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

[Steve Johnson]

As always, great discussion on this thread.

Mike and Steve, do either of you guys have any thoughts on whether this fertilizer regimen would be ok for agaves or ocotillo? If not, how should it be modified?

Aside from my presentation that started it all, this thread has turned out to be a gold mine of information -- go to page 1 and read through the exchanges between Mike and SDK1. You'll come to find out that all plants have basically the same nutrient requirements, and it really surprised me to know how much xeric and nonxeric plants have in common regarding their optimal N, P, and K ranges. Long story short, the new fert regimen I'm following will work well for cacti, succulents, and any other ornamental plants you're growing.

Even for roses? Yes -- you rose growers out there may find this rather enlightening:

https://www.rose.org/single-post/phosph ... good-thing

And finally, confirmation from Mike:

The same for everything. Just remember that many agaves grow on limestone so you might make allowances for that but even if you don't I suspect everything will be fine.

There's a lot of horticultural science out there, and many growers are simply unaware of it. We're getting a taste of it here -- for those of you who are interested (and a good dose of curiosity helps!), you'll find the whole thing to be fascinating.

[jerrytheplater]

Even for roses? Yes -- you rose growers out there may find this rather enlightening:

https://www.rose.org/single-post/phosph ... good-thing

Good article Steve. I copied a very interesting paragraph and added in two edits for my own use.

Another question to consider is the amount of phosphorus a rose plant can use. Analysis of plant tissues indicate that the amount of phosphorus in those tissues is around 1/6 of the amount of nitrogen and 1/4 that of potassium. (edit Jerry Smith 9-1-2023: 6-1-4 elemental, & 6-2.3-4.8 or 3-1.2-2.4 N-P2O5-K2O) In other words, of the three, phosphorus exists in the smallest amounts, leading one to wonder how much extra phosphorus the plant needs. Research linking increased phosphorus levels to increased blooming is scarce, while there is sound research that demonstrates that even small amounts of phosphorus are needed for bloom. Commercial growers of roses for cut-flower production typically use fertilizers with a 3-1-2 NPK (edit Jerry Smith 9-1-2023: N-P2O5-K2O) ratio. Roses are not the only crop where this has been explored. There is no plant that uses more phosphorus than nitrogen and potassium.

[Steve Johnson]

I found an article on hydrobuilder.com (https://hydrobuilder.com/learn/npk-rati ... t-balance/) which explains this rather well. There's only one limitation -- the article applies to hydroponic crop production, not growing ornamental plants like cacti and succulents. As we go through the following quotes, I'll comment on each one, pointing out things that are specific to cacti and succulents:

• "Nitrogen is responsible for producing robust, leafy growth. This is why you’ll see it in higher ratios during veg, and it will fall off during flower."

Not true for ornamentals -- N is used with the same ratio all the time. Also, N promotes stem growth in cacti and leaf growth in succulents.

• "Phosphorus does the opposite, helping your plants develop flowering sites and produce large buds. Traditionally, growers would ramp up the phosphorus during flower because of this."

Actually, not the best explanation because it applies only to crops, so here's a better one from The Spruce (https://www.thespruce.com/):

• "Phosphorus plays a key role in the growth of roots, blooming, and fruiting, which is why it is an essential nutrient for your plants in spring. Phosphorus contributes to many fundamental plant processes, such as rooting and seed formation."

Not just in spring -- P is essential for cacti and succulents throughout the entire growing season. Now back to Hydrobuilder:

• "Potassium, on the other hand, isn’t necessarily veg or bloom specific. Instead, it helps regulate a variety of plant functions, including strong root growth, increased resistance to disease and increased water intake, along with thick, sturdy growth."

Definitely true for all plants.

• "Magnesium and calcium go hand in hand, and are often an area where plants become deficient. Magnesium helps aid in the uptake and utilization of other nutrients, along with producing carbs and sugars to help during flower."

Once again, definitely true for all plants.

• "Calcium has a similar role in plants as in humans, helping produce strong cells and root walls. This leads to stronger plants. We've recently come to understand that calcium is actually the dominant nutrient in most plants." [My emphasis]

Quite a revelation, and it backs up a couple of things MikeInOz has said in previous posts -- "there's no such thing as too much Ca" and "there's no such thing as Ca toxicity". In fact, I offer the possibility that Ca higher than N could be a very good thing at least for cacti and succulents.

• "Sulfur helps produce chlorophyll, and plays an essential role in foliage and root development."

Applies to cacti and succulents too. Sulfur deficiency = chlorosis, and yellowing of the skin indicates a serious S deficiency. If you have a good amount of sulfate in your watering solution, chlorosis won't be a problem.

This brings us to...

Mulders_chart.jpg (87.83 KiB) Viewed 4064 times

• "This shows how nutrients interact with one another. Nutrients interact either antagonistically or synergistically.
  
  They can increase the uptake of one another. Or, they will fight among each other and can lock each other out if the balance/ratio is off."

Precisely why NPK ratios are key to knowing if your fertilizer is right or wrong for cacti and succulents. The ideal NPK ratio = 1:0.25-0.35:1.1-1.7. Simply put -- of the 3 primary major nutrients, ornamentals need the least amount of P. If your feeding regimen has the ideal ratio, all other nutrients are there in sufficient amounts, and you don't overdo it on the fertilizer (plus any supplements you may need), your plants will be happy, healthy and growing well over the years. (Many thanks to SDK1 for posting Mulder's Chart on 2/1/2023.)

[AirWreck]

I haven't finished reading this thread but wanted to throw this out there whilst I'm thinking about it. This is a trace mineral fertilizer that I've long used for all my cacti and gardening endeavors: Planters II
https://fertilizerbrokerage.com/wp-cont ... ations.pdf
"Derived from metamorphosed evaporite". Meaning its the evaporated remains of an ancient riverbed. As such, its rated for organic agricultural. its said to contain up to 30 trace minerals.

How good is it for cacti? I cannot say but its been in use for agriculture since the 1970s. This webpage says it can be used for xeric plants:
https://www.highcountrygardens.com/prod ... lizer-5-lb

its hard to find recommended application for potted plants but what I've found is 1tsp:6inch pot.
Something to consider.

[jerrytheplater]

I haven't finished reading this thread but wanted to throw this out there whilst I'm thinking about it. This is a trace mineral fertilizer that I've long used for all my cacti and gardening endeavors: Planters II
https://fertilizerbrokerage.com/wp-cont ... ations.pdf
"Derived from metamorphosed evaporite". Meaning its the evaporated remains of an ancient riverbed. As such, its rated for organic agricultural. its said to contain up to 30 trace minerals.

How good is it for cacti? I cannot say but its been in use for agriculture since the 1970s. This webpage says it can be used for xeric plants:
https://www.highcountrygardens.com/prod ... lizer-5-lb

its hard to find recommended application for potted plants but what I've found is 1tsp:6inch pot.
Something to consider.

I saw that 20% is soluble right away, so adding it to your pot should work out fine. When you water, a little will dissolve each time. Greensand is another trace mineral product naturally mined. It has a marine origin.

[hoopgod32]

• "Magnesium and calcium go hand in hand, and are often an area where plants become deficient. Magnesium helps aid in the uptake and utilization of other nutrients, along with producing carbs and sugars to help during flower."

Once again, definitely true for all plants.

• "Calcium has a similar role in plants as in humans, helping produce strong cells and root walls. This leads to stronger plants. We've recently come to understand that calcium is actually the dominant nutrient in most plants." [My emphasis]

Quite a revelation, and it backs up a couple of things MikeInOz has said in previous posts -- "there's no such thing as too much Ca" and "there's no such thing as Ca toxicity". In fact, I offer the possibility that Ca higher than N could be a very good thing at least for cacti and succulents.

Mulders_chart.jpg

Love this chart! Very helpful to see how everything works together and understand just how important proper balance is for plant health. Should be bookmarked for all hobbyist growers.

Per our last convo on a different thread about calcium binding, I did learn recently (thanks to a chemist friend) that calcium does indeed bind with phosphate. Calcium acetate (acidifying with vinegar) is the most effective at this due to its high solubility. The key to preventing this, as shown in the chart you shared, is to have the proper balance between cal:mag (synergistic nutrient) which is around 4:1 along with a roughly equal nitrogen:calcium. This explains why many fertilizers with high phosphorous content do not contain calcium -- they will precipitate at high levels in a single solution.

With that said, isn't excessive calcium that is out of balance with other nutrients actually detrimental for plant health? As shown in the chart, calcium can form antagonistic relationships with many other nutrients if it's in excess thereby preventing their uptake. This competes directly with the concept that "there's no such thing as too much Ca." It's possible Mike's statements are missing additional context, but I have to definitely push back on the notion that excess calcium has no negative impact.

Good excerpt from this article University of Michigan's Agriculture unit:

"If calcium is in excess it can simply out-compete other elements such as potassium and magnesium for uptake sites on the roots, or it can change soil chemistry by elevating pH to the point iron and boron become unavailable."

[Steve Johnson]

Man, this is complicated...

Per our last convo on a different thread about calcium binding, I did learn recently (thanks to a chemist friend) that calcium does indeed bind with phosphate. Calcium acetate (acidifying with vinegar) is the most effective at this due to its high solubility. The key to preventing this, as shown in the chart you shared, is to have the proper balance between cal:mag (synergistic nutrient) which is around 4:1 along with a roughly equal nitrogen:calcium.

We'll go through a few numbers. First -- when I dilute 1/2 tsp. of my General Hydroponics FloraMicro 5-0-1 per gallon of water, I get 33 ppm Ca and 10 ppm Mg. 1/4 tsp. nitrogen-free TPS CalMag adds another 15 ppm Ca and 4 ppm Mg for a total of 48 ppm Ca and 14 ppm Mg in the watering solution. Ca-Mg ratio is 3.4-1. I'm also adding an ammonium sulfate-potassium sulfate stock solution to the watering solution. Total N in the watering solution is -- 48 ppm. The only variable I can't account for are the amounts of Ca and Mg in my acidified water. All I can tell you is that my tap water is reading about 100 ppm carbonate per the MedLab Diagnostics test strips I'm using. Assuming that it's all CaCO3, we're talking about 40 ppm Ca. According to Vernier Science Education (https://www.vernier.com/experiment/wqv- ... -hardness/):

• "On average, magnesium hardness represents about 1/3 of total hardness and calcium hardness about 2/3."

This is a general statement, and I do realize that whether it applies or not will depend on local geology and water sources. Taking a water sample to my local test lab costs a few hundred bucks, and I can't justify the expense (I am just a hobbyist, after all), so we'll have to leave the amounts of Ca and Mg in my tap water as an unknown variable. The question for you is (and going by your best guess) -- am I fine with white vinegar or should I change to citric acid as my acidifier? Interesting side note by the way:

• TPS CalMag is derived from calcium carbonate and calcium magnesium carbonate. It includes -- citric acid.

With that said, isn't excessive calcium that is out of balance with other nutrients actually detrimental for plant health? As shown in the chart, calcium can form antagonistic relationships with many other nutrients if it's in excess thereby preventing their uptake. This competes directly with the concept that "there's no such thing as too much Ca." It's possible Mike's statements are missing additional context, but I have to definitely push back on the notion that excess calcium has no negative impact.

I brought the matter up with Mike via PM, so let's see if he responds here. In the meantime, I'll tell you that growing improvements in my cacti have been substantial ever since I started using a well-balanced fertilizer regimen with the TPS CalMag supplement plus the Ca (and Mg if it's there) in my acidified tap water last year. Yeah, I know -- anecdotal evidence, so take it for whatever it's worth.

Good excerpt from this article University of Michigan's Agriculture unit:

"If calcium is in excess it can simply out-compete other elements such as potassium and magnesium for uptake sites on the roots, or it can change soil chemistry by elevating pH to the point iron and boron become unavailable."

I'd be hesitant to extrapolate agricultural research and apply it to cacti being grown under pot cultivation. Also, the article you linked to assumes the presence of soil -- IMO doesn't apply to those of us growing cacti in a soilless mineral mix.