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Thoughts On Nutrient Management

As the controlled environment agriculture science consultant to the Blue Seal stores throughout New England and an independent science consultant to the high value/medicinal sector – I take plant science very seriously. Your success as a grower and business person may very well depend on it. I field dozens of questions weekly on the best procedures for producing healthy, high quality, clean plants with the lowest input cost. Without a doubt, the two areas that generate the most questions and exhibit the largest knowledge gap are nutrients and lighting. In this handout I will try to shed some light on the subject of nutrient management in high value/medicinal crop (and food and floriculture for that matter) production and some of the issues facing grow room managers. In a subsequent handout I will address lighting issues.

     I spend time most nights researching the latest findings from around the world in the field of nutrient management/delivery and crop production (food and medicinal). Bottom line? There is still a tremendous amount of research that needs to be done to more clearly define the specifics of high value/medicinal crop nutrient requirements. Despite that fact, consider this quote from Cannabis Business Times in a recent article:

Despite the serious implications that optimal (or sub-optimal) nutrition can have on cannabis crops, the lack of academic research to substantiate or refute commercial cultivators’ nutrient practices, as well as the number of nutrient options and combinations available today—just 2% of cultivators who participated in CBT’s research said they are “not knowledgeable” about the nutritional needs of their crops.

Most cultivators said they are either “very knowledgeable” (36%) or “knowledgeable” (44%). Eighteen percent said they are “somewhat knowledgeable.”

     One of my goals is to help people look at some of the complex and confusing science in the controlled environment agriculture field and begin to make sense of it in a way that will help them incorporate that science into their production practices. The plant biology/organic chemistry/nutrient delivery matrix is one of those complex and confusing subjects. On the other hand, better understanding and properly manipulating that matrix is essential to success. There is no way I can even begin to adequately cover this subject here. Indeed, there are many PhD dissertations yet to be done trying to do just that.  So let’s step back a bit and try to get a basic overview.

     Plant nutrition and nutrient delivery cannot be looked at as a standalone element. Nutrient delivery and ultimate uptake by a plant is strongly influenced and affected by a number of other factors. These factors include but are not limited to: light intensity, light spectral profile, air temperature, vapor pressure deficit, physical properties of the grow medium (aeration, water retention, porosity, cation exchange rate, buffering capability), biome profile of the grow medium, CO2 levels in the chamber, type of nutrients being delivered (“organic”, water soluble), pH of the water, frequency of watering and the between watering moisture content of the grow medium, temperature of the water and  EC level of the delivered nutrient solution. And a huge factor in nutrient delivery/uptake in today’s high value/medicinal industry is genetic variations in strains.

     In short, nutrient delivery – in order to be “optimal” – must be considered a part of the entire controlled environment continuum. A change in any one of the environmental factors listed above will impact and alter the action of the other factors. For you as a grower to achieve “optimal” results, all of the listed factors must themselves be in their optimal range. If one factor is sub optimal, the entire process of transpiration/photosynthesis can only proceed at the rate dictated by that sub optimal factor. This is the Law of Limiting Factors. The classic – weakest link!

     Lights at the right height, CO2 levels good, soil a bit too dry – you get reduced transpiration and photosynthesis resulting in reduced growth, lower plant cooling capability, potential heat stress, reduced nutrient uptake, and wasted money on nutrients. Lights good, CO2 good, grow medium moisture level good, feeding according to feeding schedule, but vapor pressure deficit too low – you get reduced transpiration and nutrient uptake. I could go on and on with variations to this theme. The take away is this – to reap the maximum benefits of any nutrient regime you must understand that it works in exquisite harmony with all the other environmental factors in your grow chamber – no matter how big or small that grow chamber is.

     Over fertilization! It’s a serious issue in today’s cultivation climate. Consider this quote from the Mandala Seeds (a decades old and highly respected Dutch company) website:


Over-fertilization is a very common phenomenon in cannabis gardens and the #1 bud killer. We see more damage to flowering and yield through overfeeding than through any other gardening error. One of the main reasons is that the recommended dosages on fertilizers are way too high for the normal uptake of plants. Also growers fail to judge what the true plant requirements are during the grow and can be overzealous in wanting to make their plants grow bigger or better. Most people have fallen prey to the marketing of the agrochemical industry and believe that they need a cupboard full of bottles to grow successfully. The problem is enhanced by the low quality of cannabis genetics on the commercial market as many strains are too weak to grow vigorously by themselves and conditioned to respond to artificial feeding.

     Almost daily I am approached by growers seeing problems with their plants and making the automatic assumption that they either need to fertilize at a higher rate or get a new brand of nutrients. Rarely is either of these assumptions true.

     So how do you as a grower proceed? Let’s establish a few basic rules.

One: Become better educated about the workings of a grow chamber. Understand that you/we are trying to duplicate nature – indoors. Sounds easy but it isn’t! Do some studying of what it is we/you are trying to do in a grow chamber and how all the individual elements work together. How these elements are linked and how changing one element affects all the other elements. Know what the optimal environmental set points are for the plants you are growing and how to balance them.

Two: Understand that a LOT is still not/poorly understood and that whenever any company says that they have “the” product that everyone has been waiting for – step back and take a deep breath. Then explore the science from that company and compare it to the peer reviewed research data before you run out and buy that new miracle product. Plant nutrition has been being studied for many decades (indeed hundreds of years) by some of the top scientists in the world. It is not impossible but the odds are very low that two dudes in their garage in Humboldt are going to find the answer that PhDs in plant biology have been researching for decades.

     Also, the “coolness” of a bottle label or the quality of the graphics on that label has no direct correlation to the quality or performance of a nutrient product. And speaking of labels – read them! Very often you will discover that products with grand claims on their labels or in their advertising and a corresponding high price tag are actually no different than simply packaged, lower priced nutrients. A good example is liquid nutrient products. Many well-known national brand name lines are simply water soluble ingredients mixed with water, dressed with a fancy label and shipped across the country. You/we pay for that water, those fancy labels and those shipping costs. This is one reason many commercial grow operations buy water soluble nutrients in bulk and mix them themselves.

Three: Third party anecdotal information by itself is neither a valid nor reliable foundation upon which to build your plants’ nutrition program. Four or five years ago you may very well have had to rely upon the “advice” and “opinion” of other growers as you developed a nutrient application program. Not today. There has been a substantial amount of legitimate peer reviewed scientific research done looking at the nutrient needs of high value/medicinal plants. There is still much research to be done, but the data gathered already allows serious growers to precisely target their nutrient application protocols allowing them to more closely approach that optimal growth goal. If you are not currently approaching your nutrient application program from the standpoint of science/research data, then you are most likely falling further and further behind your competitors in yield quantity, quality and return on investment.

Four: Talk with the science-oriented person at your local professional grow center. They should be able to help you decide which nutrient program might work best for you. They should be able to discuss the intricacies of your particular grow environment and assist you in tailoring a nutrient regimen to help you maximize results while minimizing input costs. If the store employee can’t discuss the inter relationship of the various environmental set points and how they directly impact the plant’s nutrient needs and usage in your grow environment – ask to talk with their science resource.

Five: Understand one thing – there is no “one best fertilizer”. There are dozens (perhaps hundreds) of nutrient brands. If there were one “best” nutrient, why would Blue Seal or any other supplier carry anything but that one nutrient?  A key fact to consider is that different plant species – and indeed different varieties within each species – have different nutritional requirements for optimal growth. A fertilizer that is “perfect” for one plant type might be far from optimal for another type of plant.  Also, for example a fertilizer that performs very well in soilless grow medium might cause calcium and/or magnesium deficiency in the same plant grown in Coco coir due to very different cation exchange capacities. A fertilizer that performs very well in a high alkalinity potential water may cause problems when used in low alkalinity water. I could keep giving examples.

     A manufacturer can develop a “basic, all around” fertilizer that performs pretty well for many plants in the “average” conditions that home growers generally provide for their plants. Or, they can develop a comprehensive line of fertilizers that are targeted to meet the multitude of conditions that serious/commercial growers regularly encounter. Optimal growth depends on optimal nutrition. Optimal nutrition depends on a fertilizer specifically formulated for the plant variety, water chemistry and type of grow medium you use. Nutrients being delivered by any high-quality fertilizer are remarkably similar – well known and researched ions and ionic compounds. Method of delivery can vary – powdered or liquid formulation, one part or two part (or three part or four part or…), water soluble or “organic”. And indeed, these differences depend a lot on your personal preferences, particular grow space, budget and your personal “geek” factor rating.

     Remember this – whatever fertilizer you choose needs to be COMPREHENSIVE and BALANCED. Comprehensive means that it must contain all the macro, secondary and micro nutrients necessary for optimal growth of the plants you are growing. Balanced means that all the nutrients contained must be in the proper ratios to one another. This is a critical and all too often overlooked concept. Nutrients that are not in the proper ratios to each other can actually become antagonistic to each other. An example – too much nitrogen may cause a deficiency of potassium (K) and calcium (Ca). This is a key reason why mixing your own nutrient blends can cause a lot of problems if not done following strict scientific guidelines. You/we pay reputable manufacturers to know the science and create fertilizer formulations that are both comprehensive and in the proper ratios for our desired crops.  A note here – if you choose a particular nutrient system it is generally advised that you use that system singularly and use it in the manner it was intended to be used. Once you start adding products from other systems, your nutrient system can soon turn negative if you don’t use science and data to guide you.

Six: Don’t spend much time on the internet Googling “How to grow high value/medicinal crops”. The amount of false, incomplete, misleading, unsubstantiated, confusing information out there is scary. If you are not reading a peer reviewed research paper or data supported industry White Paper, you are probably reading science fiction and not true science.

Seven: True or False – if two is good, four must be twice as good! If you are unsure of how to answer this as it relates to nutrients and plant biology – I suggest that you go back to step one.

Eight: “Organic” verses water soluble? This is a very complex but important question. Both systems have their positives and negatives. Water soluble has the benefits of potential lower overall cost (especially when bought in bulk, dry format), speed of nutrient delivery to the plant, faster production time and capability of being delivered to the plants in a very precise and controlled manner. Compatibility with sensor monitoring and automation (precision fertigation) is high. This is why water-soluble nutrients are used by most commercial grow operations. Organic systems may produce stronger, “healthier”, more resilient, more pest and disease resistant plants with a “smoother” (a notoriously subjective term) tasting product. But production time can be longer, precision nutrient delivery is more difficult and complex, diagnostic tests such as pour through EC testing of the grow medium becomes less precise and the necessity of the grower having more acute visual diagnostic skills/experience becomes more important.  Over the past several years, there have been many peer reviewed research papers published studying the potential benefits of complex organic compounds (organic nutrient systems) on plants ranging from fruit trees to ornamentals, to tomatoes to high value/medicinal. The results? Organic nutrients with their complex organic compounds such as humic acid, fulvic acid, plant growth regulators, growth stimulants and many others can have positive impacts on plant growth, health, resistance, productivity, sugar content, taste, smell and yield. The reasons are many and complex such as higher NUE (nitrogen use efficiency), WUE (water use efficiency), lower carbon cost rates, positive enhancement of the symbiotic grow medium biome, positive impacts on chemical pathways such as the critical shikimate pathway, stabilization of grow medium pH, chelation of mineral salts etc. etc. No need to get too deep into the weeds here. The bottom line is that the benefits of organic nutrients/complex compounds are being more and more researched as a potential important element in the production of high quality, high yield plants ranging from fruits and vegetables to high value/medicinals.

     But – and this is an important but – just because a nutrient is “organic” does not mean that it’s use will therefore result in an automatically “better” end product. For example, a recent peer reviewed research study showed that the use of humic acid did show positive benefits to plant growth. BUT as the rate of application increased, there were marked shifts in the distribution of various chemical compounds in the plant that would greatly affect the potential dollar value of the crop. And that affect could be positive or negative depending on which market you were targeting – recreational or medicinal. Once again, this highlights the essential nature of science and data in crop production and business success.

      As a science consultant, I have spent a good deal of time over the past couple of years looking at the current trend of incorporating the best of both worlds – the speed and precision of water-soluble nutrients used in conjunction/collaboration with organic nutrient sources and bio-stimulants. Those using such hybrid application protocols are reporting very positive results including overall cost savings that can be quite substantial. I would suggest that you discuss such systems with your science based supplier.

Nine: Feeding schedules are a starting point not an end point. Most feeding schedules assume you are growing in RO or distilled water with an EC level of theoretical zero. We know that is not usually the case. Have your water tested for EC, alkalinity potential, pH, and major salt levels. Then choose and apply your nutrients accordingly. Most feeding schedules assume your grow room is perfectly tuned. Rarely the case – which will dramatically impact the nutrient needs, uptake rate, respiration rate, photosynthesis rate etc. of your plants. That in turn dramatically impacts the frequency, EC level and formulation of your nutrient regimen. There has been quite a bit of research done and reported over the past year looking at the relationship between individual nutrient elements (such as nitrogen, phosphorus, potassium etc.) and dry mass production, yield weights and yield quality. We have research data on EC levels that correlate to optimal production and quality figures. Data that correlates nutrient levels and productivity to various types of grow medium. And data that correlates nutrient levels and productivity to high and low light conditions. This is science. The data is there. The world is not flat. One such study to get a feel for what is going on in this field of research is:

Optimal Rate of Organic Fertilizer during the Vegetative-stage for Cannabis Grown in Two Coir-based Substrates,

by Deron Caplan, Mike Dixon, and Youbin ZhengSchool of Environmental Sciences, University of Guelph, Guelph, ON N1G 2W1, Canada. Available at:

Ten: Data track, data track, data track! The only way you know what is actually going on in your grow chamber is by collecting and analyzing data. Daily tracking (nighttime too) of major set point levels – temperature, CO2 levels, EC of nutrient solutions, relative humidity, etc. – is minimum. Once a week (at minimum) check grow medium EC levels with one of the pour through methods. Operating a grow chamber without data is like driving a car with your eyes closed. Both will most likely result in a crash!

     Remember, the fertilizer you choose to use and how you apply it is one part of a complex system that you/we employ to achieve optimal plant growth. To be truly successful you must understand the complex interrelation of all the environmental and physical elements in the grow chamber and better understand how to control and balance them. A great nutrient/fertilizer will not fully compensate for a poorly controlled grow chamber.

      I have thrown quite a bit of science at you here. I know that. But the high value/medicinal sector is  money intensive, competitive and science/tech driven and the HOLY GRAIL is the highest quality product at the highest yield rate at the lowest per unit production cost. Using science will help you get ever closer to that goal. The sector is getting more crowded every day and the stakes are getting higher (no pun intended). Those businesses that embrace science and use it to their advantage will have a much better chance of surviving and thriving. Those that don’t – well, most likely won’t.

Prepared by: David O’Connor – Controlled Environment Agriculture science consultant to Blue Seal