Harvest the mature gourds when they begin to turn brown, feel light and dry, and rattle when shaken. After the first killing freeze, remove any more dried gourds. Allow the remaining gourds to dry on the vine or bring them inside to a warm, dry, ventilated area.
The outer skin is easy to remove from mature, dry gourds. Soak the gourds in warm water until the sponge slips out. Slip your fingers between the outer shell and the fibrous material to release the sponge. To whiten the sponges you can dip them into a 10 percent chlorine bleach solution (1 part bleach to 9 parts water) after you've rinsed off the excess pulp. Be sure to follow the label's instructions when handling bleach.
Allow the sponges to dry thoroughly on racks or suspend them in mesh bags. The fruits from the luffa sponge gourd plant can be used as bath sponges or scrubbers for pots and pans. The tough fibers are biodegradable and can be discarded in your compost pile when you're finished using them.
