In the corner of my garden grows a large Pampas Grass. I do not know the variety but it has large white showy plumage in Autumn. My problem is the last couple of years 10 or maybe 12 beautiful plumes appear around 10ft. high. After a couple of weeks the plumes break off the thick and robust stems, while in other gardens around my area they last all winter. Last year we had some high winds, so I put it down to that. This year before the plumes came out, I tied a very loose rope ring around them so they would not sway too much. Although we have had no strong winds to date, half of the plumes have broken off and I fear for the rest. The plant looks very healthy all year round and I have never cut it back. Three years ago I planted a so called pink grass, one at either side, thinking it would look good, but the new plumes were not pink but grey. However the three grasses have now grown tightly together and joined each other in a tangled web. Could this be the reason? Hope you can help.
It sounds to me like you may have a pH issue in the area. I would say this would be a deficiency if it were grown in container, but in the ground the grass will have more than enough nutrients to go around. To control the pH of the soil, I would recommend adding dolomitic lime. You can just spread it around the top. If that doesn't help any, you can try adding potassium silicate. This can help sturdy things up a bit also.