Fertilizers explained (2-part presentation) -- with 6/2023 update

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Steve Johnson
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Fertilizers explained (2-part presentation) -- with 6/2023 update

Post by Steve Johnson »

Fertilizers explained (Part 1)

After I joined the forum in November 2011, I wanted to learn about the different growing practices being followed by members with a level of experience I simply didn't have at the time. The subject of fertilizers came up fairly often, but I didn't find anyone who could properly explain all the ins and outs of ferts that are most suitable to the needs of our cacti. That changed when MikeInOz joined the forum in 2018, so endless amounts of credit go to him -- horticulturalist with a deep knowledge of cacti and succulents, and the best explainer of fertilizers we could ever hope to have. I learned a lot from him, and I'd like to "pay it forward" by passing the knowledge along for the benefit of other members who can use it to improve the growing quality of their plants.

How fertilizers are reported

The reporting is done through your fertilizer's label -- all fert manufacturers report N as the total amount of Nitrogen available to our plants. In Australia, ferts are reported in elemental P and K values. In other countries (Ireland and the UK, for example), the ferts report P as P2O5 and K as K2O along with their elemental values on the product label. If the elemental P and K values aren't on the label (as is the case with manufacturers reporting only P2O5 and K2O in the US), use the following calculations:

%P2O5 x 0.436 = %P
%K2O x 0.83 = %K

While the Oxygen in P2O5 and K2O helps to support the plant's overall heath, it has no nutrient value, so all we're concerned about is getting the right amounts of the elemental P and K available to our cacti and succulents.

NPK ratio

This ratio determines whether you have well-balanced or unbalanced proportions of N, P, and K in your fert. The ideal NPK ratio for cacti and succulents is 1:0.4:1.1-1.7. Contrary to what you may have heard or read elsewhere, high-Phosphorus ferts should be avoided -- when P is higher than N, poor root growth, reduced stem growth, and reduced flowering (or no flowering at all) will be the eventual consequence of the plant's longterm exposure to a high-P fert.

Evaluating the fertilizer's NPK ratio

My fert of choice is Dyna-Gro All-Pro 7-7-7, so we'll use it as an example. The guaranteed chemical analysis:

Image

Available N = 7%
P2O5 = 7% x 0.436 = 3.052% elemental P available to the plant
K20 = 7% x 0.83 = 5.81% elemental K available to the plant

The true NPK value for the 7-7-7 is 7-3.052-5.81. Using N as a constant of 1, the NPK ratio is 1:0.44:0.83 -- the balance between N and P is pretty much ideal, but I had to bring the ratio of K up to the 1.1-1.7 range. If your fert strikes the right N-to-P balance, but you find yourself in a situation with K that's not as high as it should be, the next step is...

Addressing the K deficiency

I did that with a 0-0-52 Potassium sulfate (K2SO4) supplement, and you can too, although the amount required will depend on the fert. We'll discuss it in more detail a bit later.

Important minor nutrients
  • Calcium and Magnesium. Okay, maybe not so minor -- an enduring myth (which I fell for until Mike busted it after he joined the forum) is that Calcium inhibits cactus growth. In fact, it's the exact opposite, and he's spot-on when he says that "there's no such thing as too much Calcium". However, Ca needs to be balanced with Mg. Theoretically the "ideal" Ca-Mg ratio is 4:1, although I'm not sure if we have to be all that strict about it. A more detailed look at Ca and Mg is beyond the scope of this presentation, but if you'd like to dig deeper, go here and start digging:

    https://www.cactiguide.com/forum/viewto ... 54#p394954

    Are your plants getting enough Ca and Mg? If not, what can you do about it? Both questions are worth asking, and you'll find the answer to question #2 when you follow the link.
  • Sulfur. Although S is a minor nutrient, it's also important, and S deficiency shows up in the form of abnormally pale-looking cacti. If you're adding a K2SO4 supplement to address a K deficiency in your fert, the S is bonus.
Micronutrients

The more I thought about what I've learned from Mike, the more I came to realize that fertilizers are nutrient systems, not just a bunch of unconnected parts. If your fert doesn't include micronutrients, it'll be missing some of the parts that keep the system functioning to optimal effect. The full spectrum of nutrients you see in the 7-7-7 is a "gold standard" you can apply when you evaluate your current fert. If yours doesn't have micronutrients on the label, it's time to look for a better one.

Dosage

Dosage = amount of fertilizer going into your watering solution, which in turn is taken up by the roots of your plants. How do we know if the NPK dosage in the watering solution is not enough, too much, or just right? For the mathematically inclined, we can get the answer in terms of parts-per-million. Once again, we'll use the Dyna-Gro All-Pro as an example -- I dilute 1/2 teaspoon per gallon of water. 1 gallon = 1536 half-teaspoons.

7% N = 70,000 ppm/1536 = 46 ppm
3.052% P = 30,052 ppm/1536 = 20 ppm
5.81% K = 50,810 ppm/1536 = 33 ppm

Cacti and succulents are adapted to living on "thin soup", so they will grow well with a steady supply of N and P at this dosage. But we still need to increase the K, so I'll give you the details on that in the next section. Before we get there, here's a table showing the proper dilutions for ferts with 5%, 7%, 10%, and 20% N in teaspoons per gallon and milliliters per liter. Note: The table applies only to liquid fertilizer concentrates. Unfortunately, dilutions using dry ferts are beyond my pay grade!
Image
When you look at those ppm numbers, you may wonder if the N dosage is too high with the 5%, 10%, and 20% dilutions. Actually, it's quite acceptable -- anything below 90 ppm should be fine. With that said, cacti and succulents tolerate underfeeding a lot more than they do if they're overfed, so when in doubt, go with dilutions that are just a shade below what you see for 5%, 10%, and 20% N. (In my humble opinion, the dilution for 7% N is just right.)

Potassium sulfate

Thanks to Jerry Smith (AKA jerrytheplater) for helping me figure this out -- here are the instructions on how to supplement a 7-7-7 fert with Potassium sulfate:
  • First create a stock solution by adding 7 grams of 0-0-52 K2SO4 powder to a 1 gallon jug of rainwater or distilled water (not tap water! RO water is acceptable). The powder doesn't dissolve instantly, so give it plenty of time to go into solution. Hint: If you can heat the jug in an oven at 150F for 1/2 hour, turn off the heat and let it sit in the oven for an hour, then take it out, you're set. Once the K2SO4 has gone into solution, it'll stay in solution.
  • For the watering solution -- fill a 1-gallon jug with water halfway. Add 1/2 tsp. 7-7-7 and 5 fluid ounces of stock solution, then fill the jug up to the fill line. Cap it, shake well, and water your plants.
The watering solution contains 33 ppm K from the 7-7-7, the other 36 ppm is provided by the 5 fl. oz. of stock solution, so that gives you a total of 69 ppm K -- exactly 1.5 times higher than N.

Nice thing is that cacti and succulents aren't precision instruments, so the 1.1-1.7 range on the K side of the ratio gives us a fair amount of "wiggle room". Although I use 0-0-52 K2SO4 for my stock solution, it doesn't matter if you prepare yours with 0-0-50 (the most common) or 0-0-53 (less common, but apparently you'll see it more often than 0-0-52) -- your plants won't know the difference. If your fert's K2O already places elemental K in the 1.1-1.7 range, you won't need a stock solution. However, if its percentage of K2O is lower than its percentage of N, you'll need to increase the amount of K2SO4 in your stock solution. For example -- in a 7-8-6 fert, you should prepare a 1-gallon stock solution with 8 grams of K2SO4. Another hint: Use a digital kitchen scale reading in grams to measure the amount of K2SO4 powder going into your stock solution. A certain amount of precision is helpful, and measuring spoons won't be precise enough for our purposes. For even more precision, use a scale measuring in 10ths or 100ths of a gram. (Scales with that kind of precision aren't expensive, and you can buy them online.) In case you need it, here are examples converting grams per gallon to grams per liter with stock solutions that supplement 7-7-7 and 7-8-6 ferts:
  • For 7-7-7 -- 7 g./gal. = 1.85 g./L or round up to 1.9 g./L.
  • For 7-8-6 -- 8 g./gal. = 2.11 g./L or round up to 2.2 g./L.
By the way, the rounding up gives you that "wiggle room" I just mentioned. And if your fert's N-to-K ratio is different from what you see in the examples, use these calculations to recalculate the right amount of K2SO4 in the stock solution matched to your particular fert. That may be the hard part (although not so hard if your basic math skills are good), so here's the easy part -- let the amount of stock solution going into your watering solution be a constant:
  • 5 fl. oz./gal. or 39 mL/L.
Those dilutions will be the same regardless of how much K2SO4 you have in the stock solution.

The benefits of higher K are significant, and if your fert comes up short on the K, they make a good argument in favor of supplementing it with Potassium sulfate:
  • Stronger, healthier roots.
  • Better stem growth and stronger, more abundant spine formation in species that are sensitive to the effects of K deficiency. Hard to describe in so many words, but if your powers of observation are good, you'll notice significant "before and after" improvements when you see what your cacti look like after you start applying the supplemental K.
  • Better resistance to pests and diseases. While it's not a 100% guarantee that you'll never see either problem, higher K greatly improves the odds that you won't have much trouble with both.
  • More prolific flowering -- this debunks the "higher P" myth being promoted on other Websites. And sadly, there are "expert" growers who still believe it.
Truth be told, 1 growing season of Potassium sulfate supplementation may not be enough to see a dramatic improvement in some or most of your cacti (it depends on the species), but give it another year and you'll be pleasantly surprised by the results.

Frequency

Frequency = how often you should fertilize when you water. If you're growing cacti in a completely soil-free hydroponic medium (like the 60% pumice/40% granite gravel mix I use for 64 of my 68 cacti), you'll need to fertilize every time you water. If your mix contains a certain amount of soil, you won't have to fertilize as often. These guidelines are just a guess on my part:
  • 10%-25% soil in the mix -- fertilize with every other watering.
  • 40%-50% soil in the mix -- fertilize with every 3rd or 4th watering.
If you have more accurate recommendations based on your own experience, let me know what they are via PM.

A note to beginners: Cacti should be fertilized only in the growing season. If you live in a tropical climate, you won't have that limitation because your growing season is year-round.

Succulents are a different kettle of fish (so to speak) -- I have no experience with them, so I'll leave the fertilizer routine up to the succulent people who grow them.

An avoidable problem

Nutrients not taken up by the plants are left behind as fertilizer salts in one's potting medium, and salt buildup can be a problem if it's allowed to go unattended. Maybe not this year, maybe not next year, but a few years from now, you may find that your cacti stall out and go into a slow decline. The best way to avoid this problem -- flush out your pots with rainwater or distilled water and nothing more once a year in the growing season. Here's the procedure:
  • Water deeply until it's running down out of the pot like a faucet.
  • Wait for an hour and flush again.
  • Wait for another hour and flush for the 3rd time.
Any salt buildup that may have been in the pot will be gone. If you make a habit of doing this every year, you'll get happy, healthy cacti year after year.

Liquid concentrates vs. slow-release fertilizers

Slow-release ferts have an obvious advantage over having to prepare a watering solution every time your cacti need to be fertilized. If you happen to live in Australia or New Zealand, Scotts Osmocote has a cactus and succulent formulation just for you. If you live anywhere else, sorry -- that formulation isn't being sold anywhere else either. But believe it or not, there are slow-release ferts for orchids and bromeliads which are suitable for cacti as well. Here's an example of one you can find on Amazon:

https://www.amazon.com/Fertilizer-13-3- ... 300&sr=8-5

If a slow-release fert's P is actually too low, add just a little bit of monopotassium phosphate to your watering solution.
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Although I left a detailed discussion of Calcium and Magnesium up to the link I gave you earlier, I'll touch on how I'm approaching the matter...

Going back to the Dyna-Gro 7-7-7's product analysis, you'll see that it contains 2% Ca and .5% Mg -- good balance, but before I learned about the importance of Calcium from Mike, I didn't realize that my cacti hadn't been getting enough. To correct the Ca and Mg deficiency, I doubled the amount with 1/4 tsp. of a Nitrogen-free CalMag supplement per gallon of watering solution.

After 2 years of the Potassium sulfate supplement and only a year of adding CalMag to the nutrient mix, the improvements have been amazing. The goal (and I may be on the way to achieving it) -- cacti able to reach their genetic growth potential with a full spectrum of well-balanced nutrients being delivered at a low but steady level. We're not quite done with this presentation, so stay tuned for Part 2 as I show you how to make the most out of the Nitrogen in your fertilizer -- and it's something you may not even know.
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Fertilizers explained (2-part presentation)

Post by Steve Johnson »

Fertilizers explained (Part 2)

The 2 most common forms of Nitrogen in liquid fertilizers are Ammonium (Ammoniacal) N (NH4) and Nitrate N (NO3). NH4 is taken up immediately by the plant, but NO3 must be reduced to Ammonium in the plant's tissues -- this requires Molybdenum (Mo) for the reduction process. Liquid ferts are mostly Nitrate, and ideally they should include approximately 0.008% Mo. However, the reality can be quite different. For example...

As good as it is, the Dyna-Gro 7-7-7 comes up way short on the Mo -- 0.0009% x 10,000 = 9 parts-per-million. Going by my standard dilution of 1/2 teaspoon per gallon, 9 x 1536 = 0.006 ppm, or 6 parts-per-billion. I discussed the matter with our resident horticulturalist MikeInOz, and I asked him about how much Mo cacti need for more efficient Nitrate-to-Ammonium reduction. Here's his answer:
MikeInOz wrote: Wed Jan 25, 2023 2:36 amAll hydroponic solutions for various crops contain 0.05ppm Mo. It does not seem to vary among different crops so perhaps that is a standard optimum amount. Aim at that and you should be fine.
Okay, so we have a target amount -- 50 ppb. If your fert has just a scant trace of Mo (or no Mo at all), you can supplement it with a Sodium molybdate stock solution and the right amount of stock solution going into your watering solution. As math teachers tell their students, "show your work!", so I'll show mine as we go through the steps. Good news is that I'm doing the math so you don't have to!

Sodium molybdate (Na2MoO4) in powder form is easily available online, and it's not that expensive. Make sure that you're getting Na2MoO4 with a guaranteed analysis of 39.5% Mo. For the stock solution calculations, I went to the Calculate This website's ppm calculator (https://calculate-this.com/ppm-of-solut ... lator#calc). The calculator gives us 2 choices -- US (ounces to gallons) and metric (grams to liters), so we'll go with metric for the most precise calculations possible.

Just a reminder: For your stock solution, do like you did with the Potassium sulfate stock solution -- start with distilled water or rainwater (not tap water! RO water is acceptable).

US growers

Create a half-gallon of stock solution by diluting it with 0.1 gram Na2MoO4. This gives you .0395 g Mo. Using this handy-dandy online unit converter (http://www.unitconversion.org/unit_conv ... olume.html), we know that 0.5 gal. = 1.892705892 L
The ppm calculator shows that .0395 g Mo going into 1.892705892 L gives us 20.87 ppm Mo in the half-gallon of stock solution. The next step is calculating the amount of stock solution per gallon of watering solution:

1 gal. = 768 teaspoons
20.87 ppm/768 = 0.0272 ppm (27 ppb)
That's 1 tsp., so if you add 2 tsp. of stock solution, you'll have 54 ppb Mo in your gallon of watering solution.

Non-US growers

For you metric people out there, the calculations are a lot easier...

Stock solution per liter of water
Dilute 0.1 gram Na2MoO4 -- this gives you .0395 g Mo.
.0395 g/L = 39.5 ppm Mo

Amount of stock solution per liter of watering solution
39.5 ppm/1000 mL = .0395 ppm (39.5 ppb)
39.5 x 1.5 = 59 ppb
Add 1.5 mL stock solution per liter of watering solution, and you'll get 59 ppb Mo.

Note: For those of you who don't already have one, buy a digital scale reading down to .01 or .001 g. Easily available online, and they're not expensive.

Could the amount of Mo in our watering solutions be a little too high? Actually, no...

From Promix (https://www.pthorticulture.com/en/train ... t-culture/):
  • "Molybdenum toxicity is very rare and, in some crops, the tissue can have several thousand ppm and still not show symptoms. In a few rare cases there has been report golden yellow appearance of the leaves."
I realize that refers to crops, but it won't be any different for cacti. However, I wouldn't recommend taking a chance on going with substantially higher amounts.

How many people know about the Nitrate-Molybdenum connection? My guess is -- not many, so I'm glad to share this extra tidbit with you as the presentation concludes. I hope you'll get a lot of good use from it. All the best, and happy growing, everyone!

Steve Johnson
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Re: Fertilizers explained (2-part presentation)

Post by Aztekium123 »

Thank you for sharing knowledge. This is a very useful article for me.
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Re: Fertilizers explained (2-part presentation)

Post by Steve Johnson »

Aztekium123 wrote: Sun Jan 29, 2023 11:32 am Thank you for sharing knowledge. This is a very useful article for me.
You're welcome! :D

As I've come to find out over the years, "common knowledge" (like common sense) isn't all that common. It's also a great way to spread myths and misinformation on the Internet, so Mike did us a huge service by debunking myths and dispelling misinformation with his expert knowledge of how fertilizers work with regard to our favorite plants. That knowledge shouldn't be buried, hence my reason for posting the presentation as a sticky. If any of you know someone who isn't on the CactiGuide forum, please feel free to email them with the link and help spread the knowledge. The forum is a free service too, so we'll invite them to join the party!
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Re: Fertilizers explained (2-part presentation)

Post by Minnesota »

Hey, Steve!

All I can say is...wow. Just, wow. Magnificent job of reducing enormous amounts of chemistry and plant biology into a fundamental presentation. I've followed a few bits in another post between you, Jerry, and Mike, and the details of the conversation were boggling. This distillation of the basic premises, minus the deep-dives, is excellent. I can't wait to start the evaluative parts tomorrow--my fertilizer, my dilutions, my watering patterns, etc.

Simply magnificent. Most well done. Thank you. :D

Bret
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Re: Fertilizers explained (2-part presentation)

Post by Steve Johnson »

Minnesota wrote: Mon Jan 30, 2023 3:04 am Hey, Steve!

All I can say is...wow. Just, wow. Magnificent job of reducing enormous amounts of chemistry and plant biology into a fundamental presentation. I've followed a few bits in another post between you, Jerry, and Mike, and the details of the conversation were boggling. This distillation of the basic premises, minus the deep-dives, is excellent. I can't wait to start the evaluative parts tomorrow--my fertilizer, my dilutions, my watering patterns, etc.

Simply magnificent. Most well done. Thank you. :D

Bret
My pleasure, Bret! :D
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Re: Fertilizers explained (2-part presentation)

Post by SDK1 »

Steve Johnson wrote: Sun Jan 22, 2023 6:53 am
This ratio determines whether you have well-balanced or unbalanced proportions of N, P, and K in your fert. The ideal NPK ratio for cacti and succulents is 1:0.4:1.1-1.7.
Steve Johnson wrote: Sun Jan 22, 2023 6:53 am
Theoretically the "ideal" Ca-Mg ratio is 4:1...
I'd love to know where these values (the ratios) are sourced from.
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Re: Fertilizers explained (2-part presentation)

Post by Steve Johnson »

SDK1 wrote: Tue Jan 31, 2023 11:57 pmI'd love to know where these values (the ratios) are sourced from.
See this:

viewtopic.php?p=376328#p376328

The "ideal" Ca-to-Mg ratio of 4:1 is only theoretical (and I said as much in Part 1). The reality is a bit more complicated, which is why I have the link to the "CalMag of my dreams?" thread in Part 1. I realize that it's a long and detailed thread, so here's a post from Mike which explains the situation better.

viewtopic.php?p=398307#p398307
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Re: Fertilizers explained (2-part presentation)

Post by MikeInOz »

SDK1 wrote: Tue Jan 31, 2023 11:57 pm

I'd love to know where these values (the ratios) are sourced from.
In my book on growing media the following quote - ''Media in which plant growth is excellent tends to have extractable Ca/Mg ratios of about 3 to 4''.
Meaning - Calcium 3-4 times that of Magnesium. It is not critical but ''where high levels of K are applied the ratio should be lower rather than higher. A Ca/Mg of 2 rather than 5''.
''High levels of K'' could mean a K/N ratio of 2 or more. Given all that, the ''3 to 4'' seems to be a pretty good number for us
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Re: Fertilizers explained (2-part presentation)

Post by SDK1 »

Steve,

Thanks for the links but I'm afraid I still don't see where the "1.0 : 0.4 : 1.1-1.7" value is originating from. Since this ratio is what all of the discussions about ferts and pH are built upon, I'm very curious what the source of the ideal ratio for NPK is.

Mike,

Thanks for that, could you share the title and author of the book?
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Re: Fertilizers explained (2-part presentation)

Post by MikeInOz »

SDK1 wrote: Wed Feb 01, 2023 3:55 pm
Mike,

Thanks for that, could you share the title and author of the book?
''Growing Media for ornamental plants and turf''
K.A. Handreck and N.D. Black
University of NSW press.
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Re: Fertilizers explained (2-part presentation)

Post by Steve Johnson »

SDK1 wrote: Wed Feb 01, 2023 3:55 pm Steve,

Thanks for the links but I'm afraid I still don't see where the "1.0 : 0.4 : 1.1-1.7" value is originating from. Since this ratio is what all of the discussions about ferts and pH are built upon, I'm very curious what the source of the ideal ratio for NPK is.
I got those ratios from Mike, and this is where the education I got from him started back on 8/21/20:

viewtopic.php?p=377330#p377330

"Cacti and succulents do best with a 1:1:1 NPK ratio or something close to it" -- that was "conventional wisdom" I got from cactus growers who didn't have professional horticultural experience. Mike does have that experience, and since you're looking for sources, he just gave you a good one.

My original contention was that K should be 1.5 times higher than N based on what I learned from him in 2020. The reason why you're seeing a range of 1.1-1.7 instead is this:
MikeInOz wrote: Tue Jan 17, 2023 5:48 am
Steve Johnson wrote: Tue Jan 17, 2023 4:31 am I went on the National Library of Medicine's PubChem website and got the molecular weights of K, S, and K2SO4. The precise calculations show that 1 gram of pure K2SO4 contains 44.87% K and 36.81% S. Of course that applies to 0-0-52, but from what I've seen online, 0-0-50 is a lot more common, and I also see 0-0-53 from a few sources. What's the difference in terms of K and S percentages? Reason I ask is that I want to get the dilutions right for 1-gallon stock solutions with 0-0-50 and 0-0-53 -- it'll come in handy if the people I'm trying to help can't get 0-0-52. I'm also trying to come up with the right ppm numbers for K in the stock solution -- important since the amount of stock solution going into a watering solution determines whether we get the N-to-K balance (K 1.5 times higher than N) right or not.
My text book says K2SO4 = K-44.9 ; S-18.4 I don't think it matters too much what you use. K/N ratio of over 1 will be ok 1.2 or 1.5 or 1.7. all good.
You'll see his response reflected in part 1 of my presentation.
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Re: Fertilizers explained (2-part presentation)

Post by SDK1 »

Mike,

Thanks so much for that, always love to have another book to add to the queue and I've not read that one yet. It's interesting that the percentage of K is listed as 5.2% in the table from the post of yours Steve linked to as I've always seen it much closer to 2%. This has usually segued into much of the rationale for using any variety of a 3:1:2 fertilizer formulation as a broad all-purpose use fertilizer. It'll be fun to read which plants they used as sources for tissue analysis (I'm just assuming for now that's where the 5.2% value is originating).

Steve,

Thanks for the background. The amount of misinformation out there regarding ferts, particularly the oft-repeated advice of 1:1:1 ratio being the gold standard, is such a problem, especially in hobbyist circles. The effort you've put into getting in to the nitty gritty is admirable. I'm going to dig into Mike's book when I have time but who knows when that'll be.

In the meantime I thought I'd share some papers/research/other fert threads I've found useful over the past couple years or that I've been meaning to sit down and read. Having a full time job and 2 kids under 2 means I'm just a bit tired kind of... always.

Park S. Nobel has done a lot of great research over the years with cacti/succulents and a few of their papers aren't paywalled anymore.

The first is one of my earliest finds. I find the tissue analysis tables quite helpful/interesting and I think the values line up rather well with your assessment of 1:0.4:1.1-1.7. (Edit: I generally follow the idea that it's best to supply nutrients in the amount they're being used by the plant and tossue analysis of the plant is how that's derived) I also find the rather strong negative reaction of cacti to Na rather interesting, seems they're more sensitive than leafy plants even. The PDF download is at the bottom of the page.

- <BOGUS PAYWALL>https://bsapubs.onlinelibrary.wiley.com ... .tb12473.x <paywalls are the devil, the authors don't even see any money from them>

Non-paywalled link: https://www.eeb.ucla.edu/Faculty/Nobel/ ... 20Ecol.pdf

This next one builds off of Nobel's earlier work and is geared more towards creating a broader rating system to evaluate the overall biological productivity of various cacti/succulents. What I find most useful as of now (having only read it twice) is the observation that the plants will grow rather similarly in a wide variety of nutrient levels as long as the factors of light, heat, and water are addressed first. Pretty basic, I know, but the basics are important. Plus it relieves some of the pressure of trying to fine tune a fert regime.

https://www.jstor.org/stable/2404088

Another by Nobel, this time regarding some Opuntiods. Haven't read it yet but looks promising. Opuntia ficus-indica and it's close relatives are often the subjects of study, I'm guessing because of their relative economic significance, abundance, and relatively fast growth.

- https://acsess.onlinelibrary.wiley.com/ ... 900030030x

I just think the next three are neat and have them in my queue to read. Thought you might enjoy them as well. First is regarding calcium oxalate bioaccumulation and synthesis. Next one is about the endophytic fungi that aid in rock weathering for nutrient absorption by Mammillaria fraileana (incredible stuff tbh, apparently the fungi are even found within the seeds the plant produces so it travels from the parent plant to the offspring) and the other paper is just about M. fraileana and rock types it's found on/near.

- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC148931/
- http://bashanfoundation.com/gmaweb/pdfs ... iaendo.pdf
- https://www.academia.edu/download/48769 ... nizing.pdf

There's actually quite the trove of info to sort through if you type in "Elemental analysis cacti" into Google Scholar.

I also figured the following two charts might be handy to have around and help people like me who are pretty keen visual learners.

Mulder's Chart
Mulder's Chart
Mulder's Chart
Screenshot_20230201-212324_Firefox.jpg (71.72 KiB) Viewed 6226 times
pH Nutrient Availability Chart
pH Chart
pH Chart
20230201_212600.jpg (94.07 KiB) Viewed 6226 times
Obviously the chelated forms of the trace minerals help to mitigate any worry we'd have about pH induced nutrient lockout but it's helpful to see why we aim for the pH we do and why chelated minerals are used in the first place.

The last thing I've got to share is an introductory thread on fertilization that I found very helpful in my early days of growing. It's by an experienced bonsai grower who I hold in high regard. I learned a lot from them before I was comfortable doing my own research and parsing out information found in primary research papers. Obviously deciduous trees and tropical trees differ in many regards compared to cacti/succulents but plants are still plants and I've found quite a lot of value in the thread there.

- https://www.houzz.com/discussions/13894 ... -plants-iv

Hope you find some of this useful or at the least, interesting. Have a good night fellas.
Last edited by SDK1 on Thu Feb 02, 2023 4:40 pm, edited 2 times in total.
5b/6a - Indiana. Half the year growing outdoors, half the year indoors.

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Steve Johnson
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Re: Fertilizers explained (2-part presentation)

Post by Steve Johnson »

Thanks, SDK1. I could never understand chemistry or physics, but I have much more of an aptitude for biology and botany, so I'll dig into your articles when I have the time. (Seems like there's never enough time for all the things we want to do.)

Since Molybdenum doesn't just magically convert NO3 into NH4, curiosity led me to this in the Oxford Academic Annals of Botany article:

https://academic.oup.com/aob/article/96/5/745/180212

The chemistry aspects are over my head, but the article is fascinating nonetheless. Based on my (very) limited current understanding of botany, the conclusion I've reached is that cacti and succulents are just the same as every other plant in some respects. I'm sure that the metabolic processes described in the article apply to cacti and succulents too.

By the way, I see Mulder's chart. Doesn't Scully have a chart too? :lol:
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jerrytheplater
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Re: Fertilizers explained (2-part presentation)

Post by jerrytheplater »

SDK1 wrote: Thu Feb 02, 2023 2:34 am In the meantime I thought I'd share some papers/research/other fert threads I've found useful over the past couple years or that I've been meaning to sit down and read. Having a full time job and 2 kids under 2 means I'm just a bit tired kind of... always.

Park S. Nobel has done a lot of great research over the years with cacti/succulents and a few of their papers aren't paywalled anymore.

The first is one of my earliest finds. I find the tissue analysis tables quite helpful/interesting and I think the values line up rather well with your assessment of 1:0.4:1.1-1.7. (Edit: I generally follow the idea that it's best to supply nutrients in the amount they're being used by the plant and tossue analysis of the plant is how that's derived) I also find the rather strong negative reaction of cacti to Na rather interesting, seems they're more sensitive than leafy plants even. The PDF download is at the bottom of the page.

Hope you find some of this useful or at the least, interesting. Have a good night fellas.
SDK1. Thanks for these article links. I went to the first link by Park S. Nobel which you posted and found the download pdf link at the bottom and went to it. I was still behind a paywall and would need to pay $42.00 to download it. Viewing online for 48 hours was ONLY $10.00. I hate this. Seems to me like this knowledge is being kept hidden from the ignorant masses (like me). Only the high priests of scientific knowledge are allowed to look via their institutional position. Bugs me to no end.
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