(This story has been updated to revise the definition of a Tier 1 mixed-light grow.)

While outdoor grows abound in California’s adult-use market, the state’s supply of recreational cannabis is dominated by indoor and greenhouse producers in Santa Barbara and Humboldt counties.

According to licensing data released by the California Department of Food and Agriculture, 1,192 of the 2,906 recreational cultivation licenses issued throughout the state – or 41% – were for outdoor grows.

Relative to indoor and greenhouse facilities, the production capacity of outdoor growers is limited.

They can harvest only once a year, and yields are generally lower given their complete reliance on Mother Nature to maintain temperature and control lighting conditions. Indoor and greenhouse growers, by contrast, are able to harvest multiple times a year.

Onerous regulations or outright bans on outdoor cultivation sites by many California counties also have made it harder for outdoor grow operations to expand their footprints.

Of the 26 counties in the state that have issued cultivation licenses to date, 14 haven’t awarded any to outdoor growers.

More than half of all cultivation licenses issued in California went to businesses in two counties: Santa Barbara and Humboldt, both of which allow outdoor grow sites. Those counties account for approximately 42% of the state’s total production capacity.

Santa Barbara County is also home to 13 of 20 of the largest cultivation operations in the state, with the average licensee holding nearly 13 grower licenses – well above the average of 1.4 licenses per licensee throughout the rest of the state.

According to Kristin Nevedal, chair of the International Cannabis Farmers Association – a trade group that promotes sun-grown cannabis – Santa Barbara County has been a hotbed of cultivation activity because of the large amount of available greenhouse space.

“We’ve seen cultivation really blow up because those facilities are plug-and-play, ready to roll,” Nevedal said. “They have discharge lighting, they have curtains and plenty of square footage.”

Mixed-light facilities are generally how California describes greenhouses, though it also includes outdoor growers using light deprivation techniques. The Tier 1 and Tier 2 distinctions indicate the amount of wattage per square foot used to light the grow:

Tier 1 mixed-light facilities use 0 to 6 watts per square foot while Tier 2 mixed-light facilities use 7 to 25 watts per square foot.

Tier 2 mixed-light facilities are generally enclosed, automated greenhouses that use high-intensity lights to assist in the flowering process.

Tier 1 mixed-light facilities can be seasonal, open-air greenhouse structures that use artificial lights as a supplement to the sun, or outdoor grows utilizing tarps or other mechanisms to block sunlight from plants. In either case, these grow operations consume less energy than a Tier 2 mixed-light grow.

Indoor grows are the most energy-intensive type of cultivation operation, using no natural sunlight and consuming more than 25 watts per square foot.

Estimated annual production capacity was derived as a function of maximum cultivation space, estimated yield per square foot and estimated harvests per year for each type of cultivation license.

Average yields of 30 grams per square foot were projected for indoor and tier 2 mixed-light facilities, and 20 grams per square foot for outdoor and Tier 1 mixed-light facilities.

It was assumed that outdoor cultivators would harvest once a year, while Tier 1 mixed-light growers would harvest an average of three times per year and indoor and Tier 2 mixed-light growers would harvest an average of five times per year.

Eli McVey can be reached at [email protected]

Maggie Cowee can be reached at [email protected]