Can I cut the plumes? If so, at what time of the growing season? If I can cut the plumes, how do I prepare them for display indoors (hang upside down until dry? Keep in a vase full of water?)
Certified GKH Gardening Expert
The best time to prune this is in late winter, or early spring right before the new growth shoots up. By this point they will already be dry and ready for use. If you do want to cut a few off then you may do so, but they will not look like they do when they are already fully dry. They won't fill out exactly as you want them to.
Here is an article for more information: https://www.gardeningknowhow.com/ornamental/foliage/pampas-grass/pruning-pampas-grass.htm