Ask Mr. Smarty Plants

Without knowing exactly under what conditions your Nassella tenuissima (Mexican feathergrass) is growing, it's hard to say. Here is what our Native Plant Database page on this plant has to say:

"Growing Conditions

Water Use: Low
Light Requirement: Sun , Part Shade
Soil Moisture: Moist , Dry
Soil Description: Well-drained, acid or calcareous sands, loams, or clays.
Conditions Comments: Requires good drainage and cant take excessive moisture. Should not be watered heavily more than once a week. Goes dormant during drought and in winter. May rot under heavy mulch. Grows well in containers."

You will note that it goes dormant during drought and in winter. Until it finally started raining last week, this summer has been very dry. How long have they been planted? If they are recently planted, perhaps they were planted when it was too hot, or do not have good drainage in their beds. If water stands for a while on the ground when you water, it is a sign that clay soil underneath is not draining well, and this plant cannot tolerate water standing on its roots. If the grasses are in a sprinkler system area, and getting more than the once a week watering, that could be a problem. It also doesn't like heavy mulch. We would suggest that you trim down the grasses to about 6", pretending that it is winter. This will take some stress off the plant, so it is not trying to get water up to higher portions of the plant. Then, only water them once a week, and not that if there has been regular rain. Let the water dribble into the plant area from a hose, and don't water them from an overhead sprinkler system if you can avoid it. Notice in the pictures below that the feathergrasses have various positions of "standing up," with some portions of the plant on the ground and/or turning brown.

From our Native Plant Image Gallery:

Nassella tenuissima

Nassella tenuissima

Nassella tenuissima