Some women can grow 8 feet of hair, some only 1 foot of hair. Typical is 4 to 6 inches growth per year.
There are many theories of nutrition and scalp massage and inversion to help hair grow, but no validated studies that give proof to the level that medicines for disease are tested to.
Very important to PROTECT the hair to avoid breakage of existing hair and loss of volume. Heat, sun, and abrasion are all detrimental. The very best hair girls wear their hair UP probably 90% or more of their waking hours.
Anecdotal evidence that semen is a valuable treatment for hair...but a difficult subject for many women who aren't into kink/fetish. Of course we'd all love a partner like Leona who worships cumditioning and used it to grow past floor length in perfect shape.
Good luck with developing a splooge partner...hard to imagine anything more satisfying than using your loads to promote your fetish.