Sounds like you've built yourself a bit of a nightmare. I'd recommend a gas trimmer.

"Is that string more damaging to grass than mower blades?"

It doesn't sound like "damaging" the grass is the problem:)

Were you vacationing in Cancun, when the grass was growing, this spring? Or skipping the "light fantastic" every day at some gambling resort, instead of staying home to mow the grass?
And, grass is, i have to admit, a living entity, but it has to be mowed every week, or oftener to keep it under control!
I was going to suggest hand clippers, but you seem to be sort of fed up with that slow process! And, trying to use a push mower, or a riding mower, in that jungle you have developed, would be akin to self-imposed suicide!
Or, you could end up looking like the Stephen King character, who ended up with grass growing on him! Of course, if that happened, you could get some goats to munch away until you looked human again!
So, yes, i think a gasoline powered string trimmer will be the way to get out of the "fix" you are in! That, plus lots of work! And, buy several rolls of trimmer string!
There is another way, which might be called a "last resort!" Buy a couple gallons of Round-up, and a large powered sprayer, and get to it! Oh, yes, the grass will be mad, but at this time, its beyond hope anyway!
And next spring, plant new grass, and mow it when its time! Or hire some kid to mow it while you are frittering away the spring weather, at some nice resort!

Get a string trimmer and a good walk behind mower. Cut what you can down to a reasonable height with the trimmer and use the mower to put a nice even cut on areas you can get to.
If you cannot do this much work hire it cleaned out the first time then maintain it yourself. Don't let it get so far out of control.

It isn't regular grass, but expensive ecolawn aka fleur-de-lawn, a combination of dwarf perennial rye, strawberry clover, and broadleaf miniature evergreens and flowers. It is advertised as needing no mowing. The fleur-de-lawn itself only gets to about 6"; it was the weed grasses poking through that grew really tall. And I work in the yard all day every day, but have had to spend most of that watering the 300+ trees fairly newly planted, and weeding, and couldn't keep up with all the fast-growing grasses.

Got lots of advice that trimmers were too dangerous and liable to cut into bushes and trees so won't buy a trimmer. No way to use a normal lawn mower in here. Apparently there are grass-cutting tools that use a grass blade instead of string that might be best. Will look and compare.

I had my yard helper liberate the flagstones and baby bushes and I've been maintaining that with hand shears so although it's time-consuming on hands and knees it's working for the moment until I find a safe tool.

Have a severe water run-off problem here in winter so had to use erosion control grass / clover to bind earth so it wasn't avalanching out of yard daily. This thick lush green cover provides protection to the baby bushes and trees against the fierce burning sun and helps with moisture retention. Eventually the redwoods, sequoias, sweetgums, willows, maples, etc -- huge trees-to-be, will shade out the grass, but by that time the tree roots will bind the earth and the trees will shade their own roots.

Thanks for all the advice. It's not easy establishing a forest from scratch in weed-infested waterlogged yard, but this experiment is gradually taking shape and actually now, even though in baby stage, is very beautiful already. Doing a time-warp forest succession plan, with biggest problem getting enough shade for saplings to survive. As soon as it gets blazing hot with burning sun July 4, that grass will be a godsend!

Hello all.

Hi cascadians. This just might be the tool for maintaining that fleur-de-lawn.

Good day.

Here is a link that might be useful: This is not a normal lawn mower.