Landscaper Pro Advice: Moisture Management and Irrigation

If a lawn is to sustain healthy growth and density as well as displaying an attractive colour the constant availability of water to the plant roots is essential.

A soil is considered to be deficient of water where transpiration from plant leaves is greater than the amount of water that can be taken up by the roots.  This results in stress, which if allowed to persist, will cause wilting and the turf will develop a brown appearance.  As a consequence the grass plants are weakened and become more vulnerable to diseases such as anthracnose and conditions such as dry patch.

The ultimate long-term consequence of water deficiency is grass death.  The speed at which this occurs is dependant on a number of factors including sward species composition and height of cut.  Closely mown turf tends to have a shallower root system and therefore will tend to die first, as will annual meadow grass which is naturally shallow rooted compared with bent and fescue species of grass.

How do I know if I need to apply water?

Regular checks of the soil profile should be made during periods of dry weather to determine the need to apply water.  This can be done physically using a soil augur to remove cores and check the current moisture held within the soil or by using a good quality moisture meter.  In either case cores/readings should be taken across the entire site to give a representative sample of results rather than from a single location.

Lawns with a high level of organic matter at the surface, compacted soil and turf which is over fertilised and over-watered will all have poor root systems and as such will be more vulnerable to drought stress.  As such, symptoms may be displayed despite moisture being present in the soil.  In such instances applying water is simply providing a short-term measure of improvement rather than a long-term solution to deeper underlying issues.

Top tips for good moisture management

The best approach for managing moisture levels will vary from site to site and according to the equipment available. The following tips include basic maintenance strategies that should be considered and adopted where feasible:

• Always raise the height of cut to allow the grass plants to better cope with stress through a dry period.
• Keep the soil profile moist (not wet) during hot and dry weather to ensure a constant supply of water is available and to minimise stress.
• For more routine weather conditions allow for wetting and drying cycles, watering deeply only when required.
• Do not apply water too heavily. Instead choose light applications applied over a longer period to allow the applied water to be absorbed.  This will minimise the amount of run-off and result in a more uniform re-wetting of the soil.  Where heavy applications are made in a rush, low sections of ground are prone to over-watering whilst high spots remain dry resulting in uneven growth.
• Aerate the surface prior to watering to improve the infiltration capacity of the soil, especially if it has been allowed to dry out.
• If practical, apply water in the evening or overnight when losses to transpiration will be minimised. This is easier where an automatic irrigation system is available.
• Consider using a wetting agent to assist the penetration of water into the soil, especially if it has been allowed to dry out and/or has developed hydrophobic characteristics (water repellency).
• Use a moisture meter to check moisture levels with the aim of maintaining a consistent level of moisture of between 25-35 %.

Can I apply to much water?

Over-watering wastes water.  Over watering will encourage the weed grass annual meadow grass at the expense of the more desirable grass species (bent, fescue, ryegrass etc.). Over-watered turf will also develop a shallow root system and high levels of organic matter and as a consequence the area will decline in quality and become more vulnerable to drought and disease infections as well as deteriorating in its response to fertiliser inputs.