Root depth


What is the opinion of others regarding root depth settings? We have new sod as of late last fall. I would judge the initial root depth to be 2", if even that. This is where it is presently set. Over the course on the summer, should I increase the depth setting, and by how much and when?


I’m curious about this too… I moved into a new home that already had sod down last Fall. I’ve been running the root depth at 9(default), not even thinking about it until this past weekend.

I’ve considered getting a soil probe from Amazon to do it. I guess you could use it to check several different areas in a zone to get an average. However, I don’t know how much it would mess up the grass growing in a particular zone or if that even matters.


Looked on Amazon, and soil probes are expensive! I have a manual aerator, foot operated. That may do the job. Only need a depth of 4-6" or so, not what Amazon has for sale going to greater depths.



What type of grass is the sod made up of?


Not a grass expert, by any means, but as I understand it, primarily Bluegrass. Was sodded as the weather cooled, and coming to life now. We are in Rexburg, ID with relatively long/cold winters.


Typically with that type of cool season grass, the roots will be anywhere from 2-6". If the soil is primarily clay anticipate the roots to coincide with the shorter end of the spectrum. In addition, in compact soils, the roots will remain at a shorter depth because there are low levels of moisture and oxygen deeper in the soil.

Setting up an “as needed schedule” with the root depth of 2" is a great starting point. The roots are going to do most of their growing during the Spring, after which they won’t experience much growth for the remainder of the year. That being said you won’t have to worry about constantly switching depth levels as the year goes on.

Start with 2" and monitor the lawn during the Spring, if it looks healthy then it’s safe to say you choose the right root depth, which should give you a healthy lawn all year. If you decide to switch depths then make the choice based off of your soil type, the rule of thumb being, denser soil, less root growth.

Lawn turning brown

Thanks George! At 2’ now, and will possibly go to 3" in a couple of months. I would term our soil a clay/loam. I’m doing a Flex schedule and loving it. Also, as I understand it from bits and pieces gathered from the forum, one can dynamically change the root depth with Flex and it will adjust, but not with As Needed. However, need a firm ruling on this if you have knowledge?


Great question and I hope this provides a little clarity.

Root zone depth will affect flex immediately, with water as needed it would be reflected in frequency for the current month of watering (if you’ve changed it enough), and frequency and duration when it is adjusted at the top of the month.


How would I guesstimate my root depth? My Bermuda with clay soil in Georgia is almost two years old. Any ideas what my estimate would be?


Go 6 inches. If you properly maintain you turf 6 inches is pretty easy to obtain.

Mine is at 8 inches but I use growth regulator which has a side effect of deeper roots.

If you want to measure it yourself, do what I do, take a plug of soil, soak it in water and slowly massage away the clay, you will be left with the rhizome with the root hanging off. Measure the root while it is wet.


Thanks for the help! I’m guessing you are in the same situation as I am with geographic region and soil type, so do you mind if I ask what your other settings are? What did you decide for available water, depletion, and crop coefficient?

Thanks again!


I have mad at 50% on some turf and 70% on a few and my soil is set to clay in some zones but Loam clay in others with available at .1 on all. Dang, co is default warm season grass of 65.

but for now just set mad to 50 available water to .1 on a flex schedule if you want to fire and forget. If you want to play around then you need to measure your roots and adjust accordingly. If you don’t want to measure your roots, step up your mad 5% per watering until you see heat stress. But keep in mind our August, it’s very dry so I have no success going over 70.

The idea is that you want the water to drop below the wilt point so the grass will burn carbs stretching the root, but if it doesnt reach water (I think .16 -.25 inch), the rhizome will begin dormancy. Some call it training.

I’m assuming you feed and now properly, else you might want to move your available water back to .25


Does crop coefficient (set by the user) impact flex schedules yet?




I ask because this wan’t exposed via the app pre-2.5 so it couldn’t be set. And 2.5 wasn’t a Flex release so was wondering if they modified Flex to take advantage of the setting.


well let’s wait for @franz to chime in but i can’t imagine they would overly complicate their code in this manner by providing 2 sources for the same data.


But unless you have gone through the rigorous process of calculating it yourself, I don’t believe this is a value to modify to augment your watering. Unless you have a non common vegetation. For the grass it’s pretty damned close and by changing it 5% you are going to increase or decrease the watering threshold by less than and hour, which doesn’t seem to buy you a lot since the schedule can only run 1 time a day and is verified/recomputed every 24 hours.

I’m not saying you shouldn’t change this, just have a very explicit reason to do so


Ok, so My mad was already 50% so I left it, and I changed the root depth to 6 instead of 9. Immediately I see my flex schedule drop from 56 minutes per zone to only 36 minutes does this make sense? Also since my sprinks ran yesterday it is now showing 104% moisture level for each zone, including the drip zone which is on another schedule! Not sure why.

Yes I do mow frequently, no reel mower yet but I’m as low as I can get without scalping to dirt with my rotary. No leveling done yet. I put down 3.2 lbs per 1000 of N a week and a half ago, and I occasionally treat with Celsius in between my applications of prodiamine as well.

I figured I would list everything I do to display that I am somewhere in between a homeowner and an expert. Irrigation Is now something I’m trying to figure out but the rest of it I’ve become pretty familiar with.


@johnny2678 @plainsane Regarding Flex and crop coefficient, I hope to be using the user defined zone crop coefficient by next week in flex, I’ll post before making the transition.


The watering time adjustment is normal behavior. Is 30 minutes right? I can’t tell ya that, don’t worry about the moisture level.

With the more shallow root zone the irrigation time reduces because you need less water to saturate a smaller soil column