Sun scorch, maybe? Your compost looks fairly rich, did you mix in lots of grit to make sure it’s poorer and free-draining? Otherwise it might retain too much water and both that and a rich compost will make salvias grow soft and more susceptible.
Edited to say it looks as if the foliage is wet, has it been sunny after? Sun on wet leaves can intensify scorching even if everything else is right.
Mountainous Northern Catalunya, Spain. Hot summers, cold winters.
Salvias don’t usually need feeding, all mine are in the ground and the most they get is a bit of fresh mulch every other year when I’m topping up the raised beds. I’ve never grown a salvia in a pot though, where the compost will eventually be exhausted of nutrients. Hopefully someone who does will chip in..
Mountainous Northern Catalunya, Spain. Hot summers, cold winters.
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No grit, just compost, but I have been feeding them, am I not supposed to?