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.

Professional irrigation therefore has two principle sides. It aims to provide optimal growing conditions to the garden plants, while using as little water as possible. Does all this though have to be at the expense of the beauty of the garden? As it happens, grouping plants together that have similar water requirements also makes good design sense. In other words, plants that grow in similar habitats tend to look good together, while the opposite is also true. Here are some examples that clearly illustrate the point.

  1. Olive trees and date palms grow in radically different habitats, yet they are often planted together in Mediterranean gardens. Now ask yourself; do they go well together?
  2. I’ve seen the massively – leaved Philodendron “Beefy”, an archetypal tropical plant, planted next to the fine-leaved Pyracantha, a Mediterranean species. The look is totally incongruous. As one would expect, the tropical Philodendron requires an entirely different irrigation regime from that needed by Pyracantha.
  3. On the other hand, herbs like Rosemary and Lavender associate perfectly in visual terms with other arid and semi-arid plants like Junipers, Pistachios, Sumacs and Pomegranate. All can be grown on a similar and limited water regime, typified by deep, occasional soakings. In fact, it is not by chance that this is the case. All possess the small leaves typical of a climate where the plants reduce water loss by restricting the surface area of the organ (the leaf) through which water evaporates into the atmosphere.
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