turnip
菔 centers on the turnip plant, specifically its edible root. The meaning is straightforward and botanical.
菔 combines the grass radical 艹 with 服, which likely provides the sound. The character was created to name the turnip plant.
The grass radical 艹 sits above 服, like turnip leaves growing out of the ground. The lower part 服 can be thought of as the turnip root itself, clothed in soil.
For ホク, imagine a turnip being served as a side dish with a hock of ham: hock -> ホク, and the turnip is the star of the meal.