Are they getting at least 6 hours of direct sun a day? Leafy vegetables are fine with less (in fact usually you get bigger leaves with less sun), but plants like tomatoes and squash need lots of sun.

When you filled up the amendments into the raised bed did you compact them down? Those amendments you listed can make a very aerated soil with the wrong ratios. While aerated soil is good, it's only good to an extent. If you have pockets of air in the soil, you'll have problems with roots drying out. This is one reason I always add peat moss to my "gritty" mixes.

Another thing regarding soil composition, it relates to how much water the plants should be getting. If you have very aerated and fast draining soil and it's getting at least 6 hours of sun a day, you probably need to water those puppies at least once a day in the growing season here in AZ. You can tell if they need water by sticking a finger into the soil about 2 inches down when you think it's time to water. If it feels wet/soggy, it's probably over-watered and that can cause some plants to die. If it's bone dry 2 inches down, you need to increase the frequency of your watering schedule.

They are. My wife thought that I was nuts when I told here where I wanted to put the beds (pretty much the middle of the yard), but they get sun from sun up until about 4:30pm. The winter garden loved it. I've got the ability to put shades up, but I'm holding off on that until it starts to get hot.

The compaction idea is interesting. That's part of the reason I've been so up tight about monitoring my watering. It does drain pretty fast, but below about three inches is seems to stay moist for a couple of days right now. Above that, it does dry out pretty fast. Not sure how that will hold when the heat rolls in. The part of that throwing me off is that the soil seems to have a nice structure to it. If I ball up a bit of moist soil in my fist, it holds it's shape. If you poke at it, it falls apart, but it has structure.

Thanks for the advice.

It does sound like it's drying out too fast. When it comes to potted plants or raised garden beds, I like to err on the side of slightly too much water, especially once the temperatures start going over 90.

It's pretty hard to over-water potted or raised bed plants in the heat when they have fast draining soil. Some of my smaller containers with full root systems get water 2 times a day once May rolls around and they are still weightless by the end of the day, and they are kept in mostly shade. That's how I know when my smaller pots are watered properly, by their weight - easy to tell if they have too much or too little.

I've found the most important thing is consistency with watering. I used to water by hand and I lost track of how many blueberry plants died on me. Once I switched to automatic watering I've only lost 1, and that was because the emitter fell out of the pot and I didn't notice. It was only not watered for about 1 1/2 days.