The Royal Horticultural Society (RHS) has revealed the winner of the Windlesham Trophy.
For the past 26 years, the award has been given to the prison with the best garden in England and Wales.
It is named after the former chairman of the parole board Lord Windlesham, who set up the competition in 1983.
He felt the award would give prisoners something to work towards and evoke a sense of pride, the body revealed.
This years winner was east Yorkshires HMP Everthorpe, which beat Suffolks HMP Sudbury by one point.
Commenting on the award ceremony, governor Susan Morrison said the success was brought about by a years worth of work.
"Our visitors were impressed, not only by the lovely and imaginative gardens, but also by the general cleanliness of the prison, the helpfulness and enthusiasm of the staff [and] the positive atmosphere around the prison," she told the RHS.
In other news, Cambridge University will give greenhouse enthusiasts a peak at its gardens during three open days next month to celebrate its 800th anniversary.