You can mow the new grass when it gets up to 5 inches. Then mow it down to 4 inches with the rest of the lawn.

I'd wait and mow when it's dry.

I strongly disagree with letting new grass get to 5 inches. The companies that produce seeds recommend that you mow newly seeded grass when it gets to 3 inches, cutting it down to 2. It will promote tillering and maturation and it will prevent it from laying down on itself. Personally I wouldn't let mature grass grow to 5 inches either, nor would most, if not all, major universities with a turfgrass program.

I'm not going to try to convince you that the following picture is what you should strive for, but this is what the fescue looks like at my university...which offers a bachelor of science degree in ornamental horticulture.

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It is grown on many of the embankments as a ground cover where mowing is impractical and to resist erosion.

The following lawn, which has always looked to me like KBG, is claimed by the owner to be fescue. It was being mowed at 4 inches.

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That lawn belongs to GW member, William, and was posted here in 2005. William's reason for posting it was to thank us for the advice to raise his mowing height all the way to the highest mower setting.

Dchall and I will never agree on mowing heights, but I stand by my post. To advise people to wait till their new grass is 5 inches isn't correct. For a mature lawn, you can cut as high as you want as it's your lawn, but personally I think it's too high. As an aside, ornamental horticulture is not the same as turfgrass science.

Good points. The specifics of my approach are often at odds with others. The ultimate answer to the question is you can mow new grass when it is tall enough to be mowed. But your mowing height for cool season grasses is not 1 inch like bermuda. It is much higher.

The hairy looking grassy hillsides at my school are ornamental ground covers and not meant to be walked on like a normal turf.

Hey grass1950. Welcome to the discussion. The idea of tall grass does not come out of academia or even the professional turf studies. It comes from experience on the forums which include the forums for lawn professionals. The most intense study of actual lawns is on the lawn professionals forums. Some of those people are highly focused. It seems there is always a discussion about what is the right height for certain grasses. In my opinion the consensus is there is no consensus. The pros who are motivated by quick money opt to mow low. The short canopy allows weeds to come in which gives them an opportunity to sell a separate weed treatment. The pros who pride themselves on appearance go with (1) full control of the sprinkler system from the homeowner, (2) mowing high for most lawns (except bermuda, centipede, and bent), and (3) three chemical fertilizer apps per year (1 in spring after the spring flush of new growth and 2 in the fall to "winterize.") Most all pros will mow on the 7-day schedule regardless of how the grass is growing. They like that weekly check. The 1/3 rule is more of a guideline.

I am experimenting with tall grass. Of course I am not a university, so this is an considered an anecdote in the academic world. My peer review comes from my peers on these forums. I have seen St Augustine growing tall in two locations. One was my neighbor next door about 5 years ago. She was in the house for 5 years and never once mowed or watered. Her grass always looked better than mine which I was mowing, watering, and fertilizing regularly. Her lawn was in fairly deep shade most of the day. It grew up to around 12 inches high. The other location I have seen tall St Augustine is adjacent to the dog walk at a condominium in Port Aransas, TX. The St Aug had escaped out into the sand dunes. That grass was never watered, mowed, or fertilized for about 15 years. It grew up to about 30 inches high in full sun. That grass always looked pale green but it never suffered from any of the droughts we get in Texas...until last year. It will be interesting to see it again this year because last winter it looked dead.

My personal experiment looked like this in February...

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All the other lawns in the neighborhood were dormant as was part of my lawn that had been mowed back 5 months earlier.

As of last week my lawn looks like this...

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I know. Tee hee hee! Hey Marge! Get a look at this guy's lawn? Well look again. The grass where she is sitting has not been watered or mowed since October. I bought the house in mid September. Lawn has not been fertilized in years. The previous owner bought the house from an estate and did nothing. Estate did nothing and the former owner did nothing in her later years. The guy I bought it from had been renting the house and ignoring the lawn. He kept it mowed for two weeks while we were closing the deal. This part of the lawn has no weeds, no disease, and looks pretty darned green for getting zero care. The areas that were mowed are not doing as well. I also have issues in the areas on both sides of the house where I get runoff from the roof during rain. I am hoping this really tall grass will move into the areas where bermuda is creeping back in. The location of this experiment is George West, TX. Our temps are just getting into the low 90s. Normally we get a coastal breeze bringing heat and moderate humidity but we are much more arid than either Corpus Christi or even San Antonio. If we get wind from any direction other than the sea breeze, then the humidity drops into the 20s or 30s and desiccates the soil. That range of humidity is part of this experiment. The area in the second picture above looked very dry last weekend after a wind shift, but then the winds turned back from the coast. As of Friday it seemed to have recuperated without irrigation.

What I'm trying to do is to advance the understanding of tall grass. I am hoping someone else will see these images and try an experiment with theirs. For someone who might be interested in such an experiment, it is helpful that my wife does not live at this house and the lawn is 100 feet back away from the street and neighbors.

Thanks for the weclome dchall. All I can say is "to each, his own." Up here in the N.E., my HOA would fine me if my grass was as high as ann elephant's eye. The consensus I was refering to was that posted by university extensions. For those that do cut, the 1/3 rule is a wise one to follow--cut too much and all that is left is the stem. And no, I don't take everyhing that comes out of acedemia as gospel and I agree with you about many "professional" landscapers.