plant
葍 refers to a specific plant, likely a type of bindweed or morning glory (ひるがお). Its meaning is narrow and botanical, with no clear abstract extensions.
葍 combines the grass radical 艹 with 畐, which likely provides the sound. The exact historical development is uncertain, but it is a phono-semantic compound for a plant name.
The grass radical 艹 sits above 畐, which looks like a full container. Imagine a plant that spreads like a full container of vines—bindweed covering a field.
For フク, picture the plant's vines wrapping around a fuku (服, clothes) left on the ground: fuku -> フク, and the bindweed covers the garment.