The .months field isn't required, the game defaults to all months if that is ommitted. I haven't checked bonus or malus values, but I'm confident they will default to something as well (probably an empty table, i.e. no bonus / malus months).
The reason Dogbane is so hard to find is that it was recently (42.4?) moved from Firewood (which is very common) to WildPlants (which is not).