Major Heat (Dashu, 大暑) falls around 22-24 July at solar longitude 120°, the hottest time of the year, usually in the middle stretch of the dog days.
Solar longitude
120°
Type
Principal term (zhongqi)
Season
Summer
Order
No. 12 of 24
Usual dates
Jul 22–23
Meaning and Astronomy
Dashu (大暑) begins when the sun reaches ecliptic longitude 120°, usually between 22 and 24 July. It is the twelfth solar term, a zhongqi (中氣) or principal term in the sixth lunar month, and the last term of summer before the Start of Autumn.
Where Minor Heat signals rising heat, Major Heat marks its peak. Although the sun has been moving south since the summer solstice, land and sea continue to store heat, so for most places the period around Dashu is the hottest of the year, typically falling in the middle stretch of the dog days (中伏).
The Three Pentads
First pentad: Rotting grass turns into fireflies (腐草為螢) - ancient observers saw fireflies rising from decaying grass and thought they were born from it; in fact fireflies lay eggs in damp grass and soil.
Second pentad: The soil is damp and the air steamy (土潤溽暑).
Third pentad: Heavy rains come at times (大雨時行) - thunderstorms bring brief relief from the heat.
Climate and Farming
The middle and lower Yangtze is often under the subtropical high, with prolonged heat and little rain, sometimes reaching around 40°C. Northern China is in its rainy season, sultry and stormy, and southern China is hot and often affected by typhoons. Taiwan and Hong Kong are hot and humid, with typhoons and afternoon thunderstorms. As the saying goes, 'Minor Heat is not really hot; Major Heat is the dog days' (小暑不算熱，大暑三伏天).
In southern double-cropping areas the 'double rush' is finishing, as late rice must be transplanted before the Start of Autumn, and everywhere farmers guard against drought or flooding. The heat, though hard on people, suits warmth-loving crops such as rice and maize, and plentiful sun and rain lay the foundation for the autumn harvest.
Customs
In Zhejiang, people once set out free 'dog-day tea' (伏茶) in roadside pavilions, brewed from herbs such as honeysuckle, self-heal and liquorice. A Cantonese saying holds that eating grass jelly at Major Heat keeps you youthful, and grass jelly (仙草) is a favourite cooling dessert in both Guangdong and Taiwan. Taiwanese also eat pineapple now, in season and called ong-lai in Taiwanese Hokkien, which sounds like 'prosperity arrives'.
In Putian, Fujian, friends exchange lychees and eat warm-poached mutton to 'pass Major Heat'. In Jiaojiang, Taizhou, Zhejiang, communities 'send off the Major Heat boat' (送大暑船), floating a model boat out to sea to carry away plague and misfortune - an important local folk ritual. Hong Kong and Macau have few customs specific to Dashu, though staying cool and preparing for typhoons dominate daily life.
Seasonal Food and Wellness
This is the time to take heat most seriously: avoid strong sun from midday to mid-afternoon, drink regularly, and rest and cool down promptly if dizziness, nausea or heavy sweating appear, seeking medical help if needed. Large gaps between air-conditioned rooms and the outdoors can also be uncomfortable.
Mung bean soup, winter melon soup, sour plum drink, watermelon and bitter melon are traditional summer fare, though tradition also cautions against too much iced food. These are general traditions, not medical advice.