During the early 1960s, garden shows in the United Kingdom and the United States had more than your average plants. There were huge peanuts, there were a large number of tomatoes growing on a single branch, and there were seeds that promised exceptional qualities. It was a time when home gardeners and lab researchers alike indulged in the craze of “atomic gardening” by bombarding the plants with radiation and then crossing their fingers for a favorable genetic mutation. Several of their experiments even yielded crops that we now enjoy every day, including peppermint and the ruby red grapefruit.

Popular during the 50s and 60s, atomic gardening is a form of mutation breeding in which plants are exposed to radioactive material, like cobalt-60, to create useful mutations. They were a part of Atoms for Peace, a program for peaceful fission energy after World War II which gradually turned towards plant mutation. 

Atomic gardens, also known as “gamma gardens,” were established in laboratories in the United States, Europe, India, Japan, and parts of the former USSR. They were initially designed to test the effects of radiation on plants. The research gradually turned towards using radiation to introduce beneficial mutations for useful characteristics such as increased resilience to adverse weather, or a faster growth rate. In 1959, an atomic activist based in the United Kingdom, Muriel Howorth, established the Atomic Gardening Society. The society employed an early form of crowd-sourcing, in which members received irradiated seeds, planted them in their gardens, and sent reports.

Inspired by Howorth, over 300 gardeners soon started experimenting in the UK. In the US, an oral surgeon and gardener named C.J. Speas turned the concrete bunker in his backyard into a radioactive experimental lab. He soon became one of the leading sellers of irradiated seeds, including that of radishes, sweet corn, and tomatoes to the public.

Gamma gardens were usually five acres in size and were arranged in a circular pattern with a retractable radiation source in the center. Plants were usually laid out like slices of a pie, each plant receiving varying amounts of radiation along the radius.

The gamma garden operated on a simple mechanism. A radioactive, isotope-laden metal rod was placed in the garden’s center. Radiation slowly bombarded the plants’ DNA like a hammer and would change how genes were expressed. The largest, usually lab-based, gamma gardens could span up to five acres, with plants arranged in sections like a pizza or a pie. One such Gamma Field is in Hitochiomiya, about two hours northeast of Tokyo, opened by Japan’s Institute of Radiation Breeding in 1962.

The plants closest to the radioactive source died, and those a little further grew tumors, but the ones farther away showed mutations. Over two thousand new varieties of plants, most of which are now used in agricultural production, were created, including today’s peppermint and red grapefruit. 

For around twenty hours a day, plants were bombarded with radiation, after which scientists wearing protective equipment would enter the garden to make assessments. The plants that were the plants of interest had a higher than usual range of mutations, though not as damaging a dose as of those closest to the radiation source. According to Dr. Lagoda, the head of plant breeding and genetics at the International Atomic Energy Agency, radiation breeding has produced thousands of useful mutants. A sizable fraction of the world’s crops which were judged to be genetically better were also achieved.

They include varieties of rice, wheat, barley, pears, peas, cotton, peppermint, sunflowers, peanuts, grapefruit, sesame, bananas, cassava, and sorghum. The disease resistant peppermint plant and the “Rio Star” grapefruit, which accounts for 75%t of the grapefruit production in Texas, were created in these atomic gardens.

With the shift of political climate away from atomic energy and a failure of crowd-sourcing in producing any noteworthy results, the Atomic Gardening Society declined by the mid-1960s. Soon, modern genetic engineering has replaced atomic gardening.

In spite of the decline, large-scale gamma gardens remained in use for a long time. A number of commercial plant varieties were also developed and released by laboratories as well as private companies. Japan’s Institute of Radiation Breeding still runs a Gamma Room and a Gamma Greenhouse, where more potent doses of radiation or more targeted techniques are used. The circular garden measures 100 meters in radius and is enclosed by an 8-meter-high shielding dike wall. There, hundreds of mutant varieties were developed including the black spot disease-resistant Gold Nijisseiki pear.

[sources: Wikipedia, AtlasObscura, AmazingPlanet]