I have minature Rosette Water Hyacinths I could send for postage

I'm in Sedona and have planted lots of natives. However, Northern Arizona has a wide spread in the microclimates from the lower areas like Verde Valley, Camp Verde 4000 feet to over 7000 foot elevation in Flagstaff. The problem is just because a species is considered a native, doesn't mean it is available at a nursery. Nurseries only grow what people will buy. There are more landscapes here that plant local natives compared to down in the Valley where I used to live. In the valley, people could risk plants that were hardy to around 30 degrees whereas here in northern AZ, everything must have at least hardy in Zone 7.

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.

Hi and welcome to the forum :) I'm making an assumption here but it looks like you used pure bagged mix for those plants? I don't know if that's the case, but it's most likely the root cause of the plants dying. (no pun intended) The pure mix will drain very fast and become hydrophobic (meaning it won't hold water anymore) in our summers. That white stuff is fungus that has grown from the excessive watering that that type of soil would need to keep even a little moisture in it. Plus the surrounding soil would become very bog-like and contribute to the fungus. Some types of fungus in the soil aren't bad for plants, but with that much fungus the conditions were probably ideal for lots of bacteria to thrive too. You want to mix that bagged stuff with native soil when you plant something, even in raised beds (not containers though, but that's a different topic). The *most* I will add to soil is about 50% compost (depending on how fine it is), and that's for something that needs very fast draining soil (not fruit trees), and the soil will be shaded by something, and the ground will have lots of mulch applied to it. Usually annuals like Pumpkins or root vegetables will grow well in this type of mix. Otherwise I use around 10-25% compost or none at all. You may still be able to save the trees. I would wash all the roots off, remake the soil for the planting area with lots of native soil and very little compost added. You don't need to do this, but if I had extra time I would bake that mix (put it under a clear plastic sheet out in the sun for a few weeks) before I used it again, otherwise I'd just buy new mix.