They do reliably winter kill in my climate and pretty much rot away by early spring, leaving nice holes in the ground. The downside is the occasional rotten radish odor
John Elliott wrote:I planted some the first winter I moved onto my piece of the "bright red Georgia clay". I have anywhere between 4" and 10" of poor soil on top of heavy clay that goes down at least 100 feet (the kaolin mine down the road can vouch for the local geology). I was amazed to see that tillage radish would bore right in, because during the summer when it dries out, the clay takes on the hardness of concrete.
But planting tillage radish is only one tool to improve soil fertility. It may drill in, but it has insufficient biomass to increase the soil carbon much. For that, I also used truckloads of wood chips. Tillage radishes can lift up out of the ground so that their crown is 4-6" above grade. This allows you to put down a heavy layer of mulch and as the mostly-water radish rots, the mulch can fill in the hole and support more soil life.
I can't say that tillage radish improves the worm population of the soil. When I pull up a tillage radish, I never find an earthworm in the roots; they seem to prefer lurking among the roots of dandelions, chicories, and other tap roots that have a lot of side branching. Maybe the fact that radish is fairly smooth until you get quite a ways down makes it unappealing to worms.