My pots aren't biodegradable, but they are reusable. Here's what I do, in case I haven't posted it here before. (I think I have...?)
Collect plastic containers like quart yogurt/sour cream containers. Save the tops too, and put some small holes in it, but not too close to the edge, so you don't weaken the plastic too much. Cut the bottom off and put the top back on. Turn it over so the top is the bottom.
Now you have a pot. Fill with your potting medium, plant seeds, water, give them sunlight, encouragement, music, happy thoughts.
When it comes time to transplant them into the garden, dig your hole, add any amendments you like. Take the bottom (top of the container) off, set the pot in the hole, and gently slide it up over the plant. The slope on the side of the container really helps with this.
Because the pots are decent sized, you can start your plants earlier and not need to up pot them. I've been doing this for several years. I ask friends to save me their containers, so I've gotten them for free. You do need a fair amount of potting soil, so it helps to make your own if you can.