After WWII, there was an initiative to develop alternative uses for fission energy. It was called Atoms for Peace and part of it included atomic gardening. Gamma gardens, as they are known, were created in the US, India, Japan, Europe and Russia to study the effects of radiation on plant life.
The gardens were built in the shape of a cartwheel and covered about five acres. They were surrounded by an eight metre high dyke to prevent the radiation spreading outside the garden. At the hub of the wheel was the radioactive material, either Cobalt -60 or Caesium-137.
The wheel was planted with different plants which were left exposed to the radiation for seven to eight months. The plants closest to the radioactive source usually died, the ones a bit further out developed tumours and were misshapen but the plants furthest away mutated and produced new usable plants.
The Rio Star grapefruit and a strain of peppermint resistant to verticillium wilt was developed in this way. Many of the mutations developed went into commercial production (Rio Star grapefruit account for 75% of Texas' grapefruit crop) and are still grown today.
The Atomic Gardening Society was started in 1959 by Briton Muriel Howorth, an atomic activist. The society distributed irradiated seeds to keen gardeners who were supposed to report back on the results. Interest faded in the 60s as gardeners' feedback was sporadic and enthusiasm waned.