contrary to the first answer, i know that dried lavendar can keep it's scent for ages and ages. it is only when it is fresh (not dried) that that air scent lasts such a short time.
a couple of years ago, i made sachets out of dried lavendar i took from my garden.
to this day, when i crush the little cloth sachet in my hand, a very strong and clear scent of the lavendar inside is emitted.
without any friction, it will last a super short time. if used as a sachet or if it is rubbed in any way, the oils inside the dried lavendar will last for months... and, in my experience, even more than a year.
the sachets i made are kept in my dresser drawers. everything in those drawers continue to smell very clearly of lavendar.
so... i suppose the staying power of the scent is dependent on the way in which the dried herb is used.
i read that lavendar was found in the tombs of the pharoahs of ancient egypt and it STILL had maintained it's scent. now that's a LONG time!
also... here is a site that give all kinds of info about lavendar, including reference to the "shelf life" of lavendar's scent (5 years, they claim -see last few lines of the entire article) :
http://www.incensewarehouse.com/Spotligh…
hope this helps.
ps: did you know that you can throw these sachets in the clothes dryer instead of a dryer sheet... to help make your clothes smell fabulous when they're dry?
and did you know that dried lavendar acts as a moth repellant in your closet? interesting eh?
my own experience.