Chinese medicine has long history of herb gathering, which even becomes an culture. People in ancient time that compile herbs have a well knowledge of the properties of the herbs and their actions, and they do so mostly for self-supply as most of them are Chinese medicine practitioners. It is said that a doctor, without knowing the herbs well, could not be a good doctor.
As it is written in “Xia Xiao Zheng”(《夏小正》),(which is composed 3600 years ago and was considered as the ancientest science writings in records so far) has this, “This is what is called herb gathering, the herbs are used for dispersing the pathological Qi”.

Through out Chinese history, there are all kinds of writings about herb gatherers, there is a poem tells a story that the poet visited a hermit without success as the hermit was going gathering herbs deep in cloudy mountains. Here is the poem.
Seeking Out Hermit In Vain
Jia Dao( a famous poet)
Beneath the pines I asked a boy,
He said master"s out gathering herbs.
Where is he? I insisted,
Somewhere in the cloudy mountains ,Deep in the fogs,
Barely could say where. 

Herb gathering in ancient time have very strict standards as to the time of gathering, the places herbs grow and the growth year of the herbs because these factors are related to the actions and qualities of the herbs. For example, Yinchen(Capillary Artemisia), which is a typical herb for jaundice, is said in a proverb that it only have medicinal actions when plucked in march( Chinese lunar year). if plucked in May or June, it is as the same as firewood(does not have actions at all).
But nowadays, for profits,people follow these ancient tips no more! What a pity!
But luckily, in the mountainous areas, this herbal tradition is still kept today, like in Guizhou province,China!