I finally tried out making a planter from scrap cloth. This tiny jade plant isn't yet at the point where it really needs water, but I'm hoping that the cotton will prevent overwatering without losing water so quickly that the soil stays dry.
The walls of the pot are made from 4 layers of cotton bedsheet material and I got to use the decorative stitches on my new machine to add a bit of stiffness. All biodegradable.