Luffa (or loofah) gourds are grown in tropical and subtropical climates. After the plant blooms, the flower develops into a long, gourdlike plant that resembles a giant cucumber or zucchini.Once they're completely dry, they can be sliced and be used as sponges – either you use them for showering, doing the dishes or both! Being entirely plant-based, luffas are perfectly fine to compost when they start wearing out.