I buried a 16" diameter, 4' long log of bodock (that's what I grew up calling it...so that's what I call it) five years ago in a part of my pond that dries out every year, but the soil stays wet. I dug it up this past summer and cut a chunk off it....it was almost there....it was green about halfway through.
These were cut into six foot logs and buried a few days later.
In about 20 years I'll have some green.