Rent a good gasoline powered hedge trimmer. It's like a chain saw motor with a hedge trimmer blade. A good quality (Echo) 20-24" trimmer will make fast work of any grass, but unless you have lots of grasses and hedges to trim, you probably can't justify the $300+ cost of purchase.

There are other, multi-use tools which can include a trimmer blade, which may be easier to justify owning, as you can use them for more than one task.

I've been able to cut my large miscanthus clumps with an electric hedge trimmer. I just work around the outer edge, removing canes as I cut toward the center. Sharp blade is key...and keep the cord out of the way!

Here is a link that might be useful: Cutting Back Ornamental Grasses

I'd like to thank both donn and grass guy for their suggestions. My wife and I were able to cut down our grasses with an electric hedge trimmer. This worked very well. We used a bungee cord to tie up the grasses and hold them together then used the trimmer at the base. Took some time to cut down the largest grasses but it worked!

Thanks again for the great idea.

Now that you've cut them back, be sure to clean the crown of debris that can cause rot. Rake through with a stiff metal rake.

Sounds like you managed to avoid the cord while trimming...I won't go into why I mention that...:)

I know your done with this task, but.........I use my electic chain saw on them, the bungee cord works really good to keep them in a nice thigt bunch doesn't it?