black clods of earth, shop, hut
壚 centers on a place made of dark, cloddy earth: a simple hut or shop built from such soil. The meanings are loosely connected through the earthy material and the humble structures it forms.
壚 combines 土 (earth) with 盧, which likely contributes the sound. The exact historical development is uncertain, but the character is associated with dark soil and simple earthen structures.
The left side is 土 (earth), and the right side 盧 looks like a complex shelter. Imagine dark clods of earth piled up to form the walls of a small shop or hut.
For ロ, picture a low hut made of dark earth: low -> ロ, and the humble shop sits low on the ground.