Dustin Choi

Dustin Choi, an employee at medical marijuana processor and supplier Evergreen Herbal in Seattle, shows a cannabis drying rack on Tuesday. (Andy Matarrese / Daily Record)

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Hundreds of groups have applied with the state to grow marijuana under the Washington’s recreational marijuana law. Beyond questions of safety, policy and what it means for public attitudes toward drug use, there’s one other issue that’s especially relevant in water-strapped Kittitas County:

How much water does a pot farm use?

The easy answer? Maybe a bit more than alfalfa, maybe less than corn.

It might sound simple, but comparing water consumption among different crops can be challenging.

Different soil types, irrigation plans and climates affect how many inches of water — inches of water being just one of many measures used — a given crop might need in a year, and irrigators and growers make measurements with multiple methods and in different units.

“There’s just no good way to accurately estimate crop water use,” said Troy Peters, an irrigation specialist with the Washington State University Extension service in Prosser.

To get a sense of outdoor-grown marijuana’s water needs, Botec Analysis Corporation, the think tank contracted by the Washington State Liquor Control Board to provide advice on the weed trade, looked at hops, a plant in the same family as marijuana but a different species.

Hops grown in the Yakima Valley consume about 28 inches of water annually, according to Botec’s report to the state, but that number can exceed 50-60 inches depending on growers and the irrigation method they use.

That comes out to about 300-450 gallons of water per pound of hops, according to the report.

On average, corn in the U.S. uses about 98 gallons of water per pound of crop, according to the Water Footprint Foundation, a Netherlands-based network of global water conservation programs. The global average for a pound of wheat flour is about 238 gallons, according to the foundation’s research.

Watering hemp

Botec also looked at hemp, which is virtually identical to the breeds of cannabis used as a drug. Hemp grown in British Columbia uses about 12-15 inches of water per growing season, according to the report, which added studies in Europe found hemp needs 20-28 inches for optimum yield. The difference comes from climatic and rainfall differences between the two regions, Peters said.

Botec added hemp production usually happens in areas with significant rainfall, and there’s little information on hemp irrigation.

The U.S. Department of Agriculture’s "Washington Irrigation Guide" lists the amount of extra, irrigated water crops need to grow.

Alfalfa grown in the Ellensburg area would need about 30 inches additional water through irrigation. Grapes, 23 inches; sweet corn, 20 inches; apples, 30-38 inches depending on cover; and pasture or turf, 31 inches.

The report uses old data, and Peters said those numbers seemed low for Ellensburg, underestimating watering needs by 10 to 15 percent.

No ‘best practices,’ yet

The state has received almost 60 applications to grow marijuana in Kittitas County, and Michael Graham is one of those applicants. He has plans to build an outdoor growing operation.

He couldn’t give an exact breakdown of how much water his plants might need.

The WSLCB calculates growing space by canopy size. Since medical growers in Washington have been limited by number of plants, estimates for water and other requirements might be less exact, he said.

“We have a long way to go as far as establishing best practices in this industry,” he said. “I think, by default, the commercial growing has been an extension of the black market growing that had developed through the years, mainly indoors.

“Obviously, people wanted to be inside so they wouldn’t be busted.”

A “median expectation” for a mature, flowering, 5-foot plant might be about 2 gallons of water daily, he said.

Growing outdoors or growing larger plants might change that number, he said. Bigger plants and more sunlight would mean more water.

He compared growing cannabis to growing tomatoes.

“Their water and nutrition needs should be similar, and the cultivation technique would be similar,” he said.

Graham estimated he might have one plant per 15 square feet. They need more room outside, he said.

He thinks most growers will hand-water, or use drip irrigation.

“People like to hand-water because they like to have direct control over the water usage of the plant,” he said, and either method ought to limit runoff or evaporation.

He plans to water his crop through Kittitas Reclamation District irrigation water.

“We already have irrigation lines here that irrigate some of the hay on the property,” he said.

Assuming marijuana would have the same growing season as hemp, which likely would have a 30-120 day growing window in the area, according to research from Oregon State University, that comes out to about 840,000 gallons annually on the higher end.

According to the Environmental Protection Agency, a family of four uses about 400 gallons of water in their home daily, or about 146,000 gallons in a year.

Ultimately, Graham thinks growing outdoors will cut operating costs in half, compared to indoor growing.

Indoor growing

Indoor cultivation is water intensive, especially when done hydroponically. An estimate cited by Botec said a 240 square-foot growing room would take about 40 gallons of water per day, or about 98 inches of water per year.

So far, most growers seem fine with staying indoors, according to Brian Smith, a Liquor Control Board spokesman.

Based on a quick check of 260 pending applications, 30 percent are for outdoor grows, he said.

Marco Hoffman — the manager of Evergreen Herbal, which has also applied to grow in Kittitas County — plans on building indoors.

“There’s infinite ways to skin this cat,” Hoffman said.

Hoffman said he expects most of the initial growing operations in Washington will be indoors.

“However, I think that the paradigm has shifted and what you’re going to see moving forward is more traditional commercial agricultural techniques being implemented,” he said.

His plans call for a set of raised soil beds inside a greenhouse, which he said will require less water.

His estimate is 4 million gallons of water annually for every 100,000 square feet of canopy space.

The state originally planned to offer growing licenses for farms up to 30,000 square feet, but since cut the cap to 21,000 square feet. Even at the older, higher number, the largest single farms would have about half an acre, which is about the size of a football field, according to the liquor control board. Applicants can apply for multiple licenses, but can’t hold more than a third of the licenses allotted in one county.

On a 21,000-square-foot field, Hoffman’s estimate, like Graham’s, comes out to about 840,000 gallons of water annually.

Hoffman said the land he hopes to use has a water right.

“With the raised bed system, that water just gets reused. It drains out, it ends up recaptured again and we reuse it again,” he said. “As far as water efficiency, raised beds and hydroponics are much more efficient than planting directly into the soil.

Since growing space is so limited, traditional crop rotation would hurt efficiency. Raised beds would allow growers to easily remove, replace or add amendments to the soil as needed.

He also said not planting directly in the ground will be easier on the soil and environment, because fertilizer won’t leach into groundwater.

“What we’re trying to do is create something that’s very sustainable and is very socially conscious, so the carbon footprint is going to be really small,” he said.

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