Hello,
Growing outside is challenging. It can have many struggles.
These red colored leaves look like a few possibilities.
1) ph is very high, being the 7.5, you can add sphagnum peat moss or a granular sulfur to the soil to fix this naturally.
2) can you cover plant with blanket for those cold nights?
3) the soil looks a bit wet...if its staying muddy there's not enough air and it isn't drying fast enough. You could use vermiculite, perilite, the sphagnum peat moss can help too, or other things to break up the space of the soil. I think you can poke holes around the plant and slowly add these things in versus having to dig up the plant and fix the soil.
I hope this helps some. Enjoy the season, happy growing.