Thinning lawn - Ask Extension
Please see the attached photo. The turf gets water 4x per week in the heat of summer and is thinning. Please let me know what you need for further d...
Knowledgebase
Thinning lawn #913971
Asked August 14, 2025, 8:40 AM EDT
Please see the attached photo. The turf gets water 4x per week in the heat of summer and is thinning. Please let me know what you need for further diagnosis. The healthy and unhealthy grasses are both firm when I try to pull them up, so I do not think it is grubs. The mowing company said it was rabbits, but there are not rabbit pellets in any of the areas and the lawn next to the home looks fine. What other possible causes are there? Thank you in advance for your help!
Larimer County Colorado
Expert Response
Hi Susan,
Believe it or not, I think some of this is drought stress. It's just so hot and dry. Though you're watering four times per week, do you know how much water you're applying to the lawn each time you water? I would suggest that you do an irrigation audit to collect the water, look carefully at the heads, and then make adjustments. The steps are below:
For the irrigation audit, follow these steps:
At the very least, the audit will rule out irrigation as a potential cause of the turf stress. But I do believe the issues are linked to irrigation.
Believe it or not, I think some of this is drought stress. It's just so hot and dry. Though you're watering four times per week, do you know how much water you're applying to the lawn each time you water? I would suggest that you do an irrigation audit to collect the water, look carefully at the heads, and then make adjustments. The steps are below:
For the irrigation audit, follow these steps:
- Put out several (10-12) cups of uniform shape and size in an irrigation zone. You can use tuna cans, yogurt cups, etc. Be sure to place some in the green spots and some in the brown spots.
- Run the system for 15-20 minutes.
- While the system is running, look carefully at the heads. If there are heads that are crooked (even slightly), not popping up fully, or at an angle, flag those heads to adjust later.
- After the system runs, measure the water in the cups and compare the output. Are the thin spots/brown spots getting less water? Even a slight difference of 0.10" can lead to INCHES over a growing season. Do the thin/bare areas correspond to any heads that are crooked or not popping up fully?
- Adjust your heads. Make sure they are rising above the turf surface, have a good angle, the pattern applies water evenly, and they are nice and straight.
- Set out the cups again after your adjustments and run the system again. See if you have improved outputs that are more even.
- Measuring your output will help determine how long you need to water each week in minutes. If you get 1/4" of irrigation in 20 minutes, then you'll get 3/4" in 60 minutes. So to apply 1.0" of water, you'll need to water a total of 80 minutes during the week. This might mean two, 40-minute cycles or 3, 26-minute cycles. The seasonal needs of typical bluegrass are:
- April: 0.5"/week (this includes precipitation too!)
- May: 0.5-1.0"/week
- June: 1.0"/week
- July: 1.0-1.5"/week
- August: 1.5"/week (right now, with the heat, it's not unreasonable to apply closer to 2"/week)
- September: 1.0" week
At the very least, the audit will rule out irrigation as a potential cause of the turf stress. But I do believe the issues are linked to irrigation.
