I don't know about the soft pots, but the tub would certainly work -- be sure to add drainage holes if they don't have them. This is the set up I use -- but in regular large pots, about 1/3 set into the ground, for winter I mound up straw or leaves around the sides.

If your planned bed is outside the drip line of the walnut, perhaps the soft pot would be enough protection. I have many things planted in ground about 10 feet away from one without problem.

I've used fabric pots (thick and thin ones) for different veg and a small fruit tree, they really dry out and require a lot of dedication to watering. I heard if you use a kiddie pool under with strategically placed holes you can improve it.

But I switched a few of my blueberries when they outgrew regular pots to blue barrels cut in half. They run from $15-25 each on eBay or Craigslist, so much cheaper than wine barrels. My spreading Burgundy variety berries had become a bit constricted so I was especially trying to find a solution without it getting out of control. They are on cement patio, overwintered fine with no attention or care after dormant and have now bloomed and are covered in more blueberries than before. (photo of barrel prepped before planting)

Thanks for you input. For the fabric pots I was planning to dig them into the ground...maybe just leaving the top 6" above ground...so that would help with drying out. I'm more concerned with the toxins from the walnuts seeping through the fabric. I guess I will stick with a more solid pot to be on the safe side and maybe not dig it in quite as deep.

I like fabric pots but from what I understand they do not last as long when they are in contact with soil, best used on concrete or asphalt. They say they last 3 to 5 years, it would be less if you put them in the ground. A fabric pot would do nothing to protect the toxins since they are porous. If using fabric pots you would need to leave them on top of the ground and move them inside an unheated building such as a garage or storage shed in the winter.

If you use the solid pots make sure you have many big holes drilled in the bottom for drainage. They will have a tendency to clog and you have no way of unclogging the bottom once they are in the ground. I would actually cut at least half the bottom out to make sure it had better drainage.

One more question. My daughter is making me cedar planters for my blueberries (so glad I enrolled her is scouting!). Would a 20x20x16.5 planter be enough room the following varieties: Blue Crop, Chippewa, Pink Popcorn? And would 15 x 15 x 13.5 be enough room for Glaze Blueberry, Jellybean, and Peach Sorbet? The plan is to dig these about 1/2 - 2/3 into the surrounding bed to provide some more insulation for winter.

We're also planning to build a structure around the berries to protect them from birds, so once we build the planters and plant them, we have no intention of moving them...ever.

I doubt even regular pots would work. In a couple years the blueberry roots will leave the pots through the drain holes and walnut roots will come in the holes. Either way the blueberry plants will grow great for a few years then get exposed to the chemical and die.

Best bet is just above ground pots and every month or so pick the pots up to sever the roots growing through them.