" Hardening off" is the term used to accustom seedlings to life outside the sheltered environment of their humidity domes. When plants are in such a Humid environment they have no cuticle which is a covering that protects leaves from being dessicated in a drier environment. To harden them off you crack the lid a little more for longer periods each day until the plant grows a cuticle. The same would apply to your Vanilla roots. To go from 90plus % humidity to 60%is just too drastic. plus my experience with Vanillas is that they do best in humidity greater than 60% I would say 70 is best. but they can tolerate lower during the day if you can raise it during nighttime. My greenhouse drops to as low as 30% during the day but I get it consistently to 75% or better (preferably) at night. Hope this answers your question.