It is certainly not recommended but if you don't care if the grass survives the winter and returns next spring, go ahead.

Ornamental grasses come in both cool season and warm season varieties. Cool season grasses emerge very early in spring, grow rapidly and flower early. Warm season grasses are much slower to emerge, develop during the heat of summer and then flower in late summer to early fall. Pennisetums - and most other popular OG species - are warm season grasses. And they are not even recommended to be planted in fall, let alone divided. The reason for this is that once they start to flower in late summer, the roots begin to go dormant and stop growth. Without active root growth and development, cold and wet winter soils will generally result in the death of the plant.

Division and planting of warm season OG's is advised to be done in spring to early summer. This is why warm season OG's are typically offered at a discount or sale prices late in the season. But if you don't care about winter survivability, feel free to go ahead and do what you want.

Thank you so much for this reply! It is super helpful and something I did not know.

I found that information helpful as well, GG. I seem to have it in my head that Fall is always the best time for me to divide and replant across the board, so I learned something new today.

I got lucky that I did divide my Pennisetum 'Hamelin's and another variety that I forget the name of, last spring. They really did take off and grow fast and they are all doing great now having formed a new circle of a grass with a lot of blooms on them. We had a lot of rain and they loved that. They never looked better.