Specifically in the case of cammas bulbs, the harvesting method was quite precise in its imprecision. The tool for gathering bulbs was basically a polished stick, which means that digging up a cluster of bulbs misses all of the offsets and a few of the larger bulbs. But the act of levering them out pushes the remaining bulbs outward from the center of mass, giving them more room to divide.

They also apparently gathered at flowering time, something you don't usually see in conventional agriculture. TtW suggests that this is because of Death Cammas - a hepatotoxic doppelganger with a completely different flower, that would be in the public interests to irradicate from your fields.

Cammas experts claim only an idiot would confuse the two, but harvest is a group activity. Some of those 'idiots' would be your kids or elders with failing eyesight.

I knew a guy who is trying to re-establish cammas from remnant native meadows who thinks the real reason is metabolic. That the fraction of inulin (one of the starches that make you fart) during flowering is lower, and hence they require less intensive food prep. Lewis and Clark apparently sampled underprepared cammas during their journey and spent a very unpleasant night because of it.