mugwort
蒿 centers on the plant mugwort, a specific aromatic herb. The meaning is narrow and botanical, without broader abstract extensions.
蒿 combines the plant radical 艹 with 高, which likely contributes the sound. The character originally referred to mugwort or similar weedy plants.
The top 艹 is the plant radical, and the bottom 高 suggests tallness. Picture a tall, weedy plant growing high in a field: that tall plant is mugwort.
For コウ, imagine a tall mugwort plant growing so high it reaches a coat hook on the wall: coat hook -> コウ, and the tall plant hangs from it.
black-faced bunting (Emberiza spodocephala)