thick, lush, in clusters
穠 centers on dense, abundant growth: plants that are thick, lush, or clustered together. The idea applies to any vegetation that is full and flourishing.
穠 combines 禾 (grain/plant) with 農, which likely contributes the sound and the idea of thick, lush growth related to farming.
Grain 禾 growing thick and lush like a farmer's 農 field: the plants are so dense they form clusters.
For ジョウ, imagine a lush field of grain so thick it looks like a soft green carpet you could lie down on: the word 'joe' (as in a comfortable, familiar name) sounds like ジョウ, and you picture yourself relaxing in that lush growth.