Sh'mal was so happy when his daikon radish went to seed. He told me he'd collected the seed from season to season. He's replanted these radishes for years. Same with the collard greens. That's what sustainable means.
So, it's best to plant the seeds just as deep as their thickest side. Plant near the new moon phase. Keep the soil moist. These tips come from John Jeavon's "Grow More Vegetables" book. I heard somewhere that it was best to plant the eve of a full moon. John's book gives a very good explanation why it's best to plant during the new moon phase.