What has changed? Did a tree grow and create more shade? Have you fertilized/not fertilized them differently? Do the plants themselves look healthy and full? Grasses sometimes need some nitrogen fertilizer so a soil test should help you see if you need to feed them.

Stress the plants. Play mother nature and send a little signal in the middle of summer by holding off some water and maybe increasing just slightly the phosphorous in your fertilizer for flower and seed formation.

I have had my pampas grass for about 4 years now and never have they plumed. I recently (early march) moved them to full sun. I hope to get some plumes this year but I'm wondering if I need to fertilize them. Has anyone ever tried epsom's salts?

Generally, fertilizing ornamental grasses is not necessary or even recommended - fertilizing has a tendency to produce lush growth (at the expense of flowering) that becomes rather loose and floppy. And I'm not sure what benefit empsom salts would provide unless your soils were radically deficient in magnesium. Lack of pluming or blooming is usually related to insufficient sun conditions or lack of summer heat or, too much fertilizing with a high nitrogen content.

gardengal48 thanks for your reply. i will wait impatiently to see if the full sun helps and i will not
fertilize. so far it's growing fast and full.