Stripped Threads: I have used dethatching blades on my lawnmowers for more than 20 years. When you buy a brand new dethathcing blade, they come with adapters that assure centering on the 2 different blade mounting hubs I have on my 2 different Snapper blade mounts. Among the things you have to do is have a fairly flat lawn, wear long pants, eye protection, and develop a feel for the speed you run at. Up until last year, I ran my dethatching blade alone on my 20+ year old aluminum deck Snapper with the original Briggs Classic 3.5hp engine using the side discharge chute. Last year I started using the Snapper with the high lift cutting blade installed and the dethatching blade installed on the bottom of the cutting blade. My dethatching blade has bracing holes that normally fit on the newer white metal shear pin types of blade mounts. I install bolts through those holes and position the dethatching blade so that the bolts shoulder up against the cutting blade so the dethatching blade does not spin on the mounting shaft. I also use a bagging attachment which saves me one more step and the system works great for me. Some things that will help: Wear a dust mask if the ground you are working on is dry. If you are going over new ground that may have pebbles or other hard or sharp objects in it, be sure the deflector the lawnmower should have on the back of it is on and wear high top shoes or shin guards. The safety glasses are for ricochets and I wear them and ear muffs even for regular mowing with regular blades. I live on a corner lot in the city and the springs last for one job so I always buy new springs for the next year. If you try to save the $5 for new springs by lowering the mower so that they can do the job, you will not like the results so spend the $5 per year. My Snapper is self-propelled and I use it at the slowest speed and am happy with the results. If you use a push mower or one that goes too fast at its slowest setting, you will have to figure out your own method for a good dethatching job. With the blade properly centered and if you don't have bumps in your yard that would jam a regular blade, you won't jam the dethatching blade either. The flex of the spring that does the actual dethatching keeps the engine from being excessively stressed, but does tax it a little more than just cutting grass. I HAVE NOT lost an engine yet to my dethacher, but in my younger days have bent crankshafts with regular blades because I used to scalp my lawns. Everything I cut now is 3+" inches high so that even frost heave mounds can not hurt the mower. The dethatching blade WILL NOT do as good a job as a POWER RAKE, but the convenience, low yearly cost, availability, and self-propelled bagging features of my Snapper makes the dethatching blade more practical for me. Fairyprincess

Since you say the soil seems compacted, I think I'd go for the aeration rather than the dethatching. It won't get rid of all the thatch, but it will poke holes in it and help the decomposition process. If you're mulch mowing, that should help get rid of the thatch, as well. There are some warm season grasses where mulch mowing can contribute to thatch, but since Marathon is a fescue, mulch mowing will help the thatch decompose. Over fertilizing and frequent shallow watering are the two biggest contributors to thatch, so if you're watering deeply and infrequently and fertilizing appropriately (especially with organic fertilizers), I think the thatch will start to go away on its own.

You can dethatch in July, but that doesn't mean you should. Grass is already stressed in July due to the climate and dethatching stresses it further. You're better off dethatching in cooler weather, either spring or fall. You want to do it while the grass is growing, so it can recuperate, but it should not be when it is too hot and dry.

If thatch is just the accumulation of dried clippings they can actually provide cover for seed that works is way into it. If thatch is the watertight web of dead roots and stems the new roots will not penetrate very well. Dethatcher is a good idea so you know the seed makes contact with the ground.