Plants absolutely hate my 3 yr old Sunken Hugelkultur in the desert. I want to fix it.

Hello,

This sunken Hugelkultur is 3 1/2 years old and it’s absolutely one of the worst performing beds in the food savannah this year. Giant sunflowers did okay, as well as garlic and onions, but nothing else.

1. It sinks
2. It floods 2-3x a year. It does drain, though.
3. I mostly plant desert adapted crops (flour corn, melons, amaranth, millet, onions, garlic), so maybe an underground swamp is not the right fit for for me.
4. It seems to both get too wet and too dry / drain out too much. The native soil beneath it is “excessively drained” loamy sand.

5. My ecosystem lacks worms. The sand is too sharp here, and they are not endemic. I feel like worms might be key to success with this. There are lots of insects in the first 2 inches of soil, but not below that. The ants that till my soil in other places won’t go here. I don’t want to add worms.

   I have deposits of amazing volcanic river sand here, and I was think of filling it to the top with sand and some composted manure. I could plant my garlic there over the winter. I figure the roots at the top would get more oxygen and more consistent moisture, and could also reach for the loam beneath or not.

Or I just plant the whole thing with native switchgrass and forget about it.

Any thoughts?