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 (I classify it as a secondary, separate post on iron)

Manganese (Mn) – Man, What an Important Element!

Real quick, just want to make sure you understand: Manganese (Mn) is different than Magnesium (Mg). Despite being different, both manganese (a micro) and magnesium (a secondary) are both involved in photosynthesis. Magnesium is incorporated into the chlorophyll molecule, whereas manganese helps with the photosynthetic process. Manganese is essential in starch (aka carbohydrate) development; in chemistry, Manganese is an excellent oxidant/reductant, so it can move electrons around efficiently. This ability to move electrons around helps it in the electron transport mechanism 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. Right amount of manganese = higher yields (because photosynthesis is being efficient) + excellent carb production.

Symptoms of manganese deficiencies are like magnesium (because it affects the photosynthetic process): yellowing of leaves (interveinal chlorosis). Manganese is less mobile than magnesium, so young leaves are affected. One major reason that your plants may be short on manganese may be due to higher pH (the basicity of the water interferes with the manganese/prevents appropriate uptake in the root zone), or the presence of a significant amount of organic matter (again, outcompetes the manganese molecules). 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 copper = enhanced lateral growth.

Symptoms of copper deficiency are difficult to diagnose (it’s not quite as clear as other micro deficiencies), but leaf wilting + stunted growth are good signs 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 gets 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” – such as “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…bust out the 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 for me is “nitrate reductase” – molybdenum is required to support nitrogen processing in your plant. Molybdenum = nitrogen absorption = green plants and growth!

Molybdenum deficiencies are very rare (little goes a long way!), but the main reason is due to nutrient lockout due to 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, it 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 = more efficient photosynthesis = better yields!

Boron deficiencies coincide with other macro deficiencies; leaf spotting and weak stems (boron is associated to the cell wall). Foliar spraying boron is one option, but just confirm proper pH and ensure the nutes you are working with contain boron. Note: I know 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 = better stem elongation = 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 (I’d check macros and secondaries first before pointing the finger at cobalt, though).

Finally: Zinc!

We have arrived at our last micronutrient, zinc! Zinc is an important micronutrient from a growth perspective – Zinc in small quantities is needed to ensure appropriate growth and to prevent chlorosis. Like many of the other micronutrients, zinc should be in a chelated form (Zn EDTA for example). Zinc = improved yield = 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 possibility!

Final Thoughts

Dude, that was a lot of elements to discuss. The take home message here is: keep your pH at the 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 all the micronutrient deficiencies listed. Consolidation is always a nice thing!

Who is Dr. NPK? With a PhD in Chemistry from UC Irvine, Dr. NPK was instrumental in developing the Elite Nutrient line.  Learn more about him here.