For everything there is a season and a time for every purpose; a time to plant and a time to harvest. Convienient thimes are chosen to plant according to the increase and decrease of the moon and with aspects of the moon unto such planets as most aptly serve a particular plant. This must also be with harvesting.
The time to harvest depends entirely on what is required of the herb and the individual plants cycle. Spring is the time whe the plant is in its most full perfection, when in the bud, and when the heads are being formed for flowering but not yet fully opened. This is the time when the volotile oil content is highest.
If any member has a favourite herb, oil, or flower post here.