http://www.gamesas.com/topic/1404470-resetrespawnregrow-floratreesplants-in-a-noresetzone/page__p__21435777__hl__skse%20respawn%20plants__fromsearch__1#entry21435777
Check out the SKSE function (down at the bottom of the topic).
Will that help?
(note that I am not certain the realse version of SKSE has been updated to include that new function!)