The project, led by University of Leeds professor of nutritional epidemiology and public health Janet Cade, will evaluate the campaign over two growing seasons. Results will be released in 2012.
The RHS launched the campaign in 2007 to help children develop life skills through gardening. It now has 11,500 schools gardening. By 2012, the RHS wants 80 per cent of primary schools gardening.
Jim Bliss, the campaign's London adviser, will be helping schools in the study. "I have seen for myself the dramatic results gardening can have on pupils," he said. "They are so proud when they have successfully grown potatoes or beans and are fascinated by wildlife. Every school should have a garden, no matter how big or small."
A total of 74 schools across the capital will be taking part in the study to look at the eating habits of pupils aged seven and eight.
Researchers will see whether growing food through school gardens plays a role in the amount of fruit and vegetables children eat and their other food choices, such as snacks and soft drinks.
Over two years the schools will be visited regularly by Cade's team. "On average, children eat two-and-a-half portions of fruit or vegetables each day," he said.
"This falls well below Government recommendations of five portions a day and our aim is to get closer to this goal."