Plant pots from egg boxes, yogurt cartons, newspaper...

[honeybee13]

If you grow your own herbs, fruit and veg and so on, you don't need to buy plastic plant pots. Here's a list of seven common household items that you can use as seed pots.

 

I've used cardboard egg cartons - the advantage is that if the roots grow through the side of the little pots, you can just cut up the egg box and put each seedling straight into the next pot without disturbing the roots.

 

https://www.treehugger.com/lawn-garden/diy-seed-pots-common-household-items-starting-seeds-indoors.html