firewood
蕘 centers on firewood and the act of gathering it, with the woodcutter sense being a natural extension of that activity.
蕘 combines the grass radical 艹 with 堯, which likely contributes the sound. The exact historical development is uncertain, but the character is associated with firewood and gathering brushwood.
The top grass radical 艹 suggests plant material, and the bottom 堯 looks like a pile of sticks being gathered. Picture a woodcutter collecting fallen branches and grass for firewood.
For ジョウ, imagine a woodcutter named Joe gathering firewood: Joe -> ジョウ, and Joe the woodcutter piles up the brushwood.