I had a feeling something was wrong, so I started brushing the soil away with my hand and didn't see any roots; pulled up one of my triple crown blackberries and there were no roots! And little white worms munching on whatever was left of the roots.
I'm thinking about transplanting the other two, but I just doused the area with Epsom salt for now. Not sure if it'll do much, just kinda figured the sulfur in it might drive those little critters away.
The other two plants do seem fine, but I'm worried. I won't be using miracle gro again.