We dove into preparing this issue for press just as we returned from Cannabis Conference 2019 (produced by Cannabis Business Times and Cannabis Dispensary) in Las Vegas, Nev. While we launched the show three years ago, this was the first time we incorporated dispensary education and exhibitors into what was previously a cultivation-focused event. The landmark three-day conference united plant-touching businesses under one roof. The results were, for me, unforgettable.

Few opportunities exist where you can get together with not only your peers, but also your retail counterparts in this industry, and have the forum to learn together and have in-depth discussions about the challenges and opportunities you face. There was a definite spirit of collaboration throughout the entire event. Breeders and cultivation experts, scientists and extraction innovators, business owners and operations managers, university professors and researchers, dispensary owners and senior staff hailing from businesses of all scopes and sizes came together to share their passion for the cannabis plant, this industry and their roles in it.

"If you’re the smartest person in the room, you’re in the wrong room."

Thanks to your valued feedback and that of our advisory board and speakers, this year stood out to me as nearing the pinnacle of education for plant-touching businesses. There is a saying, “If you’re the smartest person in the room, you’re in the wrong room.” As I sat in sessions, visited the speaker lounge and walked the exhibit hall to chat with attendees and exhibitors, I knew I was definitely in the right room.

But there is always room for improvement, and the Cannabis Conference team is already working to make Cannabis Conference 2020 the best one yet. (Save the date: April 21-23, 2020, at Paris Las Vegas!) If you have suggestions you’d like to share, feel free to email me anytime.

Each year, new products and technologies come to market that can help commercial cannabis growers speed plant growth, improve yields and decrease production costs. Immediate changes to the grow environment, however, can place a crop at risk, and improperly introducing new products into your cultivation program can result in missed deadlines, damaged plants and even crop failure.

Improperly introducing new products into your cultivation program can result in missed deadlines, damaged plants and even crop failure.

New cultivation materials should be cautiously introduced into the grow environment, and preferably trialed on a small scale first. Not only does this make good grow sense, but it is a fundamental tenet of Good Manufacturing Practices (GMPs). GMP-compliant growers follow very strict guidelines when it comes to changing cultivation practices or introducing new materials into production.

The following guidelines can help ensure that your next cultivation purchase is a blessing to your operation, not a curse.

Fertilizer

Growers frequently experience plant issues as the result of introducing new fertilizers into their cultivation program. Most operations use fertilizer with each irrigation, and it’s applied to thousands of plants at once. If a new fertilizer is mixed incorrectly, or reacts poorly with the grower’s substrate, plant problems can manifest themselves in the form of burned leaves, discolored pistils or dead roots.

For hydroponic growers, switching out premixed hydro-shop nutrients for a different brand can be risky. Mineral ratios will differ between brands, and some plant additives are not required to be listed on the product label. For organic growers, new liquid fertilizers or compost teas can be risky as well because it can be difficult to guarantee the consistency of ingredients in these mixes. Compost teas that aren’t properly brewed can negatively affect plant health, and even properly prepared liquid organic fertilizers have a short shelf life.

The correct way to introduce a change to your fertilizer regime is by first trialing the new product on a small portion of your crop. For new hydroponic formulas, make sure to follow the label and test the final solution with an electrical conductivity (EC) pen. For new organic fertilizers, be aware of the product’s expiration date and discard the product if not used before then. In both cases, if the fertilizer is purchased in large volumes, it is a good idea to perform a solution analysis on each lot prior to use.

Eric Limon | Adobe Stock

Growing Media

Cultivators may want to change their growing media to decrease production costs, but a dramatic change in substrate composition can catch cultivation teams off guard. For example, when plants have fertility issues due to a growing media switch, growers must rethink their fertility and watering programs. The setback can cause slow plant growth and missed production deadlines.

When using coconut products (coir, fiber, etc.) the potassium, sodium and chloride content can vary drastically between brands. Some manufacturers/suppliers triple-wash and pH-buffer their products to remove salts and provide for better nutrient uptake, yet others skip this step, and growers must adjust their plant nutrition protocol to account for the higher salt content.

When plants have fertility issues due to a growing media switch, growers must rethink their fertility and watering programs.

Most organic growing media components are not composted, but if a composted material is being used, it needs to be properly “cooked” during the compost stage, meaning the microorganisms in the compost must be given time to break down the raw material (in a process that naturally creates heat as a byproduct); uncooked or poorly prepared compost can burn plant roots and shoots. Different raw materials affect nutrient availability in an organic mix, so growers will need to adjust their watering and fertility programs to find a proper balance.

A media analysis can help provide information like high salt content or unfavorable pH values at the outset, and the risks inherent to introducing new growing media can be mitigated by selecting a reputable supplier to work with that can formulate the proper media mix for your operation. Proper media formulations will guarantee optimal/desired physical properties (porosity, air, water, etc.) essential for crop management.

If feasible, it is also helpful to perform a small trial of one complete crop cycle prior to switching over the entire operation.

Lights

The temptation to upgrade to new lights is very compelling, and with good reason. Today’s horticultural grow lights provide more power, use less electricity, and some even enable growers to customize light spectrums to encourage cannabinoid production. However, if you don’t slowly introduce your plants to a new light source, you’re likely to encounter problems.

Whether you’re going from 600-watt high-pressure sodium (HPS) to 1,000-watt HPS), or HPS to light-emitting diode (LED), you need to trial these products before implementing them on a large scale. For indoor growers, moving from a lower-wattage HPS to a higher-wattage HPS could overwhelm the HVAC system and cause heat burn to the plants. On the flip side, some growers are so delighted with the low heat output of LEDs that they place the plants too close, and as a result experience crop bleaching—the plants could literally grow white buds.

If you are thinking of upgrading to stronger lights, make sure your HVAC system can handle the increase.

Even if the supplier swears you won’t have any problem incorporating its new lights into your grow, or you know of industry colleagues that have seamlessly made the transition, it is still your responsibility as the grower to minimize potential damage to the crop by testing these lights first. If you are thinking of upgrading to stronger lights, make sure your HVAC system can handle the increase. If possible, establish plants at a greater distance from the light than is recommended by the manufacturer, and slowly bring the lights closer over the next five to seven days. If light height is fixed, try dialing back light intensity, or use fewer lamps initially and slowly build up to full strength. If no negative effects are evident after one week, it should be safe to introduce the lights to the entire crop. Still, play it safe and slowly introduce your entire crop to your new light setup.

Advanced Hydroponics

Aeroponics and deep water culture (DWC) are advanced forms of hydroponics that use no substrate at all. Plant roots are either suspended in air and misted with nutrient solution, or they are bathed in constantly flowing oxygenated water. Switching to these cultivation methods can appeal to growers because the systems use less water, grow plants more quickly and avoid the risk of soil-borne diseases.

Although the advantages may be obvious, moving from substrate growing to aeroponics or DWC is a huge jump. These systems demand tight control over water temperature and dissolved oxygen levels, and there are a near infinite number of spray nozzles and tube junctions that could clog, leak or rupture. Equipment and systems need to run in perfect unison, and they can be especially risky for start-ups because they are more prone to unexpected interruptions in power supply.

The best growers establish their toolkits of new pest control products before they need to use them.

Growers interested in evolving their programs in this direction should consider setting up a research and development (R&D) station to trial these systems first. Get used to the increased vigilance of new equipment and all the intricacies of running these ultra-high-tech hydroponic systems. After a few mini-crop cycles, the grower can decide if this upgrade makes sense to incorporate over several thousand square feet of cultivation. (Editor’s note: For more information on these hydroponic systems, see the article “Are You Well Versed in Hydroponics? Part II” in the March 2019 issue of CBT.)

Pest Control Products

A common misconception is that organic pesticides and fungicides are not as effective as their chemical counterparts, and as such, the introduction of new organic products are safe in any amount. Unfortunately, many growers find out the hard way that this is simply not true. I have repeatedly witnessed plant damage that was the result of using all-natural pest remedies, such as neem oil. Although 100-percent organic, if neem oil is applied at a high rate, or to dry plants, or in the heat of the mid-day sun, plants are likely to suffer.

The best growers establish their toolkits of new pest control products before they need to use them. This is because most spray applications are done urgently, when pest or disease pressure is severe, and the grower doesn’t have time to perform plant compatibility tests. The only thing worse than having a severe insect outbreak on your crop is to further aggravate plant problems with the use of a non-compatible pesticide.

Trials only need to involve a few plants, but they should be representative of the entire crop. Plants should be in good health and recently irrigated, and the spray application should occur in the early morning or late afternoon in a greenhouse, or under reduced light if indoors. Application rates are stated in ranges on the product label, so start at the low end of that range. If after 72 hours no phytotoxicity is evident, the product should be safe to apply in the same manner to the rest of the crop. If phytotoxicity does occur, trial the same product again at half strength or replace it with different product and begin the trial again.

fona | Adobe Stock

For controlled-environment-grown crops, substrate pH and electrical conductivity (EC) are two main factors that can easily be monitored to make sure your crop is on track for success. This monitoring principle has been used by the commercial floriculture industry for the past 40 years, and it can be adopted by the cannabis (Cannabis sativa) industry, too. Monitoring and managing the substrate pH and EC could help to avoid up to 80 percent of the plant nutrition problems that occur with controlled environment crops. (For more on optimizing pH, see the first article in North Carolina State University's (NCSU) ‘Nutrient Matters’ series in the March 2019 issue of Cannabis Business Times.) In this column, we’ll discuss what EC is, why it’s so significant to crop health and how to measure it.

What is EC?

Electrical conductivity is the electrical charge that moves through a solution. The higher the salt concentration, the greater the electrical reading. This principle is applied to controlled environment production because the higher the concentration of fertilizer salts in the solution or in the substrate, the higher the EC reading will be. We can then monitor the EC level to ensure that fertility levels are where they need to be.

What EC Does (and Doesn’t) Measure

The EC is a measurement of the total amount of fertilizer salts in the solution. It does not provide specific information about each individual element or that individual element’s concentration in solution.

The good news is that with controlled environment production, the primary nutrients we provide are nitrogen (N), phosphorus (P) and potassium (K). Therefore, with most cases in both theory and practice, the EC reflects the relative concentration of those elements. You can apply this concept to cannabis to confirm the accuracy of the fertilizer concentration you apply in the solution and to monitor the crop’s nutritional status.

Lower-than-optimal EC readings typically indicate a nutrient deficiency, especially low levels of N (Fig. 1). High EC levels can indicate you are supplying too much fertilizer or that your plants are not absorbing the nutrients, both of which can lead to a salt toxicity leaf burn.

Doing the Math

If you are using a fertilizer such as 13-2-13 Cal-Mag, the label on the back of the bag provides EC guidelines to help you double-check the accuracy.

For example, if you want to provide 200 ppm of N to the crop from a 13-2-13 Cal-Mag solution, then you would need to mix 20.76 ounces in 100 gallons of water. (This is based on Jack’s brand fertilizer. Manufacturers use different salts to achieve a similar analysis, so you need to utilize recommendations on their labels to be correct.) Alternatively, if using an injector set at a 1:100 ratio, that would mean adding 20.76 ounces of Jack’s Cal-Mag into a gallon of water to make a concentrate that is then run through the injector. Either way, the corresponding EC of that final diluted fertilizer solution should be at 1.64 millisiemens per centimeter (mS/cm, the unit by which EC is measured), as listed on the product’s label.

By measuring the EC, you can double-check your mixing procedure and confirm if your fertilizer injector is working accurately.

Accounting for Irrigation Water EC

You must also take into account the EC contribution of your irrigation water. If your irrigation water has high concentrations of alkalinity (calcium (Ca), magnesium (Mg) or sodium (Na)) then when you test the EC of your fertilizer solution or substrate, your values will be artificially elevated, too. When monitoring the fertilizer solution you are supplying to the plants, knowing the EC contribution of your irrigation water is important. This requires that you periodically have your water quality tested by a commercial lab.

In Raleigh, N.C., we have very pure water, and normally the EC is around 0.11 mS/cm. Therefore, we must add the EC contribution of the irrigation water to the EC contribution of the fertilizer to determine the corrected target EC. This would mean the final fertilizer solution EC should be 1.75 mS/cm (1.64mS/cm fertilizer contribution + 0.11 mS/cm water contribution). In contrast, for much of the Midwest, the EC of the irrigation water is much higher. If the water EC was 1.13 mS/cm, the same final fertilizer solution EC would instead be 2.77 mS/cm (1.64 mS/cm fertilizer contribution + 1.13 mS/cm water contribution) to also provide 200 ppm N from a 13-2-13 Cal-Mag fertilizer by Jack’s.

cendeced | Adobe Stock

Accuracy Check

Your fertilizer solution EC value can be used to check for fertilizer delivery accuracy. If it is not within 5 percent, then you need to double-check the mixing math, the accuracy of measuring out the fertilizer salts, or if the injector is malfunctioning. The EC values will be significantly lower as the injector begins to fail, which in turn will slow growth for plants grown in soilless substrates and, under prolonged conditions, cause lower-leaf yellowing due to inadequate fertility.

Hydroponic/Rockwool System

If you are growing a cannabis crop hydroponically or in an inert substrate such as rockwool, you can monitor the fertilizer EC value to ensure you are providing the correct fertilizer concentration.

Measuring the Substrate EC

If you are utilizing a soilless substrate containing sphagnum peat moss or pine bark, you can use another aspect of EC monitoring to make sure your fertilization program is on track.

Begin an In-House Nutrient Monitoring Program

A wide assortment of pH and EC meters is available on the market. At NCSU, we recommend combination pH and EC meters. The majority of growers we work with purchase a unit that costs less than $200.

Monitoring and managing the substrate pH and EC could help to avoid up to 80 percent of the plant nutrition problems that occur with controlled environment crops.

After purchasing a combination pH and EC meter, you need to start using it! The majority of the commercial floriculture greenhouse industry relies upon the non-destructive PourThru monitoring method to test EC and pH. Weekly or biweekly sampling is the key to ensuring your EC and pH levels are on track. While cannabis-specific recommendations based on scientific research have not been published, sampling procedures (including the PourThru method) can be found at the nutrient monitoring website: fertdirtandsquirt.com and general EC guidelines are provided in Fig. 2 above.

Target Fertilization Rates and EC Levels for Stages of Plant Development

The nutrient demands of plants change over the course of development. Young transplants focus energy on establishing roots and add little leaf growth; as such, they require less fertilizer. As plants grow and bulk up, fertilizer needs increase. The number of leaf and flower nodes on each plant sets when the photoperiod changes and flower formation begins. This terminal inflorescence (flower production) establishes how much more growth will occur. At this stage, the amount of vegetative mass the plant adds is less, yet energy and resources are still required for flower/bud development. With this shift from vegetative growth to flower growth, the nutrient demand lessens. Given how a plant grows and adds mass, and how nutrient demands vary over time, it comes as no surprise that nutrient delivery needs to be customized to meet the changing demands of the crop throughout its different growth stages.

The EC is an indirect measure of the fertilizer salts contained in the substrate, so those target levels will also vary at different growth stages. By starting an in-house nutrient monitoring program and measuring the EC, you can make sure that sufficient levels of fertilizer are available to the plants. Recommended fertility levels and target EC levels based on the stage of cannabis plant development are listed in Fig. 2, as measured by the PourThru method.

Ammoniacal-Nitrogen, Urea and Organic Fertilizer Adjustments

Though measuring the EC is an excellent tool when utilizing water-soluble controlled environment fertilizers, there are limitations to this measurement. When it comes to measuring the contribution of N to the EC, nitrate-nitrogen (NO₃-N) can be measured; however, the other two common forms of nitrogen included in fertilizers—ammoniacal-nitrogen (NH₄-N) and urea—cannot be measured by EC. The EC charts on the fertilizer bag, or provided by the manufacturer, will reflect those lower target EC values. Likewise, most organic fertilizers rely upon ammoniacal-nitrogen (NH₄-N) and urea for their derived sources of N. Be aware of this fact when you are mixing the fertilizer solution. In addition, you must then adjust down the target EC ranges accordingly when testing the substrate EC.

glorcza | Adobe Stock

The Bottom Line

Optimizing fertility management is a strategy of supplying the appropriate level of nutrients to cannabis to meet the demands for plant growth. If the supply is too low, then the genetic potential of the plant is hindered because of the deficiency, and the plant will flower less. Elevated fertilizer levels can lead to excessive leaf and shoot development at the expense of flower growth. Excessively high levels of fertilizer in the substrate can also lead to stunted growth.

The good news is that conducting periodic PourThru sampling of both the EC and the pH will help you monitor the nutrient status of your crop to ensure it is on track.

Brian Whipker, Turner Smith and Paul Cockson are from Department of Horticultural Science, North Carolina State University, Raleigh, N.C. Hunter Landis is from North Carolina Dept. of Agriculture and Consumer Services, Raleigh, N.C.