Hi figs....do not listen to your neighbor. Container mixes are "soil-less" because of drainage, primarily. Folks who include native soil in their containers are usually trying to save money...a bad idea. Now, as far as your plans on the mound...I really like your idea on ingredients. In that case...you want to incorporate some native soil so your plant can "transition" from the mound to the native soil. It is just a better way to "blend" the mound/native soil. Stick to your guns and do it your way...it will be fine. I would go at least 50% native soil...maybe more. Also, till the ground well before putting your mound on top...and mix in some gypsum along with your mix. PS Put about 3-4" of mulch on top of the mound. Wooden chips from landscapers (free) are used effectively around here. Hope this helps...

Thank you so much Fireduck, sorry, I made an almost duplicate post in one of my other posts asking you the same question. My only problem will be incorporating so much native soil. Since there is no digging required for a raised bed, I don't know where I'll get that much native soil from. I suppose I can dig a hole from somewhere else in my yard, take that native soil and put it in the raised bed, then fill that hole that I made with some bagged dirt.

Here's some pics. I thank that the size (5 x 4) should (hopefully!) be enough room to get those horizontal roots growing. I was thinking of putting down a weed blocker sheet down (to try and keep the grass from growing into the avocado roots), but then I wonder if I should leave it out so that there is no interruption of soil "flow."

Fireduck, thank you SO much for your advice!