Autumn 2004
O'Shaughnessy's
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 sixinches 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 