The plant is three years old and it is in a good drainage area. It is slowly growing and has never made any plumes. My sister-in-law bought it for me at the same time she bought one for herself. Her plant is much bigger than mine and has plumed the last two years. She has an automatic watering system and we thought that might be the difference, but I have been watering mine every day too, so I do not know what is wrong.
Why Is My Pampas Grass Not Making Plumes?
Certified GKH Gardening Expert
If your grass is not making plumes, it is likely either too much nitrogen or too little phosphorous. This is caused typically by ornamental grass that is planted close to a lawn that is well fertilized. Lawn fertilizer is is high in nitrogen, which inhibits flower (or for ornamental grass - plume) development.
Both sides, either too much nitrogen or too little phosphorous, can be corrected with some high phosphorous fertilizer for the plant. Bone meal is a good fertilizer in this case. Try adding some to the plant and that should correct it.