Well..when it is dry, watering your lawn is the obvious thing to do. However, the correct time to water your lawn is at a time when it is least wasteful, least able to cause damage, and in turn is most useful and beneficial to the lawn. Therefore, watering your lawn in the morning is the best time.
Lawns, and all other plants have the same sleeping patterns as we do. They spend some of their time awake and other times asleep, and like most of us, lawns will be awake during the day, and asleep at night. During its awake time, the lawn is actively absorbing water from the ground, conducting photosynthesis, creating it's food, and growing. While asleep, the lawn becomes dormant, and these growth and life habits considerably slow down to an almost complete halt. The lawn will no longer absorb water, produce food, or grow in any but an absolute minimalist manner. You see, the vascular system of lawns works a bit like our blood stream. Pumping nutrients and water from the ground, and distributing them around the plant. This vascular system is powered by the sun, and as such is active during the day and shuts down at night.
Wasting Water At Night
With the extreme hot summer temperatures Australia is presently having, every home-owner or renter is understandably tempted to migrate outside late at night. And, in turn, we naturally look at the lawn and reach for the hose to water and cool things down. Unfortunately, this is the wrong thing to do.
When lawn watering at night, the lawn can make no immediate use of the water it is receiving, so the lawn does not absorb it, and it stays in the ground being pulled down towards the water table and away from the root zone of the lawn. By morning when the lawn wakes and requires water, much of it has already disappeared, and cannot be used by the lawn at all. This results in an unnecessary waste of water that was never used, unhealthy lawns lacking adequate water, or too much water having to be applied in order that enough is left over in the morning for the lawn to use, and to show adequate health and growth.
Outside of excess water wastage, watering at night creates a lingering moist environment which can promote lawn disease such as Spring Dead Spot, as well as other fungal infestations which can damage lawns and hinder their appearance.