CHARLIE NEUMAN / Union-Tribune Teresa Fiske and Robert Hahn turned their 3.5-acre, 400-tree Hass avocado grove into an organic growing project that produces thousands of pounds of the fruit each harvest.

And Hahn should know: He and his wife, Teresa Fiske, 51, have converted their 3.5-acre, 400-tree Hass avocado grove into an organic growing project that produces thousands of pounds of the fruit each harvest. They sell them online at organicavos.com.

“What's unique about our approach is that we have a positive impact on the environment on a micro level,” said Hahn, 60.

The California Avocado Commission lists the Hass avocado variety as the state's most popular, accounting for 95 percent of avocados produced. Hahn said the variety generally produces 8-ounce avocados, with thick, slightly pliable skin and a creamy texture.

Hahn grew up in Omaha, Neb., and graduated from the University of Pennsylvania in 1970 with an independent degree he designed to incorporate chemistry and biology. From there, he participated in several sustainable organic growing projects, running a soil lab in New Mexico and helping design Biosphere 2, an enclosed ecologic system research center in Arizona, he said.

CHARLIE NEUMAN / Union-Tribune The Hass avocado accounts for 95 percent of avocados produced in California. The variety generally produces 8-ounce avocados, with thick, slightly pliable skin and a creamy texture.

Fiske grew up in a military family that moved frequently. She graduated from Colorado State University with a bachelor's degree in computer science; she also earned a bachelor's degree in music from the University of Arizona. She acquired her affinity for plants from gardening with her mother.

When Hahn and Fiske moved to Bonsall in 1994, they registered the avocado trees already existing on their new property with the state and listed their intention to convert the orchard to an organic grove, Hahn said.

Some examples of their organic growing practices:

They forgo chemical-based pesticides to eliminate mites. Instead, they turn green lacewing insects loose in the orchards, Hahn said. Although adult lacewings feed on pollen and nectar, their larvae have a hearty appetite for mites and other insects.

Instead of chemical fertilizers, Hahn and Fiske use an organic, fish-based fertilizer approved by the Organic Materials Review Institute, a nonprofit organization that lists which products can be used in organic production.

Rather than use chemicals to kill weeds, they remove weeds by hand and use wood chips from their own stumped trees to discourage further growth.

“The idea is not only to use less pesticides and chemicals that are potentially harmful, but also to use our surrounding areas,” Fiske said. “That really keeps a reliance on natural resources. It's healthier.”

During harvest time, workers use a picking pole with a cutter to slice avocados from the trees, Hahn said. They cover the picked fruit so it doesn't sunburn and develop black spots that prevent the avocado from ripening evenly.

“We're concerned about quality,” Hahn said. “The top line and the bottom line. We need to make money, but we are as concerned about the quality of the product as we are in making it economically viable.”

Harvest season is March through August, with July as the peak, Hahn said. A good harvest might yield about 10,000 pounds of avocados per acre. The avocados take six to nine months to grow.

They are sold three ways: to local markets such as Jimbo's, a natural foods grocery chain; to packing houses; and to individuals who place orders on the couple's Web site at $2 per avocado, Hahn said.

Hahn and Fiske prepare avocados in their own kitchen, too: They grind the fruit to make guacamole, combine it with grapefruit to top salmon dinners or just sprinkle it with salt and pepper.

Fiske said she also prepares desserts such as avocado cheesecake and avocado mousse.

Will Walker, a Pennsylvania investor, found Organic Avos online four years ago when searching for a reliable source of organic avocados, he said. Walker orders about two dozen avocados each month for his family of four.

“We use them in salads, we smash and spread them on bread instead of mayonnaise, we make a lot of guacamole, or eat them totally raw with nothing else,” he said. “We just love them. I'm kind of an avocado snob, and I've never found a better avocado.”

 Emily Vizzo is a freelance writer from La Jolla.