When I mention to someone that there's luffa in the garden I nearly always get a quizzical look and a response something like "doesn't it come from the ocean?"
“Nope, it doesn't come from the ocean . . . there it is growing right there!”
Luffa requires a long growing season (180+ days) so plant early. A good harvest of luffa means that you do not need to grow them every year, a single good harvest can easily yield two or three years of sponges. We grow ours next to our shed and allow it to grow up the side of the shed and over the roof—otherwise unused space.
Luffa is harvested after it turns brown on the vine and the vine is dying down. This can be hard to guess in our Southern California climate as many plants do not succumb to our coastal winter with lows not dipping below 50 degrees. But, if you want nice, voluptuous luffa be patient and wait for the squash to mature.
After harvest the luffa can be left in paper bags to dry more. Remove the outer flesh, bang out the seeds, and cut into desired lengths.
There may be some spots or discoloration on the luffa, simply use a white vinegar solution of a cup of vinegar to a quart of water. Soak the luffa for one hour in the vinegar solution and rinse well. You can also remove any remaining seeds with a chopstick while the luffa is still wet. Luffa can be further bleached by drying in the sun.
Grow luffa, grow your own sponges!