Are you feeding the plants? Supplying nutrients in any form? Working in a great deal of compost if nothing else?

You are essentially growing in a container, although a large one so any of the soil-less container mixes (recipes on the Container gardening forum here) would work well. But even then you need to provide a regular supply of the essential nutrients and micro-nutrients for good growth and production.

While manure may provide some low level nitrogen there is little else in your mix listed so far. There are an almost unlimited supply of nutrient additives - both organic and synthetic - that can be mixed in but to know what your soil really needs most you need to have a soil test done. Local county ag extension office - $10-15.

Dave

Loam and manure sound good, providing the manure is well composted, but adding sand to clay is a recipe for cement. I'm getting good results with the Square Foot Garden mix - peat, vermiculite and compost in equal parts, but when I first started my raised bed, I just added Amend to the native soil. Mine was clay, too, but probably not as hard as Phoenix clay. One positive aspect of clay is that it contains lots of minerals.

Here is a link that might be useful: My raised bed garden

I don't know about adding sand to Arizona clay, but I've been adding sand to New Jersey, Oregon and Washington clay for about 40 years now, and it works great. You have to add quite a bit of sand for it to really work. Like 1/4 to 1/3 by volume. Google "soil triangle".

The real problem here is that ddot15 is giving us almost no information. Have you had a soil test done? Do your neighbors grow good vegetables? Is your soil still extremely dense, even with the sand? Do weeds grow in your soil mix?

You are growing in an 18 inch deep container, right? Soil with some sand mixed in is not going to drain well in that situation. That's why they make potting mix. It's very coarse, so it drains even in a container. Your plant roots need oxygen. They can't get it if they are in saturated soil. You can break up your soil mix by adding perlite or pumice or gravel to it. Sand isn't good enough; its particle size is too small for container mix.

Are the sides of your containers shaded from the sun? If the soil gets too hot, the roots will die.