Using 4x4 with Mel’s mix in one box and my own mixture in the other. I am going to rip up the one with my own mix, add some phosphorous and some other goodies and replant.
See what happens.
My raised beds are 12” deep, and I use pure horse manure. The only other fertilizer I use is the rock phosphate. If your soil is anything like mine (caliche) you’ll have a high soil pH and will need amendments. If you have a deep soil base, you may just try adding the amendments to the soil, and checking it for pH. Many plants seem to like it when the pH is 6.5-7.0.
The big issue is keeping it there. You shouldn’t be going wrong with compost. Make sure you add a lot of mulch to keep the rootball moist and cool.