Root depth - how do I train plants?


I have Marathon tall fescue in the front, St. Augustine in the back, ferns and hibiscus in planters, and trees and some shrubs in another area. I’ve measured my water flow via 8 catch cups and averaged it. Each zone is 750 sq ft or less (planters are less than 200 sq ft). I used that to set my in/hr via custom nozzles.

While my Iro seems to be doing its job quite well, everything seems a little starved for water. For example, my fescue is looking a little blue/grey and the leaves are curving up today, but it’s set to water tomorrow.

My prior irrigation system was watering about every 2-3 days. My theory is that my root depths aren’t what the Iro set for the pre-programming. I think I may have caused my plants to have a shallower root depth by in appropriately watering more often than necessary?

I was hoping someone could comment on whether or not my theory is likely correct, and if so, how do I fix it (in southern California, in case that’s relevant).


  • Garrett


@grit I’ve forwarded this along to our support team. We have a few experts that hopefully can weigh in on this :wink:

In the meantime, here is some more information on flex dials and levers.

Also, if you just want to increase watering frequency you can modify the managed allowed depletion (MAD) on advanced zone settings.

Maybe try lowering it by 10%-15% and see how the predicted flex calendar looks. By lowering MAD your watering frequency will increase, but your run times will slightly decrease.

Hope this helps.



Great question! I am also interested in hearing expert opinions on that. I would think the best approach for your situation would be to do nothing because the grass is only “a little starved for water”. Creating a little stress before watering is perfect training for deeper roots. If the stress shows up more than one day in advance of a watering event, then I would temporarily decrease MAD, to say 40%. Then periodically raise it until you get back up to the default 50%. Decreasing MAD will increase frequency of watering closer to what you were at before. At the same time, it will decrease the amount of water applied so that you are not wasting water. It would be helpful for folks to know what frequency your current flex schedule is running at. You stated prior settings (old controller) watered every 2-3 days. Is it now about 5-7 days? Does anybody know how fast roots grow, and how quickly the MAD should be increased back to 50%?

Also, check out this site for encouraging root growth. Improving Grass Root Growth. The basic principles listed are

  1. Mow height should be 3-4 inches
  2. Don’t water until blades start to show signs of drought stress
  3. Use a slow release fertilizer that is formulated to stimulate root growth


Sorry, I should have specified I’m using Flex scheduling, though I suppose that’s apparent now. I’m using a weather station at a nearby small airport in San Diego county (CA), about 3 miles away. While my micro-climate is consistently 3 or so degrees warmer, the weather should be pretty accurate.

The fescue typically waters every 4-6 days, the St Augustine every 6-8 days. The planters run about every 5-8 days.

I may have understated the apparent water loss/stress. I’ve been overriding the system to give more water by forcibly depleting the soil moisture level to zero when the grass/plants/etc look stressed. The fescue (for example) is starting to look stressed again. It watered this morning but the grass doesn’t look any better, so I assume it’s still stressed?

I read the provided links. They describe what I’m seeing better than I did: “… the blades will fold, which shows the lighter blueish green underside.” I mow down to at about 2"-2.5", but that’s per Marathon: “Height: Summer, 2-1/2” mowing height recommended. Winter, 2" mowing height recommended." Is that wrong?

Two days ago, I changed the root depth for the fescue zone from it’s default 6" to 5", which seems to have moved the watering schedule up to every 2-3 days now. I hadn’t thought of changing the MAD, but I’ll do that instead, since it’s more accurate to leave the root depth as it should be.

For lawn care, I use Marathon fertilizer about every 6-8 weeks. I use a 25-5-5 (as directed), except around late October and again in mid to late march, when I use their 15-15-15. In San Diego, it doesn’t “cool off” until Halloween (that’s roughly the last day you can wear shorts at night). And by mid march, the cool weather is over. Both fertilizers are rather instant and not a time-release formula. I have 12 month general and manganese fertilizer spikes for palms (in the corners of my fescue lawn) and 12 month citrus spikes around my lemon tree. The other planters get some of the 15-15-15 about 3 times a year (late October, March, July).

I’m open to further suggestions, and appreciate everyone’s feedback and input.

  • Garrett


@grit thanks for reaching out. I reviewed your account and have a few recommendations:

Just to clarify, these are all setup to water as individual zones, correct?

This is a good hypothesis. We use default root zone depths for cool and warm season grasses which might need to be adjusted for your grass type and pre-Iro watering habits.

After doing some digging on Marathon tall fescue, it appears that it’s recommended to be watering 2 to 3 times per week at 80% ETo Optimum, 60% ETo Minimum, which would equal 20% to 40% MAD. I’d recommend setting your MAD to 40% and ensuring the root zone depth (for all zones) matches that of your actual lawn. It’s simple to test using a soil probe if you’re not sure.

If possible, after adjusting your root zone depth and MAD, let’s try to let the system run for a week without making any adjustments. This is the only way to see what the system will do with the weather data it’s receiving.

We wear shorts all winter in Colorado :wink:

Let me know if you have any other questions we can help with. The above link has a number of maintenance tips related to mowing, fertilization, etc as well.

Hope this helps.