greens, vegetables
蔬 centers on edible leafy plants: greens and vegetables, especially those grown for food.
蔬 combines 艹 (grass/plant) with 疏, which likely contributes the sound and may relate to sparse or spread-out growth, but the exact historical development is uncertain.
The grass radical 艹 sits above 疏, which looks like a spread-out field. Picture a field of leafy greens growing sparsely but steadily: 蔬 means vegetables.
For ソ, imagine sewing (ソー) a patch of vegetable greens into a quilt: sew -> ソ, and the greens are stitched together.