That’s one I’ve spent the least amount of time reading on. I’m not sure what risks there are to oversupply since it’s usually so low.
In truth, skipping the plant prod and using Iron DPTA is even better. A few places suggest a 2:1 ratio of Fe to Mn, and I’d probably tend toward a higher ratio of Fe than Mn, because I think Mn is not shown to be inhibited by P.
Something like this is manageable too.
@lefthandseeds I find this all fascinating, and, simultaneously, I have almost no idea what half of this means. If you’d be so kind as to point me in the direction of just one resource to begin researching this approach, I’d be super grateful.
Finding the starting point is usually the most challenging part of learning something new!
Have you looked into Plantex CSM+B or maybe Millers Microplex?
In the planted tank world, these are usually what we use to do EI Dosing…
I think a really good resource for starting to learn a lot about plant nutrition is Manic Botanix:
I’d recommend checking out his articles on plant nutrition.
I haven’t checked those out yet. Are they easy to obtain in small-ish quantities?
Edit:
Herels the Plantex 0.2g/gal (which looks pretty similar to the plant prod)
The Miller’s Microprod looks like it needs to be used with another supplemental iron product, similar to Peters STEM. It might be workable, but I’m a little unsure about the equal rates of Zn and Cu.
Thank you kindly dude!
I think I’m going to trial the TM7/Iron DPTA/Boric Acid mix. All the Mo is going to come from the TM7, which is being used just below the recommended rates, so it’ll probably be ok.
One interesting thing about TM7 that isn’t provided by the other micros I have is cobalt… 
But I think if you add some iron and boron, you end up with a pretty close ratio to the leaf tissue sample sufficencies… so it seems like a potential winner.
Yeah usually we add in chelated iron on top of either of those. The millers is good but usually can’t use it as the high copper will kill any invertebrates, csm+b tends to be safer in that regard but neither should affect the plants.
For all those looking for a good, thorough primer on nutrient solutions, I just found this excellent pdf:
160825_manual_nutrient_solutions_digital_en.pdf (3.0 MB)
Yesterday, I had some concerns about using the sulfate forms of micronutrients in a recirculating nutrient solution. There is a section in there with some good explanations:
Other micronutrients with sulphate can be used as long as the pH is kept at 5.5.-7.0. The use of metal sulphates, however, will lead to losses of iron due to the exchange of Fe in the chelate by Cu, Zn and Mn ions. Depending on the pH, the losses of Fe can be as large as 20 to 50%. This loss can be compensated by increasing the supply of iron chelates as the pH rises, but could better be handled by using EDTA chelates of Mn, Zn and Cu. An additional benefit of metal chelates is that they contain less heavy metals than metal sulphates.
Also this table is good:
From what I’ve read, iron is especially difficult to supply, and pH is extremely critical to maintain, even for chelates. Iron DPTA is good for nutrient solutions, but if pH rises above 7, you can expect that you’ve likely lost your iron. Iron EDDTA is super expensive, but best to use if you’re in soil and are worried about your pH spiking up.
I think sulfates are fine for other micronutrients, except that iron will trade places with them – eg iron EDTA + zinc sulfate eventually ends up as zinc EDTA and iron sulfate, where it is much more likely to transform into something else and become unavailable.
Sulfates like in TM7 or Peters STEM are OK for foliar application, though TM7 is better, because humic acids can act as a chelator and make them more available to the plant, even as foliar. It also seems that foliar application is the best way to guarantee adequate micronutrients, including iron. But it probably shouldn’t be mixed with other foliar products, especially not ones containing calcium or phosphorus.
So, I’m back to square 1 on mixing micros. I don’t think it’s prudent to combine either TM7 or Peters STEM with chelated iron. Rather than going that path, it seems best to use chelates only. DPTA for iron, EDTA for Zn, Mn, Cu. Boron and Mo are fine as boric acid and sodium molybdate. Back to shopping…
I like reading this link. It has some good information about tomato nutrition. I think learning from other plants can give some ideas for cannabis as well.
- Young plants require and should be provided with lower nutrient concentrations than mature plants, to prevent plants from becoming too vegetative.
- Plants in early fruiting stages require increased levels of specific nutrients like nitrogen (N), calcium (Ca), and potassium (K) because the developing fruits demand greater amounts of these nutrients.
- Mature fruiting plants require the highest levels of nutrients to promote plant growth and fruit development, as well as an appropriate balance of specific nutrients to ensure high fruit quality.
I’ve noticed that some very reliable places usually keep N low during veg, which is odd. There’s a reason though. They give it further down in the page –
In young tomato plants (up to and including Stage 2), the primary concern is limiting the concentration of nitrogen (N) compared to the concentration used for mature plants. Too much N will cause the plants to be overly vegetative, resulting in thick stems, burly and curled leaves, and most importantly, reduced flowering
Later, they recommend only using 90ppm of N in early stages, and increasing during fruiting.
Here’s some formulas from Southern Ag 5-11-26:
In their general schedule, their recommendation for a standard 3/2/1 style recipe is mostly like you’d expect, except a little less Mg that we typically use. 8lbs in 1000 gal is 3.6g per gallon. So their label is a 3.6g-2.4-0.9 ratio, and recommend adding iron in some cases (sequestrene 330 Fe - Iron DPTA).
So you can see, that in their “Early” schedule, there’s only 100ppm N – mirroring the sentiments from OSU.
In their other recipes, they’re also using potassium sulfate and calcium nitrate. Notice that in their “Later” formula, they increase calcium nitrate to 3.6g and add around 0.5g/gal potassium sulfate and 0.23g/gal iron DPTA.
Like the OSU paper said, in the early fruiting stage, the plant needs a lot of N, K and Ca. And in the 5-11-26 formula, those are the big numbers supplied. You don’t normally think of high N in veg for cannabis though. But it’s interesting how they reverse it from how we typically think of growing – which is higher N in veg and lower in flower.
Nice mix. I like the numbers.
That is a very good article. I hate I do this on my phone. I’m into making your own soil. I do reuse my soil. Not always. The last run I didn’t. This one I will be mixing with new happy frog. I’m growing with advanced nutrition organic line right now. Got a great deal on it. I like the fish stuff. Will never get fish it again. Don’t trust it. No seal. Just for the moment. Micro for old used soil. Bone meal is great to recharge for cheap. Plant tone works also. She will get hot. Ppm will run high. KISS is very correct. A lot of products out there. Just have to be cautious. I get stuff all the time that is very hot. But works at different times. 5-11-26 is nice
Don’t want to clog up your thread, but the micros discussion had me wondering when one should supplement with micros. Say a bit of tm7 mid flower for a push to the end?
It probably depends on a lot of things. I think if you are feeding from a reservoir it could do more harm than good. Any chelated iron you use will interact with copper and zinc sulfates and probably do more harm than good. In general, I’d probably suggest sticking to weekly foliars with TM7 before there’s too much budding.
I’m not sure extra micros are needed at the end, if they are supplied in the right amounts. I’m not yet sure what the right amounts are, but most nutrient formulas are all over the map. There’s a few things to suggest that more boron is beneficial, and possibly also zinc. But if you start from a commercial formula, it’s hard to adjust micros safely. The amounts are so small that unless you’re using a precision scale, you could easily overshoot them.
Something I’ve been thinking about a lot recently is this idea of balance of ammonium and nitrate in solution.
It has to do with rhizosphere pH, and also pH of your solution if you’re in recirculating like me. Here’s an exerpt:
The second method is to control the pH by increasing the ammonium level. This is done by adding increased amounts of ammonium to a nutrient solution when the pH in the root zone is rising, which usually occurs as a result of high vegetative crop growth rates. The roots will take up the NH4+ ions and release acidifying protons (H+) into the root zone. This acidification of the root zone will create a beneficial environment for the uptake of nutrients by the plant.
In hydroponic growing systems, the proportion of ammonium cations should be limited to 5-15% of the total nitrogen in the solution. A maximum of 1-1.5 mmol/l (14-21 ppm N) NH4+ in the nutrient solution is acceptable; if higher, the pH will drop too much.
And here’s another one from Nutrition of Substrate-Grown Plants (another good resource on plant nutrition)
The nitrogen source may affect the rhizosphere pH via three mechanisms: (i) displacement
of H+/OH− adsorbed on the solid phase; (ii) nitrification/denitrification reactions; and
(iii) release or uptake of H+ by roots in response to NH4 or NO3 uptake, respectively.
Mechanisms (i) and (ii) are not associated with any plant activity, and affect the
whole volume of the fertigated substrate, whereas mechanism (iii) is directly related
to the uptake of nutritional elements, and may be very effective because it affects a
limited volume in the immediate vicinity of the roots
Here we get some idea of what having too much NH4 does to the root zone. With 3x as much NH4 as NO3, over time the pH falls dangerously low (pH ~4). If roots take up NH4+, they give back H+, which causes the pH to drop. Similarly OH- for NO3- absorption:
https://scienceinhydroponics.com/2017/03/nitrate-ammonium-and-ph-in-hydroponics.html?print=print
plants will always compensate ion absorption by releasing a pH altering ion of the same charge. If a plant absorbs nitrate (NO3-) it will release an OH- ion in order to balance the charge. This ion will increase the pH. The same happens when the plant absorbs a cation – like K+ or Ca+2 – as it will release H3O+ ions in order to compensate (one in the case of K+ and two in case of Ca+2). However plants do not absorb all ions equally and therefore if there is more cation than anion absorption pH will decrease while in the opposite case pH will increase.
And this is especially interesting to not:
It is also important to note that you cannot easily affect ion absorptions by shifting solution concentrations. Ammonium affects the pH quite directly because adding more ammonium to the solution almost immediately adds that ammonium to the plant’s cation absorption – because it’s taken up very readily – but adding other cations might not increase their absorption because either environmental or plant regulatory mechanisms may stop this from happening. For example increasing potassium may not increase the overall size of the cation absorption column because the plant might simply compensate by reducing calcium absorption. Such a compensatory mechanism does not exist for ammonium, reason why it is so effective in changing the relative size of one column against another.
So ammonium is like the ark of the covenant to plants. Once it’s there, there is no way for it to unsee the ammonium, which could lead to face-melting effects if oversupplied.
One thing that I think is important to note is that in synthetics, much of the NH4 budget comes from calcium nitrate (14.4% NO3, 1.1% NH4). However, if we start using Calprime or PureCal to increase calcium rates, those fertilizers do not contain ammonia, and it may not be supplied. One option is to add ammonium sulfate – however, for some reason, I’ve read this has ~1.5x the acidifying amount as compared to MAP (monoammonium phosphate) or ammonium nitrate (which you can’t buy anyway because it go boom).
However, I think it’s probably important to “get it right” in a nutrient formula. I’m not sure what the proper ratio is, but I’ve seen it used as 1:14 (from calcium nitrate in 321-style formulas) and 1:7 (eg Veg+Bloom). Master Blend 4-18-38 has a 1:7 ratio, so when used with calcium nitrate is somewhere in between, but closer to the calcium nitrate ratios.
If using calcium nitrate as the primary source of nitrogen, then there may be no need to make adjustments; however calprime and purecal have no NH4, so adjustments could be necessary when using these fertilizers.
In summary – adding NH4 can help offset rising pH in root zones and nutrient solutions; however, because there is no alternative cation antagonism and it is easily absorbed, it can easily lead to oversupply and symptoms of N toxicity. One should also be careful when using fertilizers like MAP in bloom where this could cause issues with N oversupply. However, finding the right balance of NH4/NO3 may be critical to rhizosphere pH, which benefits absorption, especially of micronutrients.
Been having this exact issue now for about 2 weeks. A friend on another forum talks about balancing nitrate and ammonium to balance rhizosphere pH but, I always figured ammonium was best in a soil setting so I try to avoid using it aside from the 1% in Ca nitrate. Been rethinking this though so I can get a better handle on rhizosphere pH.
I had also dismissed it as being most important for soil. It’s not something I ever thought about too much until I started looking at these calprime/purecal fertilizers. Normal calcium nitrate contains some amount of CAN - calcium ammonium nitrate, which is what is eliminated in calprime and purecal.
So that gives you independent control of nitrate and ammonium… but then you have to consider how much ammonium you want for pH control. My gut says that because pH usually drifts upwards, you likely want the most acidifying effect with the least amount of ammonium. So it could be better (although more expensive) to use calprime and ammonium sulfate, rather than calcium nitrate.
each mole of nitrogen as ammonium sulfate produces four moles of hydrogen, while each mole of nitrogen as urea or ammonium nitrate produces only two moles of hydrogen. This suggests that ammonium sulfate is two times more acidifying than ammonium nitrate or urea
So this seems to suggest that ammonium sulfate is the best source for acidification, and then you can either supply less NH4 overall, or get more acidification in the rhizosphere.
Anyway, this review paper I’m reading and a bit of googling seem to suggest that NH4 concentration is potentially pretty important for soilless culture as well.
I’m also wondering how do you balance rhizosphere pH while simultaneously trying to decrease N for mid and late flower?
You’re asking all the right questions I think. Last night I was just considering cation/anion balance, and now is maybe the perfect time to think about it.
I think there’s quite a few things about this picture that help answer the question. On the left are the cations (K, Ca, Mg), and on the right are the anions (N, P, S). If you have more absorption of anions than cations, you get a rise in pH. So this is when you have to add more H+ by using an acid (usually phosphoric or sulfuric). If you have more absorption of cations than anions, you get a drop in pH.
One thing to note about this plot is that it is showing relative absorption and not relative amounts. I think this is important, because mineral uptake of Ca and Mg is known to be slow, and I think it is because of this that in general, pH tends to rise.
Another thing that is important is that plants can’t pick and choose what nutrients to absorb. Maybe they can do some modulation between cations or anions as groups, but in general, I think the plant will reduce all cation absorption, reducing absorption K, Ca and Mg together, rather than separately (and same for anions).
Ammonium utilizes a different pathway than the other cations, so it is a unique tool in that sense. But on the other hand, the plant cannot stop its absorption at all, so it can also be risky to use too much.
Salts are just a combination of cation + anion, so instead of reducing nitrate, for instance, you have to consider what you want to substitute it with.
Potassium Nitrate
Potassium Phosphate
Potassium Sulfate
Calcium Nitrate
Calcium Phosphate (
insoluble)
Calcium Sulfate ( insoluble)
Magnesium Nitrate
Magnesium Phosphate
Magnesium Sulfate
Ammonium Nitrate ( strictly regulated, so not easily available)
Ammonium Phosphate
Ammonium Sulfate
So instead of thinking about reducing nitrate, you have to think about what you want to convert it to… either more sulfate or more phosphate.
Since nitrate does not have the same mechanism of absorption as phosphate, then if you switch some nitrate for phosphate, you are also changing the absorption balance, because they are absorbed different.
The cation–anion balance in plant tissues is maintained
by diffusible and non-diffusible organic and inorganic ions, and has been found to be
notably affected by the sources of N nutrition
Then there is also their potential for reactions to consider
Nitrate, the main N source for soilless-grown plants (Sonneveld, 2002), is hardly
ever involved in adsorption or precipitation reactions; therefore, the concentration of
NO3− in the irrigation water and its actual concentration in the vicinity of the roots
are quite similar. In contrast, P availability to plant roots is time dependent, as a result
of adsorption and precipitation reactions (Chap. 6). Potassium ions are hardly ever
involved in precipitation reactions, but may be adsorbed on negatively charged sur-
faces. Therefore, the difference between the K concentrations in the irrigation solution
and the rhizosphere lies between those between the respective NO3− and P concen-
trations. Consequently, it can be expected that the impact of fertigation frequency on
the uptake of nutritional elements by plants will be related to both their mobility and
their availability, as indeed has been reported
And also differences based on fertilization frequency
Although the effects of irrigation frequency on nutri-
ent concentration in soilless-grown lettuce leaves presented in Fig. 8.13 followed the
expected order of P > K > N, the magnitudes of the nutrient increases in the plant
was found to be closely related to the fertilisation level.
…
The increases in the leaf P and K concentrations were attributed to both direct
and indirect effects of irrigation frequency on the P and K concentrations at the root
surface. The direct effect is the frequent elimination of the depletion zone at the root
surface by the supply of fresh nutrient solution during and soon after the irrigation
events. This supply was fully available to the roots soon after the irrigation events,
at which times its uptake rate behaved purely in accordance with the Michaelis–
Menten equation (Eq. [4]). Moreover, a higher irrigation frequency maintains higher
dissolved P and K concentrations in the substrate solution, by shortening the period
during which precipitation takes place.
This indirect effect can be mitigated, I believe by using polyphosphate fertilizers, as opposed to orthophosphate. Anyhow, I think it is not easy to answer, because it involves so many different considerations, down to how often you intend to fertilize.
It seems to me that it is not a question of reducing nitrogen, so much as a question of determining what is a better anion balance. In other words, if I reduce nitrate, will the plant be happier with more phosphate or more sulfate? And then, how does this affect the cation-anion balance, so that I can determine the proper amount of ammonium?
It’s not so easy to answer…
A safe strategy might be something like this –
You choose to decrease nitrate and increase sulfate. So maybe that means you use more potassium sulfate and less potassium nitrate. Now you account for the increase in sulfate by reducing the sulfate as well by using less ammonium sulfate, keeping the same proportion between ammonium:nitrate (eg fixed at 10%).
So in the end, you have minor differences in sulfate, but overall less nitrogen in both nitrate and ammonium.
You know how this sounds, right? I mean Saturday evening at home 
