Red lava rocks cause excessive heat on roots, which are normally stay cool with normal mulch. The high, excessive heating of roots will stress most plants.

Thank you Yard, I know about the rock, the planter is huge,and I cannot afford to remove and replace it. I have had these plants here for over 4 years, they even survived the insane heat and drought last year. This damage is new this year. And just on these plants. Everything else is healthy.

Just wish I knew what it was causing this.