Cephalanthus occidentalis

So I planted 50 button bee seeds in segmented planters, ~1/4th- 1/2 inch deep, equally spread out. I watered appropriately, i have a bright grow light, and its been over three weeks since I planted them. Only two have sprouted, in succession. The two that have sprouted are very healthy. I dug the unsprouted seeds up and they were either spongy, breaking apart, or just dormant. This exact set up (besides for planting depth) worked extremely well for two other seeds, swamp rose mallow and bee balm. And button bush is supposed to be easy to germinate! The main problem was that most of the seeds very easily broke in half. So I do think there was something wrong with the seeds and it wasn’t due to improper germination conditions.