Lawn Watering: How Often? How Much?

Summary: Lawn Watering – “When to water a lawn”, “How long to water the lawn” and “How often should I water my lawn” are questions most lawn owners want the answers to. In this article we will provide some tips and guidelines on lawn watering to help homeowners produce strong, healthy grass.

Question: When, how long and how often should I water my lawn? It seems to be a very simple question, most of my buddies at the office just say they set their irrigation timers and let them go. But, I’ve seen some of their lawns and don’t think they have a clue. Can you give a simple answer on water the lawn? Alex, Fayetteville, NC

Answer: Alex, the topic of watering lawns probably generates more questions than any other area of lawn care – even more than lawn fertilizing.

The task of watering the lawn is certainly one many homeowners do not understand. They assume a little bit is good and a little more (water) is better, but when it comes to putting water on the lawn – more is not always the best policy.

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Many elements and conditions play a part in an efficient lawn irrigation system and all contribute to the development of a good watering schedule. How much and how often to water would be simple if there were not so many factors and variables that come into play. Here are a few of the factors to consider:

  • Rate or Speed Of Water Penetration
  • Soil Water Holding Capacity
  • Depth Of Grass Root System
  • Rate and Speed Of Water Loss
  • “Guidelines” of the Water Management District and water conservation
  • Grass type: warm-season grass or cool season grass and if the grass is a drought tolerant variety

Rate or Speed Of Water Penetration

The type of soil in your yard will influence how fast the water will penetrate and percolate into and through the soil.

In a clay type soil (soil which is very tight leaving little room for air) the water slowly penetrates and seeps through the tight soil. The average sprinkler head can deliver water faster than the soil can absorb it. This creates runoff and puddling in low spots.

On the flip side, when water is put on sandy soils (soils which are open with lots of drainage), the water will quickly drain right through the soil.

To find out what kind of soil you have – start with a soil test. This will help in determining water schedule, times and duration as you do not want to waste water by running the sprinklers too long.

But, also not running the irrigation system long enough (water pressure can also play a role) to allow proper water penetration into soil of the lawn.

Soil Water Holding Capacity

Every soil type, from sandy soil to clay soils each have their own capacity to hold water. Sandy soils are made of larger soil particles than clay soils holding less water.

For example: If you were to take 100 square feet (10 x 10 feet) of sandy soil measured 1 foot deep you would find approximately 60 gallons of water in the soil.

Whereas, if the same 100 square feet of clay soil 1 foot deep was measured, the clay soil would hold approximately 160 gallons of water, over 2 1/2 times as much.

From this example you can see that sandy or “lighter” soil will need to have a more frequent lawn watering schedule than the clay soil.

Depth Of Grass Root System

When you pull up a handful of grass from your lawn you find roots 3 to 6 inches long.

Often that is how long many people assume – how deep the roots in the turf travel. These are only “surface roots”, in reality grass roots can (depending on the grass and soil type) reach down 24 – 30 inches.

If you could take a cross section and look at the above 100 square foot example and realize that the roots of your lawn can reach down to cover a soil block of 200 – 300 cubic feet, it is possible the soil where the root system lives is in fact holding 120 to over 300 gallons or more of water.

Rate and Speed Of Water Loss

The water held in the soil over time either evaporates or is lost through transpiration (water loss through leaf surfaces).

As temperatures rise, sun is more intense and/or winds increase, plants – grass included – must work harder to stay hydrated (just as people do), this increases the rate of transpiration.

Other plants and trees in the landscape also compete for moisture in the soil. Grass can function as a moisture insulator for the landscape.

On average, soil will lose 1 – 2 inches of water per week and through nature or irrigation the water must be replaced. As weather changes, water may need to be increased or decreased.

Now that you have some “soil science” background

When, How Often and How Long To Water A Lawn

The simple answer to “How often should you water your lawn?” – not to be a wise guy but the real answer is – When your lawn needs it! However, your water management district may have some control of the WHEN.

When the soil drys out, the grass will slowly begin to wilt, change color and the grass when walked on, does not spring back.

As we have learned the root zone of grass is much deeper than 3 – 6 inches, so deep watering once every week will help get the moisture and water deep down into the soil.

Deep watering once per week will probably take 2 – 3 hours allowing the water to slowly soak down deep into the soil. Watering on a daily or every other day has its downsides (disadvantages of watering lightly below)

Putting down one inch of water on the surface of 100 square feet of lawn will equal about 60 gallons. On average a sprinkler under “normal water pressure” will need to run about 2 hours to put down 1″ inch of water on a lawn.

To see how much water your sprinkler system puts out, place coffee cans, a rain guage or something similar to record how much water is put down during an hour.

The disadvantages of watering lightly every day.

  • More overall water use
  • Lawn develops shallow root system
  • Lawn drys out quickly
  • Soil compaction
  • Salt build up from lack of water not leaching and moving through soil

Know Your Lawn For a Healthy Lawn

Paying attention to how your lawn reacts to your lawn watering schedule and grass fertilizer schedule will help you discover “signals and signs” to make adjustments to seasons and weather conditions.

Find out what kind of soil makes up your lawn. Check how much water and how long it takes to apply 1″ of water and make adjustments to apply enough water for your lawn for your climate and grass type. And finally, water deeply and thoroughly.

Image: MelvinSchlubman

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