Prisoners inside a Victorian jail have been foiled in their attempts to grow marijuana in a vegetable patch.

A crop of 28 cannabis plants was discovered flourishing this week in a house at Fulham Correctional Centre, a medium security prison about 200km east of Melbourne.

Prisoners have been growing marijuana inside a Victorian jail. Credit:Theresa Ambrose

Some of the plants were up to half a metre tall, the state's correction's boss said, and was growing alongside plants cultivated as part of a prisoner horticulture training program.

"It is embarrassing; these things shouldn't happen inside a prison," Corrections Commissioner Jan Shuard told radio station 3AW.