Most home gardeners are probably aware of the detrimental effects of over-watering. Quite apart from the desire to save water, there is a vague recognition that excessive watering is bad for the plants. It is common to find in garden literature for example, references to this or that plant that is “sensitive to over-watering”. By understanding this term more precisely however, you can irrigate more effectively, and manage the water at your disposal more efficiently.
Effective irrigation and efficient water management are about supplying suitable quantities of water to the garden plants, at the right intervals. Both these parameters differ in accordance with various groups of plants. Trees and shrubs of tropical origin may thrive on soil conditions that are almost permanently moist, while species from dry climates invariably prefer the soil to dry out somewhat between the waterings. Herbaceous flowering plants need to be watered frequently, while under such a regime, herbs are liable to suffer from a lack of air in the root zone.
The cardinal rule of garden irrigation is therefore to install separate lines for the different groups of plants that make up the garden. While sprinklers are used for lawn irrigation, drip irrigation is more suitable for the rest of the garden plants. Needless to say, both have to be separated from each other, to avoid them being operated together.
In addition, separate taps for drip irrigation should be installed for those groups of plants that have different watering requirements. The greater the separation, the more accurately one can calculate the quantities needed and fix the intervals between each watering. For example, in a hypothetical garden in Southern California, entirely independent lines would be installed for the shaded beds containing ferns and tropical fruit trees, the mass of water–conserving shrubs and landscaping trees, the herb garden planted in a bed of pebbles, and the annual flowers growing in pots.