By Sally Brown, University of Washington

Abstracts of these resources are available in the searchable Information Portal offered to Northwest Biosolids members.

  1. Legal cannabis laws, home cultivation, and use of edible cannabis products: A growing relationship?

  2. The quasi-legal challenge: Assessing and governing the environmental impacts of cannabis cultivation in the North Coastal Basin of California

  3. The carbon footprint of indoor Cannabis production

  4. The Benefits of Growing Cannabis with Compost

  5. The Genesis of a Critical Environmental Concern: Cannabinoids in Our Water Systems

I decided to end the year on a high note (pun intended).  This month’s library takes us into the great and expanding unknown.  I am not talking about black holes here- rather the realm of kush aka cannabis.  I will dispense with trying to sound cool for the rest of the library.  It is way too much of a stretch.   

As of writing this library summary, cannabis is legal for recreational use in 10 states, 7 of which tax purchases in retail stores.   If you consider states where medical use is legal- the majority of the country is included. Canada - that big progressive country up north went full legal just recently.











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Legalization has taken an industry that has been operating under cover for decades and brought it- or is working to bring it to light.  Cannabis sales in Washington State in 2018 totaled $534 billion with excise tax revenues of over $120 billion (  That is a lot of material and a lot of money.  The point for this library is that growing this material is a potential huge market for biosolids and composts.  How big and how best to enter it are questions that remain to be answered.

The library has typically focused on peer reviewed research.  Because cannabis is still illegal on a federal level the agronomic research as has been done for just about every crop, with associated extension bulletins is completely lacking.  Land grant universities rely on federal funding and federal funding essentially prohibits any research on banned substances.  While the peer reviewed literature didn’t turn up anything on growing cannabis in biosolids- it did provide some insight on the industry that can help in figuring out the best ways to enter this market.

Home growers
The first article reports on a survey of growers.  Here the authors went to Facebook to distribute their survey.  They got responses primarily from men (76.4%) and found that a significant number across all surveyed had grown their own (56%).  The survey included respondents from states where laws range from fully illegal to home cultivation allowed to home cultivation + dispensaries are legal.  A significant number of those who had grown in the past were still growing and again- this went across the legal spectrum.  Of those that grow about half throw out their leftover plant material while the other half compost it.  What this article tells us is that there is a significant market for growing materials for the home or hobby grower.  There is also likely a significant market for compost feedstocks from those growing operations. 

Environmental impacts
It may be a hobby for some- but it is more than scraping by for others.  The cannabis industry is big business with associated environmental impacts.  As legal cultivation is a relatively new phenomenon we can look at Northern California for an understanding of what is involved in growing grass.   Humboldt and Mendocino counties were the center of cannabis cultivation.  It was believed before the legalization revolution really got underway, that CA growers supplied up to 79% of the pot consumed in the US (article 2) and most of it was grown in these counties.  When cultivation was illegal, much of it took place on federal or state forest lands.  Growers would clear parcels and grow on hillsides and in the woods.  Article #2 provides anecdotal information on the environmental repercussions of outdoor growing operations.  Impact to water quality as a result of unrestricted use of fertilizers and pesticides is discussed as are carbon emissions associated with clearing trees and planting weed.  The authors note that the high irrigation water requirements for cannabis cultivation in this region meant illegal use of fresh water diverted from streams.  That illegal water use has resulted in some of these streams going dry.  Illegal growing outdoors without the benefit of regulation has had big and bad environmental impacts.  The article includes many quotes and information from the grey literature- again showing it is hard to write science about stuff that is going on below the radar.  

The third article provides an evaluation of energy use for indoor cultivation.  Growing illegally outdoors may suck for the environment- but indoor growing isn’t exactly carbon friendly.  The article goes through the various aspects that use energy for indoor cannabis cultivation.  See figure 1 below.

energy input

It turns out that lighting (33%), ventilation and dehumidifiers (27%) and air conditioning(19%) account for most of the energy use.  The article, from 2012, estimates that indoor cannabis production used 3% of California’s total electricity or 1% of the electricity used in the US as a whole.  That is about as much power as is used in 1 million CA homes.  Production and distribution of cannabis resulted in emission of 15 million tons of CO2 or about 3 million cars’ worth.  You know how 1 ton of food scraps diverted from landfill to compost gives you about a ton of CO2 credits?  Well each kg of cannabis produced emits 4.3 tons of CO2.  So illegal outdoor cultivation is an environmental disaster and indoor cultivation is an incredibly high user of energy. Here is a comparison in MJ per $1000 of product of different crops:

energy compare

The authors of this 3rd article argue that outdoor cultivation can produce as high quality a product as indoor cultivation if done properly.  They also argue that much of the energy used for indoor cultivation is above and beyond what is needed.  

What do we know?
So now in most places cannabis cultivation is legal.  Growers range from individual hobbyists to professionals.  Growing operations take place outdoors and in greenhouses.  In both cases- growing cannabis has been terrible for the environment.  To me this means that these growers need us!  The 4th article in the library is from    Not sure if you need to take the SATS to get admitted there.  It is all about the benefits of growing cannabis with compost.  Read this and you realize how much potential there is for growth and compost use in this sector.  And how little you would learn as compost professionals from enrolling at Cannabis U.  

Avid readers of the Biobull might remember a study that we did with hemp.  Looks and smells like the real deal but with lower THC content.  We tested Tagro and Tagro + char against Happy Frog- a growing media popular in Humboldt, CA.  We got an exceptional response.  The Happy Frog plants are on the right. 

growth trials

growth trials 2

After that piece was published in the Biobull Tagro got an order for 800 yards from a grower outside of Ellensburg and two phone inquiries from other growers.  They were sold out and so couldn’t provide the material.  According to Dan Eberhardt a number of smaller growers come into the plant to buy their Tagro.  The staff have heard that the Tagro works great.

It would seem that these growers would like to ‘grow green’.  There are no organics standards for cannabis cultivation.  It seems like high time (there I go again) to develop products that specifically target these growers.  Ask compost producers in Northern California what it takes to enter a market.  Look at the resources for your state where it is legal to identify growers to partner with.  This is a growth industry that needs to grow greener.  Let us help.

Finally - the last article in the library is just the nonsense that we’ve come to expect.  It is a recent article from Environmental Science & Technology- a high profile journal that loves crying wolf.  The article talks about expanding cannabis use and pharmaceuticals derived from cannabis that are entering the market.  These compounds- the article cautions will and are already entering our nations’ wastewater systems.  They present a potentially dangerous new class of pharmaceuticals and by products that could pose a risk.  The authors detail the chemical structures of these compounds and discuss why we need to worry. 

Don’t let this bring you down.  It is just the normal stuff that we have to deal with.  At least it may get people’s minds off of PFAS.  In the meantime - start thinking about this great opportunity and hope you have a lovely holiday.  See you in February.