Sometimes we have a shower curtain too long. We must not shorten it from the bottom, if not the leaded base will disappear or it will not be down anymore. It is necessary to make a clamp at the top just below the rings and to sew with the machine for example.
From above, it does not get wet or hardly and anyway would dry better.
On the other hand if we made a bottom hem, it would always be wet and would have more difficulty to dry, hence the risk of mold.
There are also shower rods that can be adapted to several widths. They are placed at the desired height and adapted to the length of the curtain.Suggest a tip for this theme