Costco has a voracious appetite for organic fruits and veggies — so much so that it can't get enough of them to sell.

The warehouse retailer recently passed $4 billion in annual sales from organic produce, eclipsing Whole Foods for the title of organic heavyweight champion in the U.S. Now, organic farmers can't grow produce fast enough to supply the retailer.

To help nudge supply in the right direction, Costco is lending money to farmers, allowing them to buy land and equipment to grow more organic produce.