The right way to water a lawn during mid-summer temperatures
Green lawns needs water
Watering is one of the most important practices for maintaining a lawn, especially when natural rainfall is insufficient. Depending on sunlight, temperature, wind, etc., a lawn requires about 20 to 25 litres of water per square metre per week.
A common mistake is watering a lawn too frequently and too little each time. During the dry summer season, lawns are often lightly watered almost every evening. This leads to water only wetting the existing thatch and, at best, the top few millimetres of soil. The lawn responds to this, imperceptibly for the layman, by the roots becoming concentrated very near the surface of the soil. The incidence of undesirable types of grass, such as Poa annua (annual meadow grass) or Agrostis (bentgrasses), also increases. While the latter are very important for golf greens, which are watered daily and cut to a few millimetres, they create excessive matting and less resilient turf in private gardens. Thatch cultivated in this way absorbs the sparse water like a sponge and the water then evaporates from the thatch without being used. This means that the ground underneath it no longer becomes sufficiently moist and thus the effect is intensified: you could say that the lawn becomes "addicted" to water. If watering doesn't happen for a few days, the lawn quickly becomes yellow and its susceptibility to fungal diseases rapidly increases.
How can you avoid this? Water only once a week but be sure to use about 20 litres of water per square metre. If the soil is loamy and can't absorb this amount of water in one go, water twice in quick succession (or for example again the next day) and then don't water again for a week!
To check whether you have used the "right" amount of water, use a water meter or place many cylindrical glasses (e.g. even jam jars) on the lawn – after watering there should be approx. 2 cm of water in each of the glasses! Once you have done this a few times, you will know how long you need to water for. You will be amazed at the amount of watering required to reach the specified amount. Stick a sturdy blade approx. 10 cm into the ground and try to extract a soil sample each time – the samples should be moist (not wet) at the bottom, the upper 1 to 2 cm can and should feel dry! It should never be the reverse (moist at the top, dry at the bottom).
Too much water is also harmful for a lawn, although this is a rare occurrence in private gardens. Excess water displaces the air from soil pores, resulting in root rot. Always smell a soil sample: if it "stinks" or displays grey-blue discolouration, there is a lack of air and water blockage.
A "correctly" watered lawn is much more resilient, less prone to disease and exhibits a deep root system. If you have watered "incorrectly" for a long time and therefore have a "spoilt" lawn, don't radically change your watering habits. Instead, adjust them slowly and gradually (over about two months).
VIKING garden expert
Prof. Karl E. Schönthaler