Proper Lawn Irrigation in Western Washington

The Pacific Northwest has a reputation for receiving more rain than other parts of the West Coast. However, about 90% of the average rainfall in the greater Seattle area comes during the fall and winter months. Between the beginning of May and the end of September, the average rainfall for this area is only 7 inches. Most turfgrass growers in Western Washington recommend giving your lawn about an inch of water per week, deducting any rainfall. Scheduling your sprinkler system to deliver this amount of water 2 to 3 times per week helps, but you may need to adjust your watering frequency or duration if the weather is too warm or for those few rainy days.

Checking the Irrigation System

Ensuring your sprinkler system is functioning properly and hitting all areas of your lawn is key to efficient irrigation. Hiring a professional to come in and inspect your system during the Spring is a great way to ensure the job is done correctly. For those DIY fans, you can check your own sprinkler system by placing empty tuna cans uniformly around your lawn. Run the sprinklers for 15 to 20 minutes and measure the water levels in each can. Make any adjustments needed to ensure each sprinkler is delivering the same amount of water at the same rate.

Sprinkler Head Volume & Calculating Watering Times

While testing how well your sprinklers are working, you can also use the water measurements to determine how much and how often to run the sprinklers. Most grasses available in the Pacific Northwest require about an inch of water per week in the summer, deducting any rainfall. Most experts also recommend watering 2 or 3 times per week as deeper watering cycles promote deeper root growth. You can check with your local government or water company to determine if there are any watering schedule restrictions in your area. Once you have measured how long it takes your sprinklers to deliver an inch of water, simply divide that watering time into 3 days per week.

When the Fall begins to bring rain, you can use weather forecasts and rainfall estimates to cut back on your supplemental irrigation.

Time of Day

Water your lawn in the morning hours during the summer. Watering in the heat of the day isn’t ideal as evaporation can prevent water from soaking into the soil. Watering at night can leave your lawn more prone to disease.

Checking Your Watering Effectiveness

Whenever your watering schedule changes, it’s best to check the lawn every week for brown spots that may signal too little or too much water. If you notice brown spots in the grass, check the moisture of the soil inside the brown spot by probing the area with a screwdriver or soil probe. Too dry means this area needs more watering. Overwatering can also produce diseases that can turn spots in the grass brown.

Moss

Moss means an area is getting too much water or too shady for healthy turfgrass growth. If you see areas of moss in your lawn, reduce shade (if possible) and aerate the soil to provide better drainage. Applying lime to raise the Ph of the soil makes a less hospitable environment for moss to grow. To eradicate areas of moss, apply Iron (Ferrous Sulfate, Iron Sulfate or Moss Out).