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Spent peppermint and spearmint hay left over after distillation is finding good use in several Washington State organic fruit orchards.

The compost, which sells for $25 a ton, is processed and supplied by Royal Organic Products LLC, a subsidiary of
U.S. mint handler A.M. Todd Flavors & Ingredients.

"We recognize that the big push out there is sustainability in agriculture," said Thad Schutt, business manager for Royal Organic Products in Royal City, Washington. The product is on the approved materials lists of both the OMRI (Organic Materials Review Institute) based in Eugene, Oregon, and the Washington State Department of Agriculture’s organic program.

Even though the mint is not grown organically, it is accepted by the industry as an organic input, Schutt said, just as cow manure doesn’t necessarily have to come from cows fed an organic diet.

Mint compost, which is dark in color and virtually odorless, is fairly high in nitrogen and potash, Schutt said. Several necessary trace minerals are also present. The nitrogen, phosphorus, and potassium levels are, respectively, around 2.0 percent, 0.8 percent, and 2.8 percent. Schutt said that mint compost is high in potassium salts and low in sodium salts. The compost is analyzed for several nutrients on a regular basis through the U.S. Composting Council’s Seal of Testing Assurance program.

Adding the material to the soil increases the organic matter, improving water retention and allowing growers to use less water, Schutt said.

At this time, Royal Organic Products is selling only bulk mint compost but is looking into bagging it in the future.

Excellent harvest

Brian Talbot, who manages Columbia Orchards in Sunnyside, Washington, said he has only used the compost for one year on his transitional organic apples, but had an excellent harvest, with good yields, size, and tree growth.

Talbot began banding several varieties of high-density trellised apple trees with mint compost in the fall of 2006. They applied it in the fall of 2006, in the spring of 2007, and applied a "heavy shot" in the fall of 2007"

Talbot said that when nitrogen levels are too high, as they are in chicken manure, it prevents red apples from reaching optimum color.

He added that animal manures are lacking in trace –elements because the animals remove most of them for their own use.

At first, the mint compost was hand-applied with shovels out of buckets to weaker trees. That approach was soon scrapped, however, for a much more efficient one that treated all trees. The compost is banded in four-foot-wide strips down the tree rows.

"We bought a Whatcom spreader that cost us around $20,000," he said, "but it has been wonderful. Now, we’re just blanket-applying everything."

So that the nutrients will reach tree roots sooner, Talbot also uses a Wonder Weeder to till the compost into the ground.

Cost

While Columbia Orchards is now actually spending more money on fertility, –Talbot said the cost per bin has decreased because of better yields. He said that his yields were around 50 bins an acre in 2007, compared with 30 bins in the same block in the previous year. "There would have been an incremental increase anyway, but we were expecting 40 bins an acre."

In 2007, cherry trees were added to the program. In his cherry blocks, Talbot found that the mint compost gave a healthy boost to former Bing trees top grafted to Chelan.

"We had more growth on those grafts than I’ve ever seen. Cherries are hard to graft. We had around 75 percent take, but what did take we had 10 and 12 feet of growth. I’ve never seen that before."

Yield

Zirkle Fruit, Selah, Washinton, began banding mint compost down its organic apple and cherry tree rows four years ago. It also uses the compost in wine grapes.

"We’re using it fairly widespread into our conventional plantings as well," said Orchard Administration Manager Harold Austin.

He cites several reasons for the switch to mint compost:

"We don’t have the salt concerns that we would have if we were using composted manure. We are getting very good organic matter to help with soil microbial activity, plus [good] water retention."

Austin said that so far it’s been hard to define any yield increases. What he’s not seeing is the yield decreases expected when switching from conventional to organic orchard management, he said,

While still incorporating some animal byproducts and compost teas into his nutrition program, Austin said he’s "gone very aggressively to mint compost."

He added, however, that mint compost "is just one piece of the nutritional –puzzle."