It believes medium-sized box schemes could be hardest hit through a combination of increased competition from significant players such as Riverford Organic Vegetables and Abel & Cole, as well as the economic downturn.
"They have a smaller core of fiercely committed customers than the smallest schemes and yet they lack the kind of marketing resources that the bigger players have to pull in new business," it said.
The report added that price comparisons over the past year show organic fruit and vegetables from box schemes are consistently cheaper than supermarkets.
Alan Schofield, who runs the UK's longest-running vegetable box scheme, Growing with Nature, said business had slowed over the past two years due to crops lost through bad weather and the recession.
"Over the past year, it has been harder to find new customers - with the response to our leaflet drops at an all-time low," he said. "Some customers who are looking to save money see our weekly box of vegetables as a saving that can be made despite the fact that our produce is better value now than ever before."
Vegetables account for the highest proportion of spend on organic products, at 16.3 per cent. UK organic area down to vegetable crops has steadily increased, with allium and root crops standing at over 2,000ha in 2008, potatoes at 2,550ha and green vegetables, salads and protected crops at 4,000ha.