Watering Guide

What does the math tell us?

The following section is a technical explanation and guide for watering. If you’re looking for basic watering tips and information, check out our blog post about How Much Should I Be Watering My Lawn In Utah.

In the turf care industry the number one problem plaguing us is water. So, Be sure to educate yourself on the most effective ways to water. Aside from obvious factors (misaligned heads, clogs, broken sprinkler heads, etc.) the most common watering issue you’ll face is lack of water.

Sprinkling systems are a blessing and a curse for lawn care. They provide water to lawns in areas that are prone to drought conditions and allow for cultivars to grow in areas where they shouldn’t. However, they can be wasteful and inefficient. You’ll should actively adjust yout sprinkler timer throughout the season to get the best watering results. Using the ‘set it and forget it’ method leads to two watering issues:

    • Way too much water is applied during rainy or cool seasons; Spring and Fall especially
    • Way too little water is applied during heat and drought seasons; Summer especially

So don’t just set your timer in March or April for ’20 minutes, 3 times per week’ for the whole season. Instead, make adjustments throughout the season, water less in the spring and fall and more in the summer. Dry spots in your lawn won’t usually be fixed just by watering more. Usually dry spots are related to coverage being off. Be sure to perform a cup test on your sprinkler system (watch the cup test video at the bottom of this page for more information). This knowledge is powerful because you can calculate how many inches of water each head puts out in 5 minutes. Then you can calculate how long and how often you need to water in those sections, depending on the time of year. Your goal is to provide the right amount of sprinkler water with the amount of natural rainfall received during that time of year.

Take a look at the charts below.

These are the seasonal average temperatures and rainfall for Salt Lake City Utah. This data is used to illustrate the bell curve for watering efficiency in the graph further down. We haven’t included the winter months, since they are typically too cold or have enough moisture. We have included March – November for the “Turf Growing Season”. The data includes the average daytime temperatures, average monthly precipitation, and average days of actual rainfall. The dominant grasses in Utah are Kentucky Blue (90%) and some fescues (10%). The piece missing from this chart is average daily humidity. In the summer, humidity in the high desert will average around 25. So, dry!


Jan
Feb
Mar
Apr
May
Jun
Average high in °F
38
44
53
61
71
82
Average low in °F
26
31
38
43
52
61
Av. precipitation in inch
1.46
1.5
2.2
2.32
2.09
1.14
Days with precipitation
10
9
10
9
8
5
Hours of sunshine
137
155
227
269
329
358
Average snowfall in
11
10
6
3
0
0

Jul
Aug
Sep
Oct
Nov
Dec
Average high in °F
90
89
78
65
50
40
Average low in °F
69
67
58
46
36
27
Av. precipitation in inch
0.59
0.71
1.54
1.65
1.77
1.61
Days with precipitation
4
6
5
6
7
9
Hours of sunshine
377
346
306
249
171
135
Average snowfall in
0
0
0
0
7
10

By overlaying the information above into the chart below, we can see where we need to adjust water based on what is naturally falling throughout the month. Bluegrass prefers 1.75” of water per week throughout its effective growth cycle, an average of 7” per month. That is considered healthy to maintain the Bluegrass variety. The data below shows how many inches per week of water should be applied, on average, during that month. This accounts for the average natural rainfall, average temperatures, and total rainy days during that month. Keep in mind that lower temperatures evaporate less water, which means more water remains in the soil. In the chart below, March is not listed since it is typically at 0″ of irrigation water for the month.


Irrigation
Avg. Temperature (°F)
Apr
.5
69
May
1
80
Jun
1.5
85
Jul
1.75
90
Aug
1.75
90
Sep
1.25
85
Oct
1
74
Nov
0
64

Below you will see the “bell curve” model of irrigation, which follows the growth cycle of turf. Nitrogen fertilizer feeding schedules have the exact opposite curve. For a second watering resource, check out the Utah DNR Weekly Watering Guide

Bar and line graph of precipitation and temperature over months.

So let’s run some numbers.

In April, if you apply 1/2″ of water 3 times per week that provides 6” of irrigatited water per week. For the month of Then, add that 1.5″ of sprinkler water to the average rainfall for April and you get 8.25+” of water for the month. That is a bit high and will keep roots shallow. You should run a “bell curve water program” resulting in less watering in the spring and fall, with more watering in the summer. If you follow the bell curve watering, you can save up to 25% IN OVERALL WATER. Keep in mind that season have variation. During a wet spring, you should water even less. During a dry spring, you’ll need to water a little more. The same applies for all of the other months of the year. Below is the cup test video, hope you enjoy!

Water Smart Tips - Measuring Sprinkler Output with Catch Cups