Micronutrients Part 2: Heavy Metal is Back!
Hi Guys, Dr. NPK here. I warned you that I was going to have my pun game on point. Anyway, time to finish up our conversation about the micronutrients: specifically, what each element does, and what signs indicate that there is a deficiency in the aforementioned element. (Check out Part 1 here) As a quick refresher, here is the list of micronutrients used in cannabis hydroponics:
Some say iron as well. I classify it as a secondary nutrient, separate post on iron coming up soon.
Manganese (Mn) – Mang, What an Important Element!
Real quickly, just want to make sure you understand, Manganese (Mn) is different than Magnesium (Mg). Despite being different, both manganese (a micronutrient) and magnesium (a secondary nutrient) are both involved in photosynthesis. Magnesium is incorporated into the chlorophyll molecule, whereas manganese helps with the photosynthetic process. Manganese is essential in starch development (aka carbohydrate); in chemistry, Manganese is an excellent oxidizer/reducer, so it can move electrons around efficiently. The ability to move electrons around helps it in the electron transport chain in the plant. (Mousavi et al. Aust. J. Basic & Appl. Sci. 2011, 5, 1799–1803). Manganese is also an important part in the activation of a variety of enzymes. The right amount of manganese means higher yields because photosynthesis efficiency improves.
Symptoms of manganese deficiencies are like magnesium deficiencies, because it affects the photosynthetic process, primarily yellowing the leaves (interveinal chlorosis). Manganese is less mobile than magnesium, so young leaves are affected more than older ones. One major reason that your plants may be short on manganese may be due to higher pH (Basic water interferes with manganese uptake), or the presence of a significant amount of organic matter (which outcompetes the manganese molecules in uptake). Remember to use chelated manganese products!
Copper (Cu) – C-u-Later Disease
I like copper the most of the micronutrients. My main reason for liking this micro so much is due to its benefits. Copper is a vital micro for setting up your plants for great lateral growth, as well as excellent disease resistance (notice how many fungicides contain copper?). Lignin biosynthesis needs appropriate levels of copper; lignin is a special macropolymer (say that ten times fast) that is used to support cell wall strength (Alaru et al. Field Crops Research 2011, 124, 332–339). Copper is also important in other enzymatic processes (it is a great electron transport agent, like manganese), but I really think the take-home message here is that copper means enhanced lateral growth.
Symptoms of copper deficiency are difficult to diagnose, as they are not quite as clear as other micronutrient deficiencies, but leaf wilting and stunted growth are good signs that you’re short on copper. Be careful! Copper toxicity is a real thing, so don’t go crazy and overcorrect with copper. Check to make sure your copper source is a chelated copper. I haven’t had much success with copper sulfate, it tends to get tied up by other ions in solution.
Molybdenum – WTF? Elite Base Nutrient A lists it as 0.0008%?! Is that Even a Number?!
Yes, ‘tis true, 0.0008% is a calculated number. Molybdenum is a nasty heavy metal that can affect human health in high concentrations. Most plant-friendly molybdenum sources are supplied as the “molybdate” (IE “sodium molybdate”). The molybdate form of molybdenum is just negatively charged (think of like magnesium sulfate, where the magnesium is positively charged and the sulfate is negatively charged — time to bust out your chemistry textbooks!). Molybdenum is a funny micro because it is more of a “support element.” Molybdenum is a vital element in the formation of the enzymes nitrate reductase and sulfite oxidase (Kaiser et al. Annals of Botany 2005, 96, 745–754). The key one here is “nitrate reductase” – molybdenum is required to support nitrogen processing in your plant. Appropriate molybdenum means nitrogen absorption which means green plants and growth!
Molybdenum deficiencies are very rare (a little goes a long way!), but the main reason is due to nutrient lockout resulting from low pH. The easiest way to tell if you have a molybdenum problem is if your plant is exhibiting what seems like nitrogen deficiencies but you’re sure your plants are getting enough nitrogen. Without molybdenum, that nitrogen can’t be processed.
Boron – The world’s greatest element ever.
Boron has a special place in my heart: my Ph.D. dissertation was centered around this element. Boron is extremely important in plant nutrition, and is one of the most common micronutrient deficiencies in crop nutrition today (Shorrocks, V. M. Plant and Soil 1997, 193, 121–148).
Thankfully, boron deficiency is rare in cannabis growing. Boron is one of the few micros that is not supplied in a chelated form. One of boron’s most important roles is in sugar translocation: it’s all great that photosynthesis creates energy and sugar, but just like any manufacturing location, product must be moved off the floor! Boron is one of the elements that helps facilitate this (Mitchell et al. Science 1960, 132, 898–899). Boron means more efficient photosynthesis, which means better yields!
Boron deficiencies tend to coincide with the symptoms of other macro deficiencies; leaf spotting and weak stems (boron is associated to the cell wall). Foliar sprays of boron are one option, but make sure you have the proper pH and ensure the nutes you are working with contain boron.
Side note: I know that some people use borax (sodium borate), but I would encourage you not to use this material because sodium is detrimental to cannabis in high quantities.
Cobalt – Not Just Your Favorite Type of Wedding Ring
Cobalt is up there with molybdenum in terms of being small players in the micronutrient realm. Despite being needed in small quantities, cobalt plays an important role in stem growth and elongation (Grover et al. Plant. Physiol. 1976, 57, 886–889). Cobalt is also an important support nutrient for nitrogen and potassium uptake. Cobalt therefore means better stem elongation and better yields!
Cobalt deficiencies, as previously mentioned, are rare, especially because cobalt doesn’t need to be chelated, so it’s hard to lock it out. Symptoms of this rare deficiency have to do with stem elongation and growth – if you are experiencing improper spacing and growth, cobalt may be the culprit. However, I’d check macros and secondaries first before pointing the finger at cobalt.
We have arrived at our last micronutrient, zinc! Zinc is an important micronutrient from a growth perspective. In small quantities it’s needed to ensure appropriate growth and prevent chlorosis. Like many of the other micronutrients, zinc should be in a chelated form (Zn EDTA for example). Zinc means improved yield and healthy intermodal spacing.
Being an immobile element, zinc deficiencies tend to manifest in the newer/younger leaves. These leaves will not only exhibit chlorosis, but also will be wilted and look generally unhealthy. Zinc, like cobalt and molybdenum, is required in small amounts. Zinc toxicity is a real possibility!
Dude, that was a lot of elements to discuss. The take-home message here is this: keep your pH at an appropriate level, and buy a micronutrient product that can really supply all the micros that you need. Elite Base Nutrient A and B provide all the micros that you need to help avoid the micronutrient deficiencies listed. Consolidation is always a nice thing!
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About the Author
Dr. NPK has been in the chemical formulating business for over 9 years. With a Bachelors in chemistry from UCLA and a Ph.D. in chemistry from UC Irvine, he has always had a passion for chemical formulation. Over the past several years, his focus has narrowed towards the research and development of products that are optimized for cannabis. He assisted in the development of the Elite Nutrient line and takes great pride in the products he created and uses himself. He has made it his mission to cut through all the pseudoscience available on the web and to educate readers on the science behind growing top-shelf bud.