I collected eight plastic bottle at our Town recycling center. I cut them open then added potting soil and planted flower seeds. After taping the bottles, I dug out a spot for them in a south facing area of my yard and then buried the bottles. This method is good for all sorts of cold hardy seeds, especially flower seeds that often need a chilling period. The bottle makes a nice little greenhouse and the hole at the top is perfect for letting in just the right amount of moisture.
I’ve tried this a couple times before. Sprouting has always been really good the hardest part is getting the seedlings out of the bottles before they are fried or rot.