Organic gardens may yield more nutrients

PULLMAN – One of the hottest trends in gardening today is organic gardening which relies on natural processes to grow plants. There is now a growing consensus among scientists that organically grown fruits and vegetables may contain higher levels of nutrients than conventionally grown produce.

“Organic gardening is experiencing a surge in interest,” said Tonie Fitzgerald, state Master Gardener program leader for WSU Extension, “and there is more information about doing it correctly.”

Master Gardeners are university-trained volunteer educators who answer garden-related questions, teach gardening classes, and manage demonstration gardens on behalf of county extension offices across the state.

There is no question that organic gardening requires more work. Now there is growing scientific evidence showing that the extra effort may pay off in some nutritional benefits.

That was the conclusion of a panel of scientists at the annual meeting of the American Association for the Advancement of Science this past February in Chicago. The scientists on the panel, which was organized by Preston Andrews, associate professor of horticulture at WSU, and The Organic Center, reviewed a decade of research comparing the impacts of organic and conventional farming systems on soil and food quality.

Among other studies, they cited research that has found that organically farmed tomatoes have higher levels of soluble solids and secondary plant metabolites. Most of the secondary plant metabolites are antioxidants, which help prevent human diseases.

Studies of 27 varieties of organically grown spinach found higher levels of flavonoids and vitamin C and lower levels of nitrates. Nitrates in food can form cancer-causing compounds.

Improved soil chemical and physical properties were seen in apples grown organically in research in Washington. Improvements in soil quality were shown to lead to added nutritional quality, taste, and storability.

Soil is made up principally of mineral particles, organic matter and microorganisms that break down organic residues into organic and eventually inorganic compounds. Organic matter is the residue of decomposing plant and animal material. Organic matter is the fodder for nutrient recycling in the soil, and it also improves soil structure and water retention.

What lessons can home gardeners learn from this research?

“Increase the organic matter content of your soil,” Andrews said. “I think one of the best ways you can do this is with compost. Feed the soil so that the soil microorganisms can provide readily available nitrogen and other nutrients that plants need, but in a more slow-release fashion than synthetic fertilizers do.”

Composting is the managed decomposition of plant and animal material, and is a way of speeding up what happens in the soil naturally. Yard wastes and vegetable scraps, which comprise as much as 20 percent of household garbage, can be recycled in the soil as compost, according to Craig Cogger and Dan Sullivan, authors of “Backyard Composting,” a free WSU Extension bulletin.

“With composting, you get some readily available sources of nitrogen and ammonium because the soil microorganisms produce them as the digest the proteins and then the amino acids that are broken down from the proteins,” Andrews said.

How long will it take to see benefits?

“It depends on the soil you start with and how greedy you are for producing something from the soil,” Andrews said. For depleted soils, he recommends planting a green manure crop, especially legumes which fix nitrogen from the air, then turning it into the soil and letting it decompose before planting a vegetable crop.

“You can add compost along with the green manure crop,” he said. “It really depends on the condition of the soil you start with and what you want to produce from it.”

“Backyard Composting” is available as a free download from WSU Extension at

WSU Extension Master Gardener can provide information on organic gardening and composting. Find one near you at; click on your county.