If soil temperature is the most important factor - and research seems to indicate so - then the hypothesis should be easy to test by obtaining weekly average soil temps over say the last 10 years, graph it and see where the periods of ideal temperature for root growth are. I will try obtain that information.

I have been working on obtaining information in regards to soil organic matter. One of the professors at the University of Georgia, also an extension specialist on forage crops was able to provide me with a wealth of information on the matter including studies. It's groundbreaking information that may change the standard narrative in regards to OM. Stay tuned, once I get his permission to release the materials I will make them available for review and comment.

Another interesting item - if root growth depends on or correlates to blade/shoot height, then mowing shorter in the Fall/Winter for overseeding and/or prep for winter is impacting root development/regrowth.

@newtolawncare

It is not just cut height, but frequency. If you do it once the impact is likely to be negligible.

Here's a very interesting experiment that was done on fescue to show the impact of proper grazing management. Both boxes started with 3 foot roots (!!!), one was cu to 4" every 30 days, the other to 2" every 5-7 days. The impact on the roots is dramatic.

http://www.gaininggroundvirginia.org/resources-index/demonstrations/

With lawns, it would have to be tested but I expect we are closer to to the 2" every 5-7 days , though the frequency and cut height is a little different - 3.5" every 4-7 days depending on season. This may effectively put an upper limit on how deep the roots can go in your average fescue lawn. If we could live with waiting 2 weeks in between cuts that would probably double to root depth of the average lawn.

Something to think about, especially in areas with water availability issues - letting the grass grow tall may greatly reduce the amount of water needed to keep the lawn alive due to it tapping into deeper water.

I wonder how deep the roots went on my 32-inch tall St Augustine...(That's my chow chow's tail and ears as she walked through the grass)

According to this , St. Augustine roots will go as deep as ~2 feet, though mowing practices are not mentioned in the summary. $30 will probably get you that information :-)

Looks like you could feed about 30 rabbits with what you got there. If they will eat St. Augustine. How's that for sustainable, let the grass grow for 2-3 weeks, get deep roots, use less water, raise some rabbits too - fresh organic meat year round.

My local rabbits taste the wrath of my BB guns quite regularly, but I don't think I'd eat them.... Besides a BB doesn't really kill anything. They give me scornful looks though. I'm intrigued by 3/8" golf course Bermuda with roots 12" deep--How do they do that!!!???