Watering plants in feature beds

Watering large feature beds successfully relies on keeping the soil evenly moist. This means that deep-rooted trees and shallow-rooted underplants will all get the water they need.

Different ways of watering feature beds

There are two main ways of watering feature beds, depending on how the bed was designed.

Subterranean irrigation
Many large feature beds are fitted with a subterranean irrigation system.  This may be in the form of a self-contained system such as the Mona Link System, or a system that is directly connected to the building's water supply. If you have a bed fitted with such a system you should consider the following.

• The capacity of the system. Can it deliver enough water to the plants to keep them healthy between programmed irrigations? In a well-lit atrium during the spring and summer, you may need to give 10 - 20 litres of water for every square metre of soil surface.

• If your feature bed has a mixture of trees and underplants, watering by subterranean irrigation alone may not be sufficient. Water from the irrigation system will reach the tree's roots, but may not rise far enough to reach the roots of the small plants near by. If this is the case, top watering will also be required.  However, if you only have large trees, such as in tree pits or purpose-built tree containers, then you may find that subterranean irrigation is the ideal solution.
  

Top watering with a hose-pipe
When watering a feature bed, you should remember that you are watering the soil, not individual plants.

Spot watering individual plants is bad practice as it is time consuming and actually results in under watering over time. The reason for that is because if you only water around the plants, the rest of the soil gets very dry. When that happens, the water you add will be drawn away from the wet area into the dry soil quicker than the plant can get at it. This may result in having to make more plant replacements.

	This picture shows what happens when you spot water around a large tree. The water will pass straight through the soil, beyond the roots and into empty soil. The small plants will be in very dry soil and the tree will not be able to make use of most of the water that it has been given.
	This picture shows the ideal way to top water a feature bed. The water is added uniformly ensuring that soil is evenly moist to a depth of approximately 50 cm. This means that small plants and the large tree all get the water they need.

Adding the right amount of water
You might be surprised at how long it takes to deliver enough water to a feature bed to get it to the correct moisture level. However, once it is at the right level, you will need to water much less often.

With a typical dry soil, you will need to add 10 - 20 litres of water for every square metre of soil surface. That means a bed that is 4 m X 3 m (i.e. 12 square metres) will need between 120 and 240 litres of water. The amount of water needed will depend on factors such as soil type, density and air-filled porosity.