You might be interested in this post https://growinginthegarden.com/sunken-garden-beds-water-wise-gardening-in-the-desert/ there is more information about this type of gardening. It should work well for you. I would recommend compost from Arizona Worm Farm.

Now, instead of a traditional raised bed, I have what I’m calling a “depressed garden” (but I promise, it’s still full of hope!) 🙂

My next step is choosing the right soil mix to fill this space and provide the best conditions for growing vegetables in the Phoenix area. What type of grow mix should I use, and where’s the best place to buy it/have it delivered? Any recommendations from experienced gardeners would be greatly appreciated!

Hi Rose. I checked with Zach at Arizona Worm Farm about your question, and here is his response: It’s almost certainly a saprophytic fungi. Probably nothing to worry about – it supports nutrient cycling. I generally recommend just adding compost regularly and growing stuff. If it get so bad that stuff won’t grow, the whole bed needs to have the soil replaced. Now (and if they have to replace soil), skip the mushroom compost – it adds a ton of fungi.

Ashes are very alkaline – only add them if you have acidic soil, as it would raise the pH. Don’t use more them for than 5% total of your compost. I would only use ashes from untreated wood as well.

Sure.

They’ve had a hard time keeping up with demand, so selling it in other locations hasn’t been feasible. They do offer pick-up but yes it is a drive from the Eastside of the valley for sure.

@Angela Judd,
Hi Angela, In addition to adding wood chips, twigs, etc. to fill up half the height of the bed, could one mix in straw?

That sounds great. Thanks for the recipe.

Hi. I wouldn’t use sand or rocks, but you could absolutely use wood chips, branches, twigs, etc. to fill up to half of the height of the bed.