How much usable marijuana is available from a single marijuana plant? Is it one pound, five pounds, 15 pounds or four ounces? One can likely make a case for any and all of these figures. It resembles the question, "How many tomatoes does a single tomato plant produce?" For tomatoes, like marijuana, the answer varies depending upon the variety, growing conditions, horticultural practices and harvesting techniques.
The usable quantity of marijuana is in part determined by the potency as measured by the amount of psychoactive agents within the finished product. Potency is effected by the moisture remaining after drying, what parts of the plant will be included as well as the variety, growing conditions, horticultural practices and harvest timing. While some plant varieties are grown specifically for their potency with the most psychoactive ingredient percentages topping out at more than 25 percent, most remain in the 10 to 20 percent range.
In addition to the advent of female-only clones, today's marijuana grower has an ever-increasing number of choices available to affect the outcome of the crop. The most dramatic difference between plants involves indoor versus outdoor growing habits. Given reasonable local growing conditions, outdoor plants will yield significantly more marijuana per single plant than indoor ones. Good growing conditions and well-suited cultivars for the area can grow enormous marijuana plants yielding 10 to 15 pounds of bud marijuana each, as shown in the large marijuana plant located by the County of Mendocino Marijuana Eradication Team several years ago. Mendocino County sheriff's deputies report seeing giant stands of this type more frequently in recent years as grows have moved more into the open to take advantage of full sun exposure as well as improved horticultural practices.
The U.S. Drug Enforcement Agency uses an average dried weight of one pound of usable marijuana leaf and bud per mature plant based on yield studies conducted across 15 states in the 1990s, which at that time included the typical presence of 50 percent male plants. In controlled grow studies in Mississippi, the DEA concluded female plants could readily yield five pounds of usable bud and leaf material. The DEA found providing more room for the growing plants increased the yield and plants receiving more water and nutrients were bigger. The DEA plants yielding five pounds of dried bud and leaf were about 8 feet high and 8 feet in diameter with 50 square feet of canopy each. The DEA concluded diameter was one of the best predictors of finished yield.
In 2004, Humboldt County adopted a medical marijuana ordinance establishing a maximum mature female marijuana plant canopy standard of 100 square feet rather than a plant limit. The ordinance determined 100 square feet of marijuana plantings would typically "yield three pounds of dried and processed cannabis bud per year." The county set the three-pound limit as "a reasonable amount for medical marijuana patients to cultivate, possess and consume."
When assessing yields from indoor grows, horticultural practices vary so much it is difficult to determine an average yield per plant. While plants in typical indoor grows seldom exceed four foot in height, a Laytonville indoor grow in September 2007 had 104 plants each between 10 and 15 feet tall when raided.
Most in the industry use area rather than plant numbers for determining indoor grow yields with grows primarily limited by the amount of light available to the plants. Since little light penetrates more than a few feet into the plant, there are few benefits associated with growing tall indoor plants. This leads many growers to opt for bunches of smaller plants. For indoor plant yield, horticultural practices including the number of crops per year coupled with plant selection are the major factor.
The district attorney in Humboldt County issued separate guidelines for medical marijuana indoor grows maintaining the 100 square foot maximum canopy limit established for outdoor grows but adding a maximum 99 plant limit (including starts) and a maximum light source of 1.5 kilowatts.
Most indoor growers strive to get the maximum marijuana yield possible from the high costs of generated or purchased electricity used for the grow cycle. The more sophisticated grower can also reduce the cycle time between crops with hydroponic techniques and improve yields with light spacing and selection, managing disease, optimizing water and nutrient uptake, carbon dioxide augmentation, dehumidification and plant selection.
While there is no particular standard for the number of plants each light can support, most agree about 40 watts per square foot is desirable for rapid plant growth. Several grow sources suggest a reasonable target for an intermediate grower of one pound of bud for each kilowatt of lighting used per grow cycle. Four annual grow cycles are typical with as many as six cycles achievable with hydroponics, excellent light management and good plant selection. At the local cost for electricity of about $.16 per kilowatt, the monthly electricity cost to power a one-kilowatt lamp is about $80 (based on 16 hour per day light usage).
Current medical marijuana limits
California wide limit: Possession of half pound of dried marijuana, six mature plants or 12 immature plants. Most counties use this limit. These limits apply in 49 of the 58 California counties.
Current Mendocino County limit: two pounds of dried marijuana and 25 adult female plants.
Humboldt, Sonoma and Santa Cruz counties permit three pounds of dried marijuana and 100 square feet of growing plants. Del Norte County allows one pound of dried pot with 99 plants and 100 square foot limit. Butte County enforces the California plant limit but increases possession to one pound and Calaveras County to two pounds. Trinity County has a three-pound limit with 12 mature and 24 immature plants. San Francisco limits individual medical users to 24 plants in 25 square feet and a half pound of dried marijuana for dispensary gardens the limit increases to 99 plants and 100 square feet.
Cutline: Sheriff's Lt. Ron Welch standing next to a large marijuana specimen.
COMMET crew walking through a pot forest.
