Many Taiwanese cultural events are based on the traditional lunar calendar. The three most important holidays are Chinese New Year, Dragon Boat Festival, and Moon Festival, and the dates for these are determined by the lunar calendar.
The Chinese lunar calendar has been used for close to 5000 years. It consists of 12 months of 29 or 30 days with the first of the month falling on the new moon and the full moon occurring on the 15th.
In order to keep step with the solar calendar the lunar calendar has a "leap month" every 3 years or so. These leap months are repetitions of a particular month, so there could be two "Augusts" or two "Septembers" in a leap year. Without these leap months the lunar calendar would be almost useless for agriculture since the planting and harvesting dates would gradually shift over time.
Besides leap months, the lunar calendar also has 24 solar markers determined by the position of the sun. These markers are called jie qi and are equal divisions of 15 degrees along the ecliptic.
Jie qi are very important for agriculture and dividing the year into seasons. They are integrated with the lunar calendar so that the Chinese new year is usually the new moon closest to the date when the sun is at 315 degrees - approximately February 4th on the Western calendar.
Each of the 24 jie qi has a descriptive name like "awakening of the insects" (approx. March 5th), "grain rains" (approx. April 20th), and "descent of frost" (approx. October 23rd).
Each of the four seasons begins at one of these jie qi. The seasons are centered on the solstices and equinoxes, so Spring starts around February 4th, Summer starts about May 6th, Fall starts about August 7th, and Winter starts about November 7th.
These seasons are applicable for "average" agricultural areas, but tea grown in the high mountains of Taiwan follow a slightly different seasonal appellation. Because of the cooler temperatures at high elevations, the beginning of spring occurs later as the altitude increases. Similarly, fall and winter start earlier at higher elevations.
High mountain tea (grown at elevations of 1000 meters or more) follows this harvest schedule:
Winter tea is considered to be the best tea of the year followed closely by spring tea. Except for Bai Hao tea, the oolong teas carried by Tea from Taiwan are exclusively spring and winter teas. Bai Hao is not a high-mountain tea and is only produced in the summer.