There has been an assumption made that cannabis growers are now responsible for the destruction of the Eel River watershed. However, we all know the Eel River was on the most endangered rivers list long before cannabis cultivation had any impact. Now, due to the drought, cannabis needs to be evaluated the same way all agricultural crops are evaluated.
In comparison with other agricultural crops, cannabis does use a good deal of water. It is current opinion that cannabis cultivation should be limited based on water consumption.
The Humboldt Growers Association (now Emerald Growers Association) proposed an ordinance in 2010 stating that “marijuana used an average of 22.7 liters (6 gallons) of water a day.” The statistics in that report on gallons used per day per plant were overstated (Emerald Growers Association no longer supports these statistics.). Now they have been referenced again in the Bauer report “Impacts of Surface Water Diversions for Marijuana Cultivation on Aquatic Habitat in Four Northwestern California Watersheds.” Neither of these accounts takes into consideration water consumption in relation to total biomass. The square foot assessment does not account for the variation in water consumption per square foot relevant to the average height of a plant or garden. This will result in gross overestimates of water consumption and a reduction in production allowed by the county and or state.
A CURRENT ACCURATE CANNABIS WATER USE STUDY IS NOT YET ON RECORD. This paper will show that crops need to be measured volumetrically in gallons/day/pound if we are to be able to analyze the impact of cannabis on the water supply. Humboldt Growers Collective encourages all growers from Humboldt to submit to Humboldt Growers Collective their own water studies so that we may begin building a database of pertinent water information for our county.
Our current accepted system of growing cannabis encourages growers to remain at peak water consumption during the months that the aquifer is most in danger of collapsing.
Our hypothesis is that if we grow more and smaller plants while finishing them over a shorter life cycle, we can greatly reduce the total number of gallons it takes to grow a pound of cannabis. Further more, cannabis does not need to be grown during the dry months at all.
More plants per square foot = a shorter life cycle = less total water used per pound grown.
This study compares two gardens over a 5 year period from 2010-2014. We are presenting results as the 5 year average. Our test groups were a contrast of two very different growing techniques. Our prediction was that we could ascertain the high and low rates of cannabis water consumption. Our intent is to present these findings as a way to navigate the “cannabis water use issue.”
The various coefficients considered were:
– soil volume/surface area ratio: what is the ratio of soil, to surface area, to water consumption, to pounds yielded?
– soil density: does the soil contain a wetting agent? how does it distribute(utilize) the water?
– type of containment: what percentage of water is lost? what percent actually gets used by the plant?
– seed starts vs clone starts: Is there an advantage to one over the other?
– total area occupied by a “unit”: The subject unit varies in size between the two groups. the question is.”how many cubic feet does a pound of cannabis require?”
– water application and distribution: how is the water distributed?
– equilibrium: is the plant taller than it is wide? do plants proportions affect its metabolic rate?
– evapotranspiration ratio: larger plants evaporate and transpire more than smaller plants. do they do it as efficiently?
– plant hydraulics: amount of energy expended in pumping action per vertical inch of plant mass.
– production biomass vs. support biomass ratio: what percent of the total plant mass is “produce”? what percent of total mass is there to support the produce?
– harvest process: how laborious was the harvest process?
– product quality: does it decline in relationship to the plant’s overall biomass?
For our control group, we used the current model supported by the state, county and local environmentalist groups. Current belief is that this system will effectively limit cannabis cultivation and therefore water consumption. The emphasis on this system is on low plant count. This encourages the grower to run crops “full term” in hopes of maximizing yields, encouraging peak water consumption during the most impacted months.
This control group is the “Traditional 215” outdoor method, involving full term plants, 6 feet tall, with 99 plants in a garden. These plants are caged and tied vertically. We used the following equation to determine the control group’s consumption :
Total gallons/180 days = x / total yield = gallons/day/pound.( x = the average number of gallons consumed per day)
The particulars of this method are listed below:
– 6 month crop: beginning April 15th and ending October 15th
– 100 gallon pots on 12 ft. centers. total area of garden: 14400 sq. ft.
– 100 gallons of soil with wetting agent (surface area 12 sq. ft.) (8.3 gallons of soil per sq. ft. of surface area)
-1 clone per pot on 12’ ft. centers. (each unit area taking 144 sq. ft.)
– water was administered by hand with a hose. Exact bed by bed measurements were taken.
For our test group, we chose the most efficient system we could find. The parameters in this system are open-ended. This encourages the grower to run the most efficient crop they can. It allows the grower to get similar yields without growing during the dry season when the aquifer is at its low point.
This test group is based on the greenhouse light deprivation method involving short term clone plants, 3 feet tall. These plants are woven through a horizontal trellis netting system. We used the following equation to determine the control group’s consumption :
– Total gallons/90 days = x divided by total yield = gallons/day/pound.(x = average gallons consumed per day)
The particulars of this method are listed below:
– 3 month crop: beginning April 15th and ending July 15th
– 5’x5’ beds 8” deep. total area of garden: 4000 sq. ft.
– fully lined and contained beds
– 150 gallons of soil with wetting agent (surface area 25 sq. ft.) (6 gallons of soil per sq. ft of surface area)
– 6 clones per bed with 3 ft isles. (each unit area taking up 40 sq. ft.)
– water was administered by hand with a hose. exact bed by bed measurements were taken.
The first graph below charts the weekly water consumption per container for the term life of the control group.. The vertical axis is gallons used per week, while the horizontal axis is a week by week timeline.
Grow Period from April 15th to October 15 (approximately 180 days)
Total number of gallons used is 787 / 100 gal container / over 180 days
average yield was 2.5 pounds per container.
The second graph below charts water consumption per bed for the term life of the test group. The vertical axis is gallons used per week, while the horizontal axis is a week by week timeline.
Grow Period from April 15th to July 15 (approximately 90 days)
Total number of gallons used is 315 / 150 gal bed / over 90 days
average yield was 2.0 pounds per 25 sq. ft. bed.
– used 787 gallons per plant (unit)
– yielded 2.5 pounds per plant
– it took 315 gallons of water to grow one pound
– it used 4.375 an average gallons of water a day per plant (unit)……..It was not 22.7 litres or 6 gallons.
– it took 1.75 gallons a day for approximately 180 days to grow a pound given these conditions.
– this group was laid out like an orchard (12 ft centers) to keep one plant from shading another.
– this group took considerable work involving ladders
– the pot and surface soil were exposed to the sun
– half of the plant was always in the shade
– most of the plant matter(biomass) appeared to be infrastructure or support. Only 30% of the biomass was actual produce.
– the maintenance and tying was a lot of work – often involving cages
– it consumed the most water from mid July to mid September – right when the aquifer is low.
– it was harvested over two weeks in three stages.
– there were three distinct levels of quality: A (top buds), B (next tier, medium buds), and C (popcorn buds.)
– drying and curing were difficult in October during the rainy season. There were losses to mold.
– the crop was harvested when competition for sales is at its worst and prices are at their lowest. It did not sell until spring. It had to be stored for the winter. There was no money to pay the bills. There was no money to pay the employees. There was no money for Christmas.
– used 315 per bed (unit)
– yielded 2.0 pounds
– it took 158 gallons of water to grow one pound
– it used 3.5 gallons a day per bed (unit)……..almost a gallon a day less!
– it took 1.75 gallons a day for approximately 90 days to grow one pound.
– the beds did not shade each other
– all the work was at counter height. No overhead work. No work on ladders.
– the plants shaded their own soil
– the shallow soil seemed easier for the plants to utilize
– no part of the plant was in the shade
– most of the plant matter(biomass) appeared to be product not infrastructure. 70% of the biomass was product.
– once the initial netting was installed for the tie down there was no tying or support maintenance.
– it was harvest by early July so it never impacted the aquifer during the “red” months
– it was harvested in one day and in one stage (top bud only)
– there was one distinct level of quality: AAA top buds (control group never achieved this level of quality)
– this crop was harvested in July. It took no energy to dry it passively and there was no loss to mold.
– this crop was harvested early enough to sell at the peak high price for the season. The entire crop sold by October 1st; all the bills were paid and everyone got Christmas bonuses.
– this crops carbon footprint was considerably lower than the full term crop.
Dividing the total number of gallons used for “one unit’s” life cycle by the total number of days in the life cycle gives us the number of gallons used per day (x). Dividing the number of gallons used a day by the number of pounds per unit gives us the number of gallons per day per pound.
Total number of gallons / total number of days = x
Control group = 787 gals / 180 = 4.375 gals/day used / 2.5 lbs = 1.75 gal / day /pound
787 gals / 2.5 lbs = 315 gals / pound
Test group = 315 gals / 90 = 3.5 gals/day used / 2 lbs = 1.75 gal / day / pound
315 gals / 2 lbs = 158 gals / pound
Some comments on the various coefficients considered are listed below:
– Soil volume/surface area ratio: a low soil volume to a high surface area ratio allows the plant to breath, better utilize the soil volume, distribute water more evenly.
– Soil density: soils that contain wetting agents distribute moisture evenly, always accept water after drying, and may be recycled indefinitely. Heavy soils retain water at the bottom of the bed or pot while drying out on top. Heavy soils do not re-accept water after drying. Heavy soils must be replaced annually.
– Type of containment: plastic lined beds contain 100% of the water. Uncontained beds “bleed” from over watering and osmosis.
– Seed starts vs clone starts: seed starts are hearty, have a deep root system, strong upper structure, and use much more water. Clone starts are weaker, have shallow root system, weak upper structure, and use much less water.
– Total area occupied by a “unit”: the stand up plants require a large area around them to stop them from shading each other. In this study the area was 144 sq. ft. per “unit”.
A great advantage to the stand up plant is it can be grown on uneven ground. The light deprivation greenhouse requires level ground. The dep. bed occupies 40 sq. ft. per “unit”. The dep bed garden requires 30% of the space required by the stand up plant garden.
– Water application and distribution: although automated systems are much more efficient and dependable, in this study, water was administered by hand and measured. This insured that no water was lost in the process.
– Equilibrium: a plant’s proportions significantly affect its metabolic rate. Tall, skinny plants metabolize inefficiently, while short, wide plants metabolize efficiently.
– Evapotranspiration ratio: larger plants evaporate and transpire more than smaller plants
– Plant hydraulics: energy expended in pumping action per vertical inch of plant mass. Stand up plants expend a lot of energy just supporting their upper structure.
– Production biomass vs. support biomass ratio: the stand up plants are about 30% viable product and about 70% support structure. The opposite is true for the dep plants, they are 70% viable product and 30% support structure.
– Harvest process: the stand up plants took 2 weeks to harvest. The crop was never ready all at once. The greenhouse light deprivation plants were already at the same time and took one day to harvest.
– Product quality: the stand up plants had levels of quality: A,B,C. The highest quality of the stand ups never compared to the AAA quality of the greenhouse light dep cannabis.
As plants get larger, the amount of water utilized for one pound becomes larger in order to sustain the additional biomass of the “support system”. The first pie chart below shows the ratio of energy expended by the control group (30% product/70% support). The second pie chart illustrates the test group results (70% product/30% support).
Product quality is directly related to this ratio. As the ratio of marketable product goes down in relation to biomass so does product quality.
We believe that, paradoxically, more plants equal less water use. A higher plant count fills the soil volume faster, and, with light deprivation techniques, we can yield the same or more per year and use significantly less water.
Cannabis does not have to impact the aquifer during the dry months. The traditional method is at peak water consumption from August to October – the driest months of the year. The greenhouse light deprivation method does not consume any water during these months.
Humboldt county can raise cannabis quality dramatically and cut water use in half by moving towards light deprivation greenhouse growing.
As biomass increases past the point of “equilibrium” (when the plant grows taller than it is wide) cannabis reverts to a more “hemp like” product, resulting in a significant decrease in quality. As biomass increases past the point of “equilibrium”, the percentage of water utilized for gain decreases significantly, while the percentage of water diverted to support biomass increases significantly. This “ volumetric equation for biomass” incentivizes the Humboldt grower to use less water!
Finally, our concern is that a gross overestimate of water consumption will unfairly restrict Humboldt farmers. Faulty assumptions about Humboldt water use will also result in regulations that create a reduction in production and, therefore, market penetration. We do not hear anyone trying to restrict almond growers, but almond groves consume far more water than cannabis gardens. Let us base water use regulations here in Humboldt on common sense – talk to the farmers!
– Humboldt Growers Association proposed 2010 ordinance
– California State’s research article: “Impacts of Surface Water Diversions for Marijuana Cultivation on Aquatic Habitat in Four Northwestern California Watersheds.”
– Cannabis Voice: “6th draft ordinance”