Greetings,
Are we talking bulb sensu stricto or anything tuberous. If true bulb, I
second the Crinum bulbispermum suggestion - though I don't know how dense
they are. Tim, did you weight the 20" dia Crinum you dug? I know Brunsvigia
josephinae can push 40 lbs.
If tubers are in the running, then I think a number of curcurbits are
the champs far and away: Marah species have documented tubers over 400 lbs
- and that was just the portion of the tuber that was extracted and
weighed. I have unearthed the top of one that was easily as big as a
recliner.
-|<ipp