Pennisetums don't usually need to be divided very often, unless you want more plants by division. They don't die out in the middle like Miscanthus...and don't generally increase in width to a large degree.

Scotty I am so glad to get your answer and even more happy I will not have to divide a lot. Thanks so much for taking the time to answer my question.

Mine go years. I think 'Little Bunny' was 6 before I divided her the first time.