employed for the home garden. The rate at which water passes through the ground (infiltration rate) is mainly dictated by the type of soil, but plant cover plays a small part too. The main categories of soil are gravel, sand/silt and clay.
Gravel type soil holds very little water owing to the large gaps and water passes through quickly. Sand/Silt soils have a medium to high infiltration rate, whereas clay type soil is the most compact soil type in the UK with a very low infiltration rate. In general, small amounts of water need be regularly applied to most types of soil in the UK. The installation of an irrigation system can involve a lot of work, so is best considered when planning a landscaping a garden. If the garden is to be built on bare ground, the area to be irrigated can be deliberately landscaped into the overall design. Before any irrigation system is installed, the garden needs to be split into irrigation zones which have different requirements depending on drainage, soil type, aspect and plant type.
Good drainage is crucial in gardens for many plant types. Installing drainage on wet soils is one of the most effective things a gardener can do to improve growing conditions. Drainage although important, does not mean that every garden needs installed drainage. Many gardens will have sufficient drainage thanks to nearby ditches, streams or soakaways. Drainage problems occur when there is nowhere for excess water to go, turning gardens into bogs.
The first thing to do is to identify poor drainage areas, look for surface puddling after rainfall which normally indicates the soil may benefit from installing drainage. But before installing a drainage system consider simply digging the beds and adding organic matter. If that fails then digging simple ditches can often be enough to take excess surface water. Where open ditches are unsuitable you can construct French ditches by filling the ditch with coarse gravel topped with permeable membranes or upturned turf.