"Northwest corner" ... "all get watered the same amount" ...

I take it you have a block wall around your property? It could be the reflected heat coming off the east- and south-facing walls. Are the plants that are doing well further away from the wall(s)? If so, try giving your NW corner plants more water than you give the others.

I've noticed the lawn along my wall always needs more watering, due to the reflected heat and possibly shallower soil due to the wall footing.

No, I don't have a block wall. I have a green belt on the west side and an arroyo across the north side. I have other plants on the edge of the arroyo which are doing fine. I have plants on all sides of the house and they all do fine except for the NW corner. I am wondering if should try to mix some potting soil around them to improve the soil.

Possibly the soil is shallower in that area. Have you tried digging down until you hit caliche?

If the soil is the same depth as the rest of your yard, try mixing in a few bags of compost. You might also sprinkle in some mycorrhizae or other soil innoculants to liven things up.

PS, I wouldn't bother with the Miracid; you really only need that for acid-loving plants or if your plants are chlorotic.

Most of my plants were put in by the landscapers, but the sissoo and the bird of pardise were put in by a yardman that I hired. I have never seen the calishe. I will try composting with the mycorrhizae and see what happens. The soil is alkaline and I was told that a plant can't absorb the nitrogen in fertilizer unless the soil pH is close to 7.0.
Thank you!