Hi transplant, I think you may be confusing mulch and compost. Mulch is a substance, organic or inorganic, that lies on top of the soil and whose main purposes are to regulate the soil temp, preserve moisture and help prevent weed growth. In your case, the rocks are your mulch. As far as feeding your plants, I'm just going to speak in broad generalizations here. Many xeriscape plants don't like rich soils or a lot of fertilizer; however a light feeding of most of them once a year is usually a good thing. Don't use a fertilizer high in nitrogen at this time of the year - nitrogen stimulates green growth. I use a liquid, organic formula that can be either sprayed on foliage or poured onto the soil. This works well for rock mulched beds. Again, this is just a generalization and you might want to do some research about the individual needs of your plants. Hope this helps.

I kinda like how the graining in the center panel flows like the granite (bottom pic). Yes... I love the stone as I"m a fan of "flowy" granites.

I'd just flush it thoroughly by pouring a volume of water = to the container volume through it 5-10 times. That should do the trick. I wouldn't plant in it w/o flushing it. Al

It will rebark itself for protection right? ==>>> are you asking if its genetically capable of surviving without your interference ... lol .. one would hope so ... e.g. bark of young maples is smooth ... maybe upwards of a decade ... but sooner or later.. and we always have to think in tree time ... the bark matures and changes ... it doesnt necessarily mean anything is wrong ... its not a great link.. but see the differences https://www.google.com/search?q=bark+of+young+maples&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjciu_bzP_NAhXix4MKHe4KBgYQ_AUICCgB&biw=968&bih=745&dpr=0.9 i am still wondering about being planted like a telephone pole.. and wonder how deep the root flare is ... another link ... https://www.google.com/search?q=bark+of+young+maples&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjciu_bzP_NAhXix4MKHe4KBgYQ_AUICCgB&biw=968&bih=745&dpr=0.9#tbm=isch&q=root+flare sooo ... my bottom line ... its not some hundred foot tree hanging over your house.. so no immediate need to do anything proactive.. unless you are interested enough to pull back some of that soil and grass around the trunk and find out about that ... but again .. in tree time.. it may or may not be an issue... within a decade or so ... ken