Our Lilac bush has these strange green seed pods where the flowers have died off. I guess they're seed pods. They look like succulent leaves. I wanted to know when to harvest and how to preserve them.
Wait until they are dry and brown. When they are ready, the tip of the pod will start to split down the middle. On each side of the split there will be two chambers with a papery seed inside.
After they are dried, you can put the dry (and open) pods in a sack or container and give them a shake. Some seeds will fall out and some will be very stubborn and not want to come out of the chamber. I use a toothpick to ease the stubborn ones out.
After you have all the seeds you want removed from the pods, leave in an open container for a week or so to ensure they are dry. Package and keep in a dry cool place.