The fescue grass in my yard is not doing well. I suspect that I may be cutting it too short--especially in the summer heat. I have cut it to a length of three inches for several years now. How tall should fescue grass be before and after cutting?
Taking into account the below couple of questions you've asked here on SE:
Q. Is a cool-season lawn "Fescue" the right type of lawn for your location?
See here: Selecting a Lawn Grass via South Carolina - Clemson University Cooperative Extension
Growing grass in a shady location, especially one shaded by tress, is going to be difficult. Period. Why?
Grass doesn't grow well in shady areas, even varieties developed for such areas require a lot! more work than grass grown in sunny locations.
The root system of the grass simply can't compete with the trees root systems.
See here: Growing Grass in Shade via South Carolina - Clemson University Cooperative Extension
Below quoted information comes via, What's an organic way to discourage crabgrass from a large “lawn”?
Mow high and when doing so only remove approximately ⅓ of the grass blade height. In my case, 3inch (75mm) is my final cut height, that is as high as my current lawnmower will cut. My next lawnmower will be able to cut to at least 4inch (100mm).
Seeing as my lawnmower is a mulching mowing, I leave all the grass clippings on the lawn (free, natural fertilizer), except with first cut and last cut of the season. I collect up those cuttings and dispose of them via a community yard waste pile.
During dry, hot spells (generally July & August here in Missouri), when temperatures are constantly over 90°F (32°C) I never go out and cut the lawn. A cool-season lawn hardly puts on any new growth in those kind of temperatures (will start to enter dormancy). Once the temperatures have dropped back into the 80's°F (mid to high 20's°C) for a few days, I will go out and cut the lawn, but only if it needs a cut. If it doesn't, I just wait until it does and temperatures are right for cool-season lawn cutting.
You may want to take the time to read the complete answer, as all the information within is based on a "Tall Fescue" lawn.
If cutting to a final cut height of 3inches (75mm) hasn't been working for you, try raising the final cut height to 3½ to 4inches (87.5 to 100mm).
You may also wish to have a browse through the following information from, South Carolina - Clemson University Cooperative Extension: