"pam" wrote :

Generally, yellowing foliage on Perovskia indicates TOO much
water. This is a very droughty plant and requires little if
any irrigation after establishment. I am surprised that
planting on a slope is creating this effect - typically sloped
plantings have very good drainage. Are you watering it often?
If so, I'd cut back a bit and let things dry out.

Not that much but there's a water ditch behind in so it is moist. I
guess as it establishes rooting, it might get better.

I thought it might need iron because of the clay soil but they grow
all over town just fine.