Police said the deceased, identified as Parvathy, and Nagavalli, both aged 45, used to work in the garden from morning till evening and return together to their respective houses.
Nagavalli found Paravathy missing on June 6 and informed her relatives. Paravathy's body with frothing at the mouth was found near a haystack in the garden while Nagavalli later fainted and died the same day.
Post-mortem revealed Nagavalli died due to poison.
Parvathy's body was cremated by relatives who thought that she could have been bitten by a snake.
But it was not known whether they were bitten by some poisonous creatures or their food was poisoned.