Establishing a Well-Balanced Cannabis and Hemp Fertilizer Program

By Griffin Greenhouse Supplies|May 26, 2022

Cannabis and hemp are moderately heavy feeders, especially enjoying a relatively high calcium supply. A rigorous and well-balanced fertilizer program can be achieved with any number of fertilizer inputs, but the most successful are tailored to an individual operation’s needs.

A Griffin CEA Tips blog post highlights why the choice of fertilizer formulation should be made based on water quality, irrigation equipment and growing media, and type of production system.

First, evaluate water quality. Growers should understand the pH, EC, alkalinity, and general mineral salt content of their water source. Municipal water supplies may change in composition from season to season – these water supplies should be tested at least once or twice a year. Well-water may also change seasonally and should be tested initially to gain an understanding of the water quality, then monitored yearly for changes to ground water conditions. When using reverse osmosis (RO) water, regular service and monitoring should be performed to make sure the filtration system is functioning as expected. Water sample test kits can be ordered and sent to a variety of labs for very reasonable prices.

Second, take stock of your irrigation equipment and available labor. Are you hand watering or using a drip system? How much water are you using on a daily basis? Some fertilizer stock solutions can be stored on site for weeks without issue, while others must be consumed quickly, in a day or two. Next, what type of media are you growing in? Truly hydroponic systems require control of the EC and pH of fertilizer water using consistently performing products. The pH of peat-based or soil-based media is most affected by the alkalinity of the water. Low to moderate alkalinity often can be managed with the proper fertilizer choice.

Hemp and cannabis growers treat excess water alkalinity through the application of acid along with the fertilizer. Sulfuric acid is the number one choice for this crop. High-alkalinity water presents a special challenge to organic growers. The only Organic Materials Review Institute (OMRI)-approved acid is citric acid; high alkalinity requires large amounts of citric acid to neutralize the excess. Organic growers may consider purification systems when faced with poor water quality.