I purchased CowPots to start seeds — a giant box of 330 tall #4 pots was 60$ in 2017, and I have enough for next year still. Four years of seed starting comes to around 15$ a year (it looks like the giant box is now 80$, so more like 20$ a year). I love the things because they’re made of compost – no peat, no paper. And they claim that roots grow through th pot walls and the entire thing breaks down incredibly quickly once in soil.
I can attest that roots grow easily through the pots — I’ve started seeds and seen the roots break through (yeah, I should have gotten those things out to the garden sooner!). But I’ve always been curious how quickly the pots decompose in soil. Hard to tell, since it’s in soil. I’ve had some pots sit outside for over a year, so I suspected the “quick” decomposition wasn’t so speedy. The pots that had been sitting outside in the weather for over a year? I turned them into my compost pile. They’ve been there for about a week now. Which substantiates my suspicion that they don’t fully decompose in a few short weeks. Doesn’t really matter, since the plant roots are readily growing right through the pots … but we’ll see how long these things remain visible in the middle of a hot compost pile.