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Lawn Care Blog

3 Steps to Calculate How Much Water Your Lawn Needs

Watering your lawn should seem like a pretty easy concept. However, do you really know how long you should be watering? Chances are that when lawn care companies tell you to provide your lawn with one (1) inch of water a week, your mind goes a bit fuzzy. Like when we're lost, most of us won't admit that we may need a bit of help to figure out how long we should run our sprinkling system for to give our lawn that 1-2 inches per week that it needs. Well Magellan, your in luck! We'll calculate how long you should be watering your lawn in 3 easy steps.

irrigation diagram1. Proper Sprinkler System Spacing & Gallons Per Minute - When the landscaping company installed your irrigation system, they use a technique called "head-to-head" spacing. This is where the sprinkler heads are placed in a grid, with each heads spray pattern reaching the heads next to it.

The diagram to the right shows four (4) sprinkler heads spaced "head-to-head." Spacing depends on the amount of water that each sprinkler head puts out. In this example, each sprinkler head emits two (2) gallons per minute. (In fact, most manufactures write on the sprinkler head how many gallons it emits.) At this rate, the sprinkler throws it's water approximately thirty (30) feet away. Placing sprinklers in a "head-to-head" grid like this, ensures equal amounts of water over your lawn.

2. The precipitation Rate Equation - To provide the adequate amount of water for your lawn care fertilizer program to be effective, a certain amount of water is needed. During the typical lawn care season, your lawn requires an inch (1) of water every week to keep it properly hydrated and growing strong. During times of extreme heat and stress, due to the lack of natural moisture, your lawn could need three to four (3-4) inches of water a week.

PR equationThe precipitation Rate Equation is used to calculate how much water your sprinkling system provides your lawn. The calculation, shown on the right, is 96.3 (a constant of inches per square foot per hour) multiplied by the Gallons Per Minute applied to the area, divided by the spacing between the sprinklers, multiplied by the spacing between the rows of sprinklers. 

PR finished equationFor the example area diagrammed above, the four (4) sprinklers put out two (2) gallons per minute of water, equaling eight (8) gallons per minute to the area. Next, the spacing between each sprinkler head is an even thirty (30) feet. Additionally, thirty (30) feet separates the two rows of sprinkler heads. So when we calculate the formula, the area being watered receives almost one inch (.856) of water an hour.

3. Programing your Sprinkling System - After calculating how much water your lawn is receiving from your sprinkler system, adjusting your sprinkler run times is the next step. Remember that during normal spring like conditions, your lawn should receive one (1) inch of water a week. With this being said, and using the above example, you should water that area of your lawn for twenty (20) minutes, three (3) times a week.

However, if we are experiencing a drought and your lawn care company asks you to apply three (3) inches of water a week to that area, you'll need to water for approximately three (3) hours a week. In this case, you would increase the sprinkler system run time for that area to perhaps forty-five (45) minutes, four (4) times a week.

Programming Your Sprinkler System Controller - Of course now that you know how much water you should be applying to your lawn, the next challenge is actually changing the settings in your sprinkler system controller. Check out our YouTube video featuring two of the most common manufacturers:

More Information On Watering During Drought Conditions

Now that you're armed with the proper amount of water needed, and how to adjust your sprinkler systems accordingly, how about learning some ways to cut down on the costs of your watering? Check out Weed Pro's Summer Watering Guide for tips and tricks on how you can water your lawn properly, and save money by doing it.

Free Lawn Care Watering Guide!


Shaun Kanary 
has been a part of the Green Industry for the past 15 years. As the Director of Marketing for Weed Pro Lawn Care, a Cleveland and Columbus Lawn Care Service Provider, Shaun is a regular contributor to the Weed Pro Blog, and other industry magazine and blogs. 

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