Shishira ritu – magha, phalguna – approx January 20 to March 20 – bitter taste predominent
Vasantha – Chaitra Vaishakha – March 20 to May 20 – kashaya (astringent) taste
Greeshma – Jyeshta Ashada – ~ May 20 to July 20 – Katu (pungent) taste predominant.
Texts of ayurveda describe uttarayana as aadanakala. In this period sun rays are intense and take out the coolness in air. The atmosphere becomes dry due to evaporation of water molecules. Hence uttaryana is also known as agneya or agni pradhana kala , where fire element is predominant in surrounding environment.
Dry and harsh weather imparts the same nature in animals and plants. Tissues of animals and plants lose the moistness and their strength reduces. Animals, plants and humans feel weak and lose their body weight. The plants become dry and their parts usually taste bitter, astringent and pungent. Consumption of such plants further aggravates the dryness of tissues. Hence ayurveda acharyas advise to follow ritucharya to preserve strength, boost immunity and to keep diseases at bay.