Leave it till 37 weeks and btw you don't ahem take the evening primrose capsules. AFAIK you stick them up your fanjo to ripen your cervix. Apparently . Personally I'd just wait for nature to take it's course, but do go for it with the rasp leaf. Also arnica, I didn't start till I had the baby, I hadn't thought of trying beforehand.
A friend and I both started taking raspberry leaf capsules at 35 weeks pg. Unfortunately I had an emCS at 36 wks so don't know if they'd have helped me but my friend went into labour just before her due date and although her labour was long her contractions were very efficient and baby was born fairly effortlessly (1st child).
RE arnica- it's advised if in labour to start taking it straight away, I was taking Arnica 30 3 times a day 24hrs before my CS and went on to take it 3x day for a week afterwards. Definitely aids healing- used it after both my DCs were born, and used arnica cream around my c-section scar (not on it) to aid bruise healing.
No idea re evening primrose!! But have heard lots of positive stuff re perineal massage from 35+ weeks, using sweet almond oil...
I'm sure others on here know a lot more than me! Good luck BTW