I have no idea what "zone" I live in and I'm sure most people would say that my area is cold, but here in Lillooet we have very hot summers with very little rain (usually) :) If you were to look on a map I live about four hours north of Vancouver BC Canada. Growing luffa in my area you will have to do things a bit differently than if you lived down south with heat year 'round. Here's my mistakes and what I will do differently next year.
Germination: I tried two different ways and found soaking them in a plate of water for two days, with no paper towels, and then planting them worked the best. After planting I placed them on a germination box set near a very hot woodstove. Four days later they spouted. (I have read that sprouting can take as long as 3 weeks!)
I started them way too early: March 3rd. My house is HOT, I had sprouts in four days, and full grown plants when it came time to take them outside. Next year I will time it so they are only in the house for roughly 3 weeks so a good time to start for me would be May 1st. If it's a bit chilly at the end of May at least they will be small enough to place covers over them. This year when I was able to plant them they were well over five feet long with numerous vines already growing, impossible to cover. I planted them at different times and first lost quite a few to transplant shock, then we had a freak snowstorm and I lost the second batch, and finally when I planted the last three I still had in the house, they lost all their leaves and I thought for sure they were dead. I kept watering them and eventually saw small green growing from the bottom, essentially they had started over from scratch.
I did have a few cool days when I threw an old wool blanket over them on the fence and I'm not sure if it helped, but they continued to grow. You might want to pick a spot where it's not too close to your house because the number of wasps and bees were crazy. Luffa seems to flower the whole season so the insects were constant.
Harvesting: I picked a few long before they were ready, thinking they were ready. I peeled them with a carrot peeler like I had seen at one site. This did NOT work. The flesh inside was still very fleshy and the seeds were impossible to get out without pretty much destroying the luffa. The seeds were white and very small. The fiber was not out to the edge of the peel and I lost a lot of the luffa. They more resembled a zucchini inside and I would not do it this way again. Lufa has to be dry, such as at this site, but in my area the luffa is still growing and hasn't got to that dry stage when our cold weather hits. I waited until the first frost killed the vines, after a few days I cut the luffa at the stems, leaving enough stem to tie a string on them. I hung them by our woodstove and let them dry completely. They became very light and the peel cracked when you squeezed them. I cut both ends off with a serrated knife and could see the flesh inside was now like cotton. I then tried to peel it, this was very difficult. I started running water over it and the peel came off much easier, the flesh washed out really well, and the seeds coming out were black and most of them washed out with the running water. I'm sure the black seeds will be good for planting next year, unlike the under developed white ones.
After getting all the seeds out I soaked the luffa in bleach water and here's my finished product:
I still have many hanging by my woodstove that haven't completely dried but this smaller one was pretty much ready.