The desire to strike it rich has given rise to traditional farms tearing out crops in favor of the promising cash crop cannabis. ELI WEISSMAN does the math behind the essential light science that yields good crops.Feb 25th, 2020
Marijuana greenhouses are an ideal business to capitalize on the “greenrush.” Most commonly referred to as cannabis by industry professionals, this cultivar is possibly more valuable than any greenhouse crop in the history of agriculture. Cannabis is worth 100 times more per unit area than other high-value greenhouse crops. As LumiGrow CEO Jay Albere presented at the 2019 HortiCann Light + Tech conference, making comparisons to cucumbers, peppers, and tomatoes, each of those crops is valued at less than $100 gross revenue per square meter per year, whereas cannabis is valued at $12,900 gross revenue.
However, to achieve such financial heights, a grow operation must be built upon proper understanding of the supplemental lighting needs in the greenhouse environment (Fig. 1). In this article, we’ll walk through a real-world cannabis greenhouse scenario and show how a greenhouse in a high-light region can still gain an additional $13.7M (million) per acre per year in revenue.
How does light impact yields?
The greenhouse method is generally preferred because, let’s face it, sunlight is free. As mentioned, cannabis is a demanding crop with high light needs. Growers can’t afford to lose on yields, but it is also important to know how much yield will be gained by adding supplemental light. Let’s look at how far more light will go in a cannabis greenhouse.
The cost to light an acre of greenhouse space at an average supplemental intensity (or PPFD — photosynthetic photon flux density) of 400 μmol·m-2·s-1 is a little under $1M. This may seem like a high cost, yet each additional light fixture a grower provides is like a revenue engine — which can pay itself off in just the first year by increasing flower yields.
At optimal light levels, greenhouse cannabis flower is worth approximately $39M annually per acre. It’s important to note that any light quantity below a daily light integral (DLI) of 40 mol·m-2·d-1 reduces this value. The DLI is a measure of photosynthetically active radiation (PAR) received each day as a function of light intensity and duration.
Horticulturalists generally follow a 1% rule: For most crops, 1% more light means 1% more yield. Cannabis too typically follows this classic rule of thumb; however, there is a point of saturation where the rate of increasing yield diminishes.
FIG. 2. Cannabis flower weight increase (g/plant) is correlated to increases in light intensity, but tends to stabilize between 35 and 52 mol·m-2·d-1. This data can help growers determine how best to utilize supplemental lighting. (Data used with permission from Allison Justice Study; OutCo, The Hemp Mine.)Dr. Allison Justice, a plant scientist and founder of The Hemp Mine, has demonstrated that the amount of trimmed cannabis flower that was harvested increased by 1% for every 1.1% light intensity increase between a DLI of 17 and 25 mol·m-2·d-1 (at 1500 PPM CO2). As shown in Fig. 2, the rate of yield gain slows between 35 and 52 mol·m-2·d-1. Between these light levels, trimmed flower weight only increases by 1% for every 5.5% increase in light quantity. (Justice’s work has been quoted and represented with permission.)
Lighting at 52 mol·m-2·d-1, as Justice did, ensures that yields will stay stable long into the future. This is due to the light loss effect, also known as lumen depreciation, or most recently in horticulture as the yield loss factor.
So for growers with greater capital and a long-term business plan, providing 52 mol·m-2·d-1 can make financial sense. For growers that are just getting started, 40 mol·m-2·d-1 will provide adequate return on their investment.
Cannabis case study
Now that we understand just how much optimizing light quantity will increase yields, let’s compare the supplemental light needs in Arizona; Vancouver, Can…….
