18 March 2007

Lawn Watering Comments

Today it is raining in the Atlanta area, which brings to mind a few things to remember about watering your lawn (hose-end sprinklers and in-ground irrigation systems). There are three or four general rules of thumb, which will address 85% of lawn and turf watering issues and mistakes. I've addressed Atlanta area irrigation settings in the past.

  1. First, lawns need about an inch of water per week.
  2. This inch should be delivered in as few waterings as possible.
  3. You need to actually measure how long it takes to deliver the inch
  4. The water needs to actually be absorbed by the soil, so runoff needs to be minimized.

These rules of thumb result in a number of specific things that you should do:

1. An inch of water. The inch of water needs to be actually measured, especially if you are using hoses and hose end sprinklers. With an in-ground irrigation system, the best way is to measure the amount of water. But it is also possible to calculate the water delivery based on system design, head placement, head properties, water pressure, and water volume. These calculations would be done for each lawn irrigation zone.

Measuring an inch of water is very simple. Place a number of straight sided containers around the lawn (e.g., empty tuna fish cans). With a marker measure and mark an inch on the inside of each can. Start a timer (e.g., note the time on your watch). Run the system until the water level reaches the marks. Stop your timer. That is how long it takes to deliver an inch of water to your lawn.

It is important to place a number of cans around, and take the average between them, because the actual distribution of water will vary, regardless of whether your using a hose end lawn sprinkler, or an inground irrigation system. Even the best designed systems will have variances.

Note: Rain rarely yields an inch a week. If it rains, it does not mean your watering for the week is done. Rain is very deceptive. It may rain all night, but only yield a quarter inch. The only way to actually account for rain, is to use a rain gauge. Barring that, it may replace a single watering session.

2. No run-off. The next thing is to minimize run-off. Putting down an inch means nothing, if three quarters of it runs into the gutter. This is very simple. Start your timer again. Run the system. Observe until you see water running of the lawn and onto driveways, walkways, gutters, etc. Stop your timer. Note the time. This is the length of time you should run the system per session.

Various factors will affect run-off:
The slope of your lawn. Here, in the Atlanta area, many yards have steep slopes. Most yards will have at least one section (backyard, front lawn, side yard) which has a slope.
Soil types will also have an affect. Again, in Metro Atlanta, we have clay soils, which absorb water more slowly.
Soil compaction. Aeration will help to relieve soil compaction, among other things, helping to increase absorbtion rates.
3. Watering frequency. The final thing to do is to take the time to run-off, divide that into the amount of time it takes to deliver an inch, and that gives you the number of watering you need per week for each area of your lawn. For example, if it takes 45 minutes to put down an inch of water, and it takes 15 minutes before water begins to run off, then I need 3 watering sessions per week to give me an inch.

Space the sessions out over the week, and time them for early in the morning (best), or if necessary late at night (OK). Do not water early in the evening. This can lead to fungal problems. Avoid watering during the day--evaporation will waste water and mess up our calculations.

If your area has watering restrictions, as we do in many area of Georgia, and especially in Metro Atlanta, then this adds another layer. I've discussed Atlanta area watering restrictions in a past, and will address them again soon.

There are many other related issues, which I will address over time. Rain barrels, grey water, ponds, lakes and pumps, well water, bedding plant needs.

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