In my search for biodegradable planting pots I came across these ingenius newspaperplanting pots. Like these instructables:
https://www.instructables.com/id/Make-biodegradable-seeding-pots/
https://www.instructables.com/id/How-to-make-organic-planting-pots-using-old-newspa/

I really liked the concept: using old newspapers to make pots for growing seedlings.
I did not like the lack of stiffness.

That is why I added one more ingredient to the newspaper planting pot.....WATER....

...Oh, your hands might turn black by the ink. If you worry: remember this your hands will get dirty anyway, it`s the soil bb :)

Step 1: Materials Needed.

o Newspapers (torn in 6x60cm)
o A little plastic seeding pot (mine is 5cm in height, 5cm at the top and 3.5cm at the bottom)
o Water

The platic pot is handy as a 3D template. U might want to use another template. Take notion: the flexibility of the pot comes handy in step 5: Taking out the template.

Step 2: Wrap the Template

Wrap one piece of paper around the plastic pot. The paper should be wider than the pot, so u can fold it around the bottom. The best is wrapping it as tight as possible. But don`t despair if it is slightly loose. The water in the next step will stick it all together.

Step 3: Water the Pot.

Put the paper under a running tap and soak it. OR SOAK IT IN A BUCKET OF WATER (you will not spill that many water). Then sqeeze all the excess of air and water out of it Making a kind of papier machee without the starch.

Step 4: Repeat Step 2 and 3

For extra strength, I wrap around another piece of paper, soak it and squeeze it.

Step 5: Taking Out the Template

Be carefull when you pull the template out of our newborn newspaper planting pot. This time the flexibility of the template comes handy, because the wet newspaper is very fragile. When the template is stiff it might be harder to remove and u will end up with an nice papier mâché ball.....

Step 6: Set It to Dry Overnight

The paper is still very wet. I set it to dry overnight and plant my seeds the day after. Ok that might be a long time for the impatient gardener. But hey, u can make a bulk of these and store them for whenever u need them.