Grow your own luffa sponge! Luffas like full sun and a well-drained but moist soil, enriched with plenty of compost or well-rotted manure. They are grown like a winter squash or hard-shelled gourd and their long (30 feet isn’t unusual) vigorous vines need lots of room to roam or a sturdy trellis to clamber over. They require a long season to ripen, so start indoors early and protect from frosts later in the season.