California Cannabis Research Medical Group


O'Shaughnessy's Home

This Issue Home







Autumn 2004
Journal of the California Cannabis Research Medical Group

Understanding Plant Canopy Measurements

By Dianna Katherine Dearborn

This material is presented only as another way to explain the Medical Marijuana Garden Guidelines published by Safe Access Now (SAN) and Sonoma Alliance for Medical Marijuana (SAMM). The SAMM documents are the reference documents used here. The only exception is that MMPU no longer supports any numerical plant limits since they are arbitrary and counterproductive.

Plant canopy is defined as the area (on the ground) that a plant directly covers.

Plant canopy is defined as the area (on the ground) that a plant directly covers. Think of the measurement as the amount of ground covered by shadow if the plant were lit from directly above. The shape is roughly round.
As the plant grows taller, new foliage fills in at the bottom like ruffles on a skirt. The new leaves coming out on the bottom need ever longer stems to get to the sun. As soon as the new leaves get out from under leaves above and get sun, the stems don’t need to grow much more except to mature and fill out. Because the radius is larger at the bottom many more leaves can fit around the circumference of the plant than any comparable band above. In the table below, notice that the radius goes up evenly six-inches at a time but canopy area goes up rapidly as the plant matures.
To watch this happen as a plant grows, pick one leaf on one young plant and mark it with a ribbon or a wire twist tied loosely. That way you can focus on the same leaf every time you observe the plant. As new leaves grow in directly under the chosen leaf mark them also. See what you get when the plant matures.
The DEA, with pot to burn, grew and measured every part of the cannabis plant and process they could think of. The researchers found that one could predict the future amount of dried marijuana yielded by measuring the size of the growing plant’s canopy area.
DEA researchers found that every 100 square feet of plant canopy will yield 3 pounds of dried marijuana. This works for a few large plants or many small plants—regardless of THC content or bud maturity. Also, the canopy measure is scaleable, that is, 50 square feet of canopy will yield 1.5 pounds and 200 square feet will yield 6 pounds of dried marijuana.
Figuring your plant and garden canopy sizes involves some simple math, but don’t worry, with a cheap handheld calculator the process is as simple as following a recipe.
The very first thing you need to know is the radius of every plant in your garden to get an exact result for your calculations. The radius is the distance from the stem to the tip of a leaf at the bottom of the plant. you can simply measure one plant and multiply by the number of plants in your garden—if you planted all plants at the same time and they mature in the same environment. If the cops become interested in your garden, insist that the radius of every plant be measured and garden canopy calculated on the spot. Cops will probably measure the greatest radii of the “roughly round” canopies and patients will find the least radii.
Since we are dealing with a round canopy shape we will need to use the mathematical constant p (pronounced pi) which is simply the number 3.14, don’t worry why. The other math thing you will need to know how to do is to square a number. You simply multiply a number by itself. So, the formula for the area of a circle is, formally, A = pr2 which is read as “the Area of a circle is equal to pi time the radius squared. We can also write it as Canopy = the radius times the radius times 3.14, or...

Plant Radius Radius X radius Canopy = radius x radius x 3.14 Number/plants in 100 sq ft canopy
1/2 foot 0.25 0.8 square feet 126 very small plants
1 foot 1.0 3.1 sq feet 31
1.5 feet 2.25 7.0 sq feet 14
2 feet 4.0 12.6 sq feet 8
2.5 6.25 19.6 sq feet 5
3 feet 9.0 28.3 sq feet 3




O'Shaughnessy's is the journal of the CCRMG/SCC. Our primary goals are the same as the stated goals of any reputable scientific publication: to bring out findings that are accurate, duplicable, and useful to the community at large. But in order to do this, we have to pursue parallel goals such as removing the impediments to clinical research created by Prohibition, and educating our colleagues, co-workers and patients as we educate ourselves about the medical uses of cannabis.
The Society of Cannabis Clinicians (SCC) was formed in the Autumn of 2004 by the member physicians of CCRMG to aid in the promulgation of voluntary standards for clinicians engaged in the recommendation and approval of cannabis under California law (HSC §11362.5).

As the collaborative effort continues to move closer to issueing guidelines, this site serves as a public venue for airing and discussing these guidelines.

Visit the SCC Site for more information.