I'd say 8-10' and it will flower but not produce seed. After your first hard frost, cut it to the ground, and unless you are certain to have good winter-long snow cover, mulch it heavily.

Many thanks donn!
CMK

Donn, why do you advise cutting back after the first hard frost???? Why not leave it standing thru the winter?

I have lost plants of Arundo by cutting them back in the late fall or winter. Opening up the large hollow culms seems to allow water to get down into the crown, add freezing temps and you get mush.
A.

Hi A.

I doubt if the plants were killed from water in the culm stumps. You'll get water in the stumps no matter when you cut the plant back.

I cut mine back whenever the temperatures kill the above-ground plant, because they don't seem to be able to remain standing through the winter. After they've died back, the first strong windstorm or heavy snowstorm flattens them.

Not water alone .... But, when cut back short enough when that water freezes (at -30C) it does seem to do damage. I do trim back the stems that are weak but, I leave at least a foot until I trim them all back in the spring.
I must grow mine a bit 'leaner' as most of the culms stand up throughout all our heavy snow falls AND even the snow that come crashing down off our metal roof - amazing!
I am still impressed that Arundo is surviving our low winter temperatures and still achieving 8-9 feet of growth in a season. (note: the plant I am referring to is the plain green - not the variegated. I must try a variegated variety up here one of these days)

I am in north central Kansas. Zone 6 formerly zone 5. This one gets about 8' tall here, flowers and stands upright through the winter. Love this plant. I bought Peppermint Stick this year and hope the foliage keeps its variegation all summer like they say it does.

Forgot to add that I cut it down in the spring

'Peppermint Stick' is the only cultivar I'm currently growing, and it definitely keeps its colors all summer long. It fascinates my neighbors. One of them asked if it was ornamental corn.

This is why you check 'notify me by email' when posting before you forget, lol.

Wonderful pic sandalwood. Wish I had found that 'Peppermint Stick' instead of the plain 'Variegata'- the variegation on yours is a lot more prominent.

-donn, "growing, and it definitely keeps its colors all summer long."

So do you find Variegata 'greens out' during the summer?
CMK

Didn't explain myself very well. My picture is of Variegata in very early summer. It has greened out now. I have several starts of Peppermint Stick (new this year) and it is still holding it's white so far.

Thanks sandalwood. That's a bummer Variegata greens out completely. If it does well and comes back next year I may have to consider swapping it out with one of those Peppermint Sticks...
CMK