I’ve grown luffa with ok success in coastal northern Spain (zone 9/10) but the fruit don’t always ripen (leave alone dry) on the vine before winter humidity kills the plants. Instead of drying the whole fruit (with a high risk of rotting) I clean the pulp of the fibre straight after harvest and just dry the fibre skeleton. It works well even for immature fruit - at least well enough to use them as kitchen sponges.
