repetition is key

 Before

After

It's something that I usually have to say at least twice. Never once, and frequently three or four times.
The conversation goes something like this:

Friend: How far down should I cut my grasses?
Me: Down to the ground.
Friend stares blankly. Three second pause.
(Wait for it)
Friend: Down to the ground? (eyes wide)

Me: yes
Friend: Down to the ground?

I've learned that "yes" usually is unacceptable, and Friend continues to ask the question until the words actually come spewing out of my mouth at least one more time.

Me: yes, down to the ground!
Friend: Really?
Me: YES, DOWN TO THE GROUND (If I'm feeling really snarky, I add, "You know, the part also known as earth or soil?")

Inevitably, there is commentary.
(Wait for it)

Friend: But...is that okay?
Me: Yes (duh!)
Friend: really?
Me: Yes.
Friend: But I don't see other people doing it that way.
Me: Sigh.

 After

If you observe how most ornamental grasses grow (exceptions are evergreen grasses and bamboo), they grow from ground level, not from the top of the flower stems that bloomed last year. Landscapers and many people trim their ornamental grasses down to about 2 feet, sometimes making a shaving brush shape of the thatch. That's perfectly fine if you like that look. It leaves something to look at, and tells the landscapers that something intentional is planted there, and that the green stuff growing up later is not a weed.

But that mound of thatch remains through the growing season and is visible.  It does not grow, and it leaves a congested area through which the new leaves have to grow, usually spindly from the struggle for light. The plant looks like a pincushion to me, throughout the season, with the dense sheared bottom and scattered leaves poking out the top. It isn't long before the thatch is too thick, and the center dies out, creating a green ruff around the sheared brown (not that I have anything against male pattern baldness, but a grass shouldn't look like this. It should look like this - below).

After 

Since the new leaves grow from the roots, just cut the dead stuff down to the ground, just like you do with other perennials that regrow from the roots. You wouldn't leave all the dead growth from the previous year on an Echinacea, would you?

Other than preventing the landscapers from pulling the plants out, leaving a tall thatch on ornamental grasses does have one other benefit, though. It keeps the rabbits from eating the new growth. So when the rabbits come back to Casa Coniglio, you might see me leaving thatch on my grasses.

 After (can you see the thatch? No!)