With organic produce sales topping $43 billion last year, stocks of organic seed are struggling to meet demand.

The U.S. Department of Agriculture does not require organic farmers to use organic seed if supply is short.

A new report from the Organic Seed Alliance shows that large organic farms are only using 20 percent organic seeds, while small farms with less than 10 acres are still using 75 percent organic seed.

Overall, more than 30 percent of the farms surveyed said they use more organic seed today than three years ago.

The report collected data from more than 1,300 farms and 16 seed companies.

Its authors called for more public funding for training to boost organic seed production.

Read More:

• A Missing Puzzle Piece For Farmers: Organic Seed (Civil Eats)
• State Of Organic Seed 2016 (Organic Seed Alliance)