Watering Lawn

Just about everywhere I look, it says you shouldn’t water your lawn during the middle of a hot sunny day. While this makes sense from an evaporation standpoint, the reason usually given is that the water droplets will focus the sun’s rays and burn the grass.

From my understanding of optics and heat transfer, this sounds like a load of bull. The focal point would be well below the surface of the grass, and the water itself would prevent the surface of the leaf from becoming too hot (evaporation would cool the leaf).

Any comments?

I don’t water my lawn period. Of course, it rains a lot here. I remember when I first moved in and my lawn was nothing but dirt, I watered twice a day, once in the morning and once in the evening when I got home. I have really nice grass now(except for my back yard for some reason).

When plants are irrigated, they aquire a thin film of water over the leaf surface which is a solution of salts and minerals. A change of concentration occurrs when this water evaporates rapidly in the sun. This has an osmotic effect on the leaf which draws water from the leaf to the high salt concentration on the surface. This has the effect of dessicating the leaf and leaving a salty crust behind.

More of a chemical burn than sun burn.

Healthy lawn tips , including some watering info.

If your city water is expensive, it is a waste to water in the heat of the day due to evaporation. Never water late in the afternoon or at night due to getting a grass fungus. I have my sprinkler system set to water at 6 AM. This will allow the lawn to completely dry before night. I live on a lake so I have plenty free water… just a little electricity to run the pump.

But… I previously lived in a desert, irrigated farming was big business… during the growing season, they watered around the clock. Watering in the hot sun sure didn’t hurt the cotton and other crops.

This is because they watered, and to quote you,’…around the clock. Therefore the process which I described above cannot occur

This is because they watered, and to quote you,’…around the clock.’ Therefore the process which I described above cannot occur

Yes, they water around the clock, they use a moving sprinkler system. But the plants only receive water for a given time, all plants are not watered 24 hrs a day. Therefore some of the plants are watered in the hot sun and my be left with water on the leaves in the hot sun.

Aside from the “burnt grass”*another reason for not watering during the heat of the day is the plants will not transpire when it it hot. They sort of seal themselves up so to speak to conserve moisture. The best time to water grass or another plants is in the early morning, as this is the time of the day the plants “drink”.

*Here in Vegas your lawn will scortch in the sun if watered during the day. Plus here it is now prohibited to water from 11 am- 7pm but that is for water conservation/evaporation reasons.

If you live in a transition zone, where it’s too damn hot in summer for northern grasses like blue, rye and fescue (but you are too north to grow southern grasses) , there could be a benefit to watering during a very hot day: to cool the grass and soil.

If you are growing bluegrass, and you stick to the traditional 2-3 watering schedule, you could see your grass struggle terribly when a heat wave hits and the grass is baking in 90-99 degree weather for a week or more.

You could find great success in staving off weak grass by throwing in a couple of light waterings during the mid-day. The evaporation will act to cool the grass/soil.

In areas where there exists a battle to grow northern grasses in very hot summmer months, and where the soil is less than perfect, bluegrass/rye/fescue can dry out in one day. This would make it very prone to insect damage and fungus.

A couple of heavy weekly waterings where the soil drains very well might not suffice. A god trick would be to pepper in some light watering during the mid-day heat.

There are individuals challenges depending on where you live that don’t always fall under the umbrella of the generic lawn care advice sites.