Looks like a watering issue, as in too much as some point.

Culinary sage is a drought tolerant Mediterranean plant and isn't happy with soil that is too wet for too long. Even in a pot, the plant should be allowed to dry out a little between waterings. The rain may have added to the problem.

By the way, I don't think Salvia officinalis gets mildew.

Joe

Thanks for your help, Joe. I have stopped watering it. (And: Yes, unfortunaltely Salvia officinalis does get powdery mildew. Iv'e lost one to it some years ago.)

Joe is right!
You need to repot into a grittier soil mix-try commercial
cactus mix which you can mix at 50-50 with coarse sand or
a fine grade of gravel.
the plant also enjoys full sun all day.
Salvia is a heat loving plant and will enjoy your warmest,
sunniest driest spot on your porch or in your yard.
I,too, love this genus and have a Salvia apiana which I
have in a clay pot with a soil mix of
1 part of this mix:
commercial potting soil: 5 parts
supersoil soil conditioner: 5 parts
fine ground cover bank: 5 parts
perlite: 3 parts
then combine 1 part of above mix with 1 part of pumice
to make the final mix for the sage.
on the bottom of the clay pot I use a piece of screening
to cover the drain hole
then cover with 1/4-1/2 inch pea gravel
then fill in with above mix, set on the salvia, and fill in
with more mix.
I have my plant in the sunniest spot I can find that is easy
to get to to water (on the roof!) it gets some late afternoon shade. the plant leaves will appear to be closing
up when it gets too dry but with the above mix I can water every other day or twice a week as the leaves indicate that it is dry.
It is better to let the plant dry to the wilting point than
overwater.
Click here to read about Salvia

Thanks for the soil recipe. There will be some serious re-potting action on my back yard this weekend...
Terrestrial Man: Have you actually tried out the cactus mix?

I too am having a similar problem with my sage, the leaves are curling as shown in the photos above, however they are not turning brown or dieing they are just curling like horseshoes. It started happening when I re-poted it into more organic soil than what it was in, at first I thought I might have over watered it so I let it sit for almost two weeks before watering again but symptoms continued. It currently is under a 400HSP grow light so it gets plenty of light along wiht several other herbs that are growing for cooking. I think from the observed conversations that took place above that I might try the re-poting once again into cactus mixture and see what happens. Any thoughts? Can I leave it in the organic or will it be unhappy? Any feedback would be appreciated

-Chris_