Air prune beds

I want to produce a lot of tree and shrub saplings, but only have a little space to work with and haven't moved to my final property yet. I've seen videos about air pruning beds, and they look ideal for what I want to do. Has anyone here used them? Is there any major downsides/reasons why everyone doesn't do it?

I've built four 1'x2' air-prune boxes that sit ~1.75" off the ground. Right now I have them on a short stack (3, maybe) of pallets, but last year they were on grass and many, many weeds grew up through that 1.75" and into the boxes. It was a proof-of-concept thing, based on Sean's work at Edible Acres, and I think now that I'd rather develop beds of deep, highly friable soil and grow in in-ground nursery beds. I've also found that trees love being planted in Mel's Mix (from the Square Foot Gardening technique) and they're very easy to get out of that for transplanting, assuming you have it deep enough, so I'm doing that while I work on building those cushy in-ground beds.

I've been growing seedlings in 1' x 2' air prune boxes for about 5 years. I love it. I keep adding more.

Mine are on a balcony so that I don't have to cage them off from squirrels. I therefore don't get the surprising weed problems that Christopher mentioned.

APBs are great and I’ve been using them for nearly 5 years. One thing I’ve found is that not all trees respond well to growing in them. Northern red oak in particular seem to have stunted growth when starting them in APBs. I have a large batch of them that are only 4-5” tall after 2+ years.

Another thing I’ve realized is that only certain trees need to be grown and in them. Mostly trees with taproots. Everything else I start in raised beds/mounds and they seem to do quite well when transplanted.

I’ve come up with a few different ways to build them, but like previous comments, if they’ll be situated over grass or soil you should give them at least 10” between the bottom of the bed and the ground. Moles and other critters can find them to be great places to hide under and then pile up soil that the trees will grow into.

Hope that helps. Good luck!