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Rhode Island receives 40 to 50 inches of rain a year. However, during the growing season, there can be periods of little to no rain, causing plants to suffer from drought stress and many of us to reach for the sprinkler. How do we know we are applying enough water while not overwatering?

A rain gauge is one of the most important tools in your home landscape. With it you can properly manage lawn and garden watering. Summer showers are often spotty and unpredictable. The only way to know how much rain we’re getting is to measure it using a rain gauge. While drought stress can impact plants, over-watering creates many concerns such as:

· Increases risk of pollution from yard and garden care chemicals
· Wastes valuable water and impacts water supplies
· Encourages shallow root zones and increases plant’s susceptibility to disease
· Wastes time and money – it costs money to irrigate

Using the rain gauge, you measure rainfall and other precipitation events, such as heavy dew and mist. Most lawns and gardens need about one inch of water each week. By measuring and recording rainfall, you will have an accurate account of what nature has already supplied. You should water only to make up the difference. As a result, you should not set your watering on an automatic schedule.

Where to place your rain gauge:
Rain gauges should be placed in an open area away from trees, buildings, and other structures, as they may cause the rain gauge to get a false reading. Ideal areas to place rain gauges are in open areas attached to posts or stuck in the ground. A good general guideline to follow is placing the rain gauge twice as far away from the height of an object such as a tree.

The rain gauge you may have just received contains a 5” rain gauge and 1” watering gauge to measure irrigation sprinkler output. To use the rain gauge
on the ground, place the 1” watering gauge in the ground (part with the plastic spike), then place the 5” rain gauge inside. If mounting on a post, the rain gauge can be screwed on separately from the 1” watering gauge.

If you obtain your own rain gauge, depending on the type, it may be made for mounting on a post with a screw, stuck into the ground with a plastic or metal spike, or stand on the ground with a special holder. Some holders are specially designed to add decoration to the garden. Check with your local garden supply or hardware store.

Using your rain gauge:
After you install your rain gauge you will need to check it at about the same time once each day and record the amount of precipitation collected. If you do not check your rain gauge each day evaporation could distort your reading. Make sure to take the reading at eye level to avoid error. Be sure to empty the rain gauge each day after your check it. Add your daily rain measurements at the end of each week to obtain your weekly precipitation amount. If the total weekly rainfall is less then one inch, the difference can be supplied with irrigation. Before irrigating check the weather forecast and for signs of drought stress in your lawn or garden. For more information on proper watering and identifying drought stress, refer to the Water Wisely factsheet.

Measuring Sprinkler Output:
The 1” watering gauge can be used to collect water from your sprinklers so you know how much water is being applied. You can also use a bake pan or shallow can such as a tuna can if you do not have an extra rain gauge or special watering gauge. Place your watering gauge or can within the wetted path or radius of the sprinkler just prior to watering. Avoid placing at the extreme outer edge of your sprinkler’s wetted path.

When watering is complete, read and record your watering gauge. If using a pan or shallow can, take it to a flat surface and measure the depth of water with a measuring stick.

Here is an easy way to calculate sprinkler output:
· Run the sprinkler system for 30 minutes.
· Measure the amount of water collected in your watering gauge, pan or shallow can.
· Multiply that depth by 2 to get the amount of water that your sprinkler applies over a one hour period.

Adjust the flow rate and running time of the sprinkler to apply the amount of water intended without causing runoff.

For example, your sprinklers ran for 30 minutes and you collected ¾” of water. Multiplying ¾” by 2 equals 1.5 inches over a one hour period. You thought you were applying ½” over 30 minutes, or 1” over a one-hour period.

Next time you irrigate, you can reduce the flow rate (gallons per minute) as needed to result in ½” over 30 minutes or 1” over a one-hour period. You can figure this out through trial and error. If the flow rate is set and not contributing to runoff problems then simply reduce the running time. For example, you could reduce the watering time to 20 minutes and then measure again to see if you are now at ½”.

For more information:
See our Water Wisely fact sheet