Chaturmasya 

Period                                                   Abstain from
July 16 to August 14                          Green leafy vegetables
August 15 to September 13             Yogurt
September 14 to October 12            Milk
October 13 to November 12            Urad dal

The Chaturmasya (four-month) period begins in the month of Ashadha (June-July) and ends in the month of Kartika (October-November). Chaturmasya means "four months", which is the duration that Vishnu sleeps.

Some Vaishnavas also observe Chaturmasya from the full-moon day of Ashadha until the full-moon day of Kartika. Others also observe Chaturmasya according to the solar month from Shravana to Kartika. The whole period, either lunar or solar, takes place during the rainy season. Chaturmasya should be observed by all sections of the population. It does not matter whether one is a grihastha or a sannyasi. The real purpose behind the vow taken during these four months is to minimize the quantity of sense gratification.

In the month of Shravana one should not eat spinach, in the month of Bhadra one should not eat yogurt, and in the month of Ashvina one should not drink milk. One should not eat fish or other non vegetarian food during the month of Kartika. A non vegetarian diet means fish and meat. Similarly, masur dhal and urad dhal are also considered non vegetarian. These two dhals contain a great amount of protein, and food rich in protein is considered non vegetarian. On the whole, during the four-month period of Chaturmasya one should practice giving up all food intended for sense enjoyment.

– A.C. Bhaktivedanta Swami Prabhupada,
Sri Chaitanya Charitamrita, Madhya-lila 4.169

During festivals of the Lord (i.e. Balarama Purnima, Sri Krishna Janmashtami, Radhashtami, etc) all preparations are offered to the Lord and Chaturmasya vrata of restrictive honouring of even foods in the above categories does not apply.

The observance of Chaturmasya regulations is often described in the karma kanda (ritualistic performances for material fruitive benefit) portion of the Vedic scriptures. Devotees follow the Chaturmasya vrata not for any material benefit, but only for enhancing their devotional service to Krishna.

In the karma-kanda section of the Vedas it is said, apama somam amrta abhuma and aksayyam ha vai caturmasya-yajinah sukrtam bhavati. In other words, those who perform the four-month penances become eligible to drink the soma-rasa beverages to become immortal and happy forever.
– Bhagavad-gita, 2.42

Chaturmasya-vrata

In the Vedas it is said that one who observes the Chaturmasya-vrata will attain eternal happiness in the heavenly kingdom. One who performs the Chaturmasya-vrata becomes pious. By becoming pious, one may be promoted to the higher planetary systems. In the Bhagavad-gita, it is said that this flowery language of the Vedas mostly attracts persons who identify with the body. To them such happiness as that of the heavenly kingdom is everything; they do not know that beyond that is the spiritual kingdom, or kingdom of God.

Purpose of Chaturmasya-vrata

Sannyasis are generally meant to travel all over the country for preaching work, but during the four months of the rainy season in India, from July through October, they do not travel but take shelter in one place and remain there without moving. This non movement of the sannyasi is called Chaturmasya-vrata. When a sannyasi stays in one place for these four months, the local inhabitants of that place take advantage of his presence to become spiritually advanced.

During these four months, saintly persons who are accustomed to travel from one place to another to propagate Krishna consciousness remain at one place, usually a holy place of pilgrimage. During these times, there are certain rules and regulations which are strictly followed. It is stated in the Skanda Purana that during this period, if someone circumambulates the temple of Vishnu at least four times, it is understood that he has travelled all over the universe. By such circumambulation, one is understood to have seen all the holy places where the Ganges water is flowing, and by following the regulative principles of Chaturmasya one can very quickly be raised to the platform of devotional service.

Below is a list of food items that should not be consumed during the Chaturmasya period:

Month Fasting From Items to be avoided Exceptions
Shravana
(July 16 to
August 14)     
Shak Red and Green Spinach. All varieties of Shak (Green leafy vegetables) Coriander Leaves, Methi Leaves, Pudhina and Curry leaves. However, Cabbage can be taken as it is not Shak.
Bhadra
(August 15 to
Sept. 13)
Curd / Yogurt Any item in which curd is the major ingredient: Kadi, Pacchadi, Butter milk, Lassi, etc. If little curd (two or three spoons) is added in Sabji to get taste, it will not break the vow. Charanamrita should be honored even if it contains curd in it.
Ashvina
(Sept. 14 to
October 12)
Milk Any item in which milk is the major ingredient: Sweet Rice preparation using milk, Milk Shakes, Ice Creams, Condensed Milk, etc. Milk Sweets (like Peda, Rasagulla, Sandesh), Milk products (like Paneer, Cheese) since milk is transformed and used. Charanamrita should be honored even if it contains milk in it.
Kartika
(October 13 to
Nov. 12)
Urad Dhal Idli, Dosa or any other preparation containing Urad Dhal should not be taken.