How does lumb auto harvesting work?

Just wondering if lumb harvesting is like an AOE, or if they can just harvest the whole plant no matter what. I want to build some compact lumb ranches in a CO2 pit for Blum Lumbs, but in order to feed the 2 I want per ranch I’d for sure need the Ovagro nodes to grow up on the walls. Will I need dupes to go in and harvest the ones on the walls for them or will the lumbs still be able to take care of it?