When you first see them, soil blocks are both unremarkable and fantastic. They’re just cubes of dirt, after all—big deal—but they function like a pot of earth twice their size or more. In fact, the headline could read: Pots Obsolete—Soil Blocks Replace Plastic. Implausible? Perhaps. Impossible? No.

Unlikely as it sounds, a cube of free-standing soil can sprout a seed, support a seedling, even grow a full head of lettuce.

How is this possible? And why don’t the darn things just fall apart, without any container to hold them together?

Jason Beam, of Potting Blocks, sells soil blockers, the presses used to make soil blocks. He joins me this week to answer these questions and many more. Here’s a sample of some of the topics that arise in the course of the conversation: Why is transplanting a seedling several times a good thing? Which holds heat more effectively, air or water? Is peat moss a renewable resource? Just how many grades of coconut coir are there?

I won’t claim that we answer all these questions definitively, but it’s a lot of fun. And the central questions about soil blocks—what they are, how to use them, and why they’ll give you increased germination rates and sturdier seedlings—these do get answered.

Check The Manic Gardener for further background and links.