Indoor cannabis production is a highly specialized and intensive form of agriculture. Unlike outdoor field or row crop agriculture, which bases productivity on acres, productivity in greenhouses is calculated on a per square foot basis. But unlike greenhouses, which make use of natural sunlight, the overwhelming majority of indoor cannabis gardens are lit entirely by artificial lighting. This puts indoor cannabis gardens in a class of their own.
Light, Space and Indoor Productivity
Outdoor and greenhouse growers base their productivity on yield per unit of area without much concern over the lighting the area receives. The thinking being that the intensity offered from natural sunlight is equal from grower to grower, and that open fields and sunny locations are sought out and selected by those growers to ensure that. The only changes in lighting they need to contend with are those doled out by Mother Nature, something they have no control over. Indoor cannabis gardens are not so fortunate. Indoor light intensity is not equal from grower to grower, and because indoor production depends so strongly on light intensity, the degree to which the average square foot of indoor growing space is productive will vary considerably depending on the type and intensity of artificial lighting chosen by each grower.
For indoor cannabis growers to enjoy the same benefits as conventional outdoor or greenhouse growers, whereby they can discuss and project yields on equal grounds based on past performance, they must account for not only space in their productivity language and calculations but artificial lighting as well. The YOR accounts for these variables by using square feet of canopy space and the average lumens available to that space in its productivity histories and projections. The inseparable interplay between space and available light is crucial to indoor growers, both will ultimately determine the production.
In the same way outdoor and greenhouse growers carefully select a location for their operation, indoor growers carefully select a canopy space within their location (closet, basement, spare bedroom, etc) on which they'll focus their light. The lamp too must be carefully chosen if a target production from that space is to be met.
Targeting Production - Finding and Synchronizing Production with Consumption
One goal of personal-use indoor growers is to divorce themselves from the black market. To be completely self-sustaining a grower needs to produce enough in one harvest to last him to the next. The alternatives - doing without or revisiting the black market - are not acceptable to most. To avoid that a grower must size his indoor garden to at least meet his own personal production needs. Most growers can estimate their needs by finding their weekly cannabis consumption and multiplying it by the number of weeks it takes to grow one full crop. This synchronizes the supply (production) with the demand (consumption).
Vegetative & Turnaround Times
The duration of a full crop depends largely on the maturity (flowering) time of the cannabis strain being grown, and to a lesser extent on the preparatory (vegetative) time preceding it. And though there are growing techniques for shortening or eliminating vegetative time, adding about three weeks of vegetative time to the strain's maturity time is usually a good estimate for the number of weeks it takes to grow one full crop (also known as crop cycle time or turnaround time). Generally speaking, crop turnaround time is about 12 weeks, thus a grower can produce about four crops per year, and each crop would ideally produce what the grower consumes during that 12 weeks.
Once consumption for the crop turnaround time is known, a crop production target can be established. Experienced growers see production rise and fall from crop to crop even though their garden is in a controlled indoor environment, as the hills and valleys in the graphic at the top of this page indicate. To make up for dips in production, a surplus of about 15% is added to the target as a rainy day safety margin. Some growers like to grow twice as much as they consume, or more, as a safety margin and as a way of planning an extended vacation between crops. Consider your own preferences, then adjust your production target accordingly.
Now that the production target in grams or ounces is known, a decision is made as to how much space and light are needed to meet that target. Space, light, and yield are so integrally tied to one another that you can't change one without affecting the others (see the Lighting Resources for more on space and light). In a perfect world you'd have more light and more space than you could ever want. In the real world, however, indoor real estate is at a premium, and security and cost concerns can nag at a grower to keep space and energy consumption down. This is where priorities are discovered.
One Priority - A Rock or a Hard Place
Is there more space available than could ever possibly be used, or is there limited space that might be too small to meet the production target? If space is limited, one can opt to give the space priority by using more light per square foot of canopy space. Space priority uses more light with less space, but produces the best yield for the available space. If space is unlimited, one can opt to give the light priority by using less light per square foot of canopy space. Light priority uses more space with less light, but produces the best yield for the available lamp.
Most growers want to get all the yield possible from both their lamp and their space. But as you'll see in the Production Table shown on the next page, the interplay occurring between space, lumens, and yield forces a grower to choose which is more important to him.
Because the construction of many grow spaces usually involves hammer meeting nail, the semi-permanent nature of the space can become a nightmare if a grower overestimated its production potential. Tearing down and rebuilding a grow space because it doesn't live up to expectations is something every grower wants to avoid, but most have probably done. Likewise, purchasing new lighting because old lighting proved inadequate is an extra expense that can be avoided with good planning.
Poor planning is usually the result of not having a realistic production target, or guessing at the space and light combination needed to meet it. Armed with a realistic self-sustaining yield target, the predictive resources shown below can help a new indoor grower take the guesswork out of planning, and thus avoid the dreaded re-work and second expenses that come back to haunt so many growers. However, if you don't know your target production, two of the yield calculators contain a self-sufficiency planner to assist you in that regard.
This table gives a general idea of the production to be expected from common HPS lamps when applied to different space and light intensity scenarios. Though not interactive, it does provide an overall graphic representation of the dynamics involved. For interactive resources, use the yield calculators shown below.
There are four yield calculator forms - HPS, MH, Advanced and Upgrader's. HPS and MH forms are dedicated to one lamp type, HPS or MH, and for single lamp gardens. All inputs are selected from dropdown lists. Because these forms are likely to be used by new growers or those unfamiliar with indoor cannabis cultivation scheduling, a self-sufficiency planner is included so that production and consumption can be synchronized with the maturity time for the strain being grown. A planner is not included in the advanced or upgrader's version.
The advanced version lets you enter data for multiple lamps and lamp types rather than selecting from a list of only HPS or MH lamps, but you will need to know their lumen ratings. You can also type in the light intensity instead of selecting it from a list, then fine tune it to fit a given canopy space. The range of light intensity is wider as well.
The calculator for upgraders is similar to the advanced version, but with some distinguishing features. It allows an experienced grower contemplating a garden upgrade to project yield for a proposed new scenario based on the relative success he's had from his old one. It uses two scenarios (before & after), and the grower's actual crop history (in grams) instead of the usual dropdown list for experience level.