I found the commercial tree pots too hard to remove seedlings from without ending up with a bare root to plant. I found a better system.
I took their idea of those little ridges that encourage roots downward but made a pot that's easily removable and reusable.
Using corrugated plastic sheet(like cardboard) I carefully split the layers so you end up with a sheet with little ridges. Wrap this into a tube that fits inside a 3" PVC drain pipe. Then I wrap with some clear packing tape. You need the pipe at first to pack the potting soil fairly tight (at least the bottom third). Once the soil is packed you can remove the packed soil tube and stack (16 of them fit inside a milk tote lined with weed barrier cloth).
The ones I made this year for tree seeds are about 10" high. Great for most tree seeds but are too short for oak and walnut, the taproots are just too long. Next year's will be 16" tall for nut trees.
I'm also big fan of PRO-MIX BX MYCORRHIZAE potting soil.
http://www.pthorticulture.com/en/products/pro-mix-bx-mycorrhizae/ When you go to plant just cut the packing tape and you have a perfect tube to set in your planting hole.
This past January I put apple and honey locust seed in potting soil in the fridge for a few months. In March or so I put them out in warmer air. After a few weeks I carefully put the sprouted seeds in these pots.
This pic were takes in early August as I was planting them. It's a bit blurry but you can see how nicely the roots have extended right down and out the bottom and how healthy the trees look after only 5 months.
This is one of the apples I started from seed.
My pie came with a little toothpic holding up this tiny ad:
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