The subscriptions can be deposited in lumpsum or in convenient installment of not more than 12 installments.
It completely depends on you as how you want to invest in PPF.
It is not necessary to deposit subscription in every month of the year. The amount of subscription can also be varied to suit the convenience of the subscriber.
The minimum subscription in the PPF account per year should not be less than Rs. 500 and it cannot exceed Rs. 100000 in a financial year. The subscription may be paid into account in one lump sum or installments not exceeding 12 in a year and the installments are to be in multiple of Rs. 5.