Osmocote - opinion required

[Nino_G]

Today I bought a small package (3kg or 6,6lb) of Osmocote Exact 11-11-18+MgO+TE 5-6mnth. It says on the label that it's specially designed for potted plants with high potassium requirements. It was relatively cheap (20€/$) so I decided to buy it and I intend to test it in spring on several plants to see how it works. I've noticed there are some very knowledgeable people on this topic here on forum and I would appreciate your opinion.
Thank you in advance,
Nino

[MikeInOz]

Probably ok to use but I can't understand why manufactures continue to include so much P in their formulations. You just don't need it.
If they are listed, check what the percentage of the P is water soluble - available, citrate soluble - only slowly available, or citrate insoluble - unavailable. Also check if it is for 3, 6 or 9 months. That makes a big difference in how much is released with each watering. If you can take a picture of the label that would be good.
I think I found it...?.... https://icl-growingsolutions.com/orname ... -standard/

That means your actual elmentals are N -11, P- 4.8,- K - 9.3. P is still a bit high for me but go ahead and try it. You can boost the K now and then. Use potassium sulphate in solution. You will probably need to add Ca if your water is very pure (I would do it anyway) Use gypsum. If it has very low Mg you might need to add that as well. Use magnesium sulphate in solution. If you use some soil in the mix you will find it is less of a problem supplying nutrients.

[Nino_G]

Hello Mike,
Thank you for the answer. This particular product is designed for 6 months use (there was no alternatives available, unfortunately. Otherwise I'd buy the one for longer use).
Here is the data sheet:

[Steve Johnson]

A couple of things here. First, this is the guaranteed analysis of the General Hydroponics FloraMicro and FloraBloom liquid fertilizer concentrates I'm using:

FloraMicro-FloraBloom03.jpg (89.8 KiB) Viewed 36317 times

The "derived from" sections are significant because they tell us about the ingredients going into the ferts. "Derived from" labeling is required by state laws in the US. Nino -- if such labeling isn't required outside the US, check your Osmocote's distributor and find out if they can give you the breakdown of ingredients. If they can't...

Osmocote 11_11_18+TE Data Sheet.png (41.46 KiB) Viewed 36317 times

If water soluble P2O5 is the only source of P available to your cacti, this is what we get:

• 8.2% P2O5 x .436 = 3.575% P

• 3.575% P/11% N = 0.325 on the P side of the NPK ratio

That's within the acceptable P range of 0.25-0.35 for cacti and succulents. From Wikipedia (https://en.wikipedia.org/wiki/Phosphorus_pentoxide):

• "P2O5 content is often used by industry as proxy value for all the phosphorus oxides in a material. For example, fertilizer grade phosphoric acid can also contain various related phosphorous compounds which are also of use. All these compounds are described collectively in terms of 'P2O5 content' to allow convenient comparison of the phosphorous content of different products. Despite this, phosphorus pentoxide is not actually present in most samples as it is not stable in aqueous solutions." [My emphasis]

It would be helpful to know the water-insoluble P compounds going into the Osmocote, but you won't get that information unless the distributor provides you with a "derived from" statement. (Question for Mike -- why in the heck would manufacturers use water-insoluble P compounds for their ferts?) What he said here...

You can boost the K now and then. Use potassium sulphate in solution. You will probably need to add Ca if your water is very pure (I would do it anyway) Use gypsum. If it has very low Mg you might need to add that as well.

...is absolutely correct, and if you follow his recommendations, I think you'll do well with the Osmocote you have in mind.

[MikeInOz]

-- why in the heck would manufacturers use water-insoluble P compounds for their ferts?)

I don't know the process so I have no idea. But citrate soluble P is still valuable in the long run especially for in - ground growing so it can be counted a part of the total phosphorus bank in the soil.

[MikeInOz]

Hello Mike,
Thank you for the answer. This particular product is designed for 6 months use (there was no alternatives available, unfortunately. Otherwise I'd buy the one for longer use).
Here is the data sheet:

This product has no sulphur so I would definitely recommend you add gypsum once/year and you will need to water in with magnesium sulphate now and then. Some water supplies have enough Ca, Mg., and S to satisfy plants so you should check, but be careful to make sure the plants get what they need. The rest is good.

[Steve Johnson]

-- why in the heck would manufacturers use water-insoluble P compounds for their ferts?)

I don't know the process so I have no idea. But citrate soluble P is still valuable in the long run especially for in - ground growing so it can be counted a part of the total phosphorus bank in the soil.

Learning something new every day...

This is from the University of Minnesota Extension's website (https://extension.umn.edu/phosphorus-an ... ble-619561):

• "Citrate-soluble: The fertilizer material that isn’t dissolved in water is then placed in an ammonium citrate solution. The amount of P dissolved in this solution is measured and expressed as a percentage of the total in the fertilizer material."

My guess is that the Osmocote Nino has in mind includes ammonium citrate. If I'm correct, then something you said earlier ("citrate soluble - only slowly available") indicates the total amount of P may be a little higher than he might want, but I don't think it would be much of a problem in the long run.

[Nino_G]

Thank you Steve and Mike, you have eased my mind

As for the gypsum, it's not readily available in my area (or in the rest of Europe, as far as I know) in its raw, natural form, but only as processed powder for use in construction. Is that usable in some way?
Also, I don't use tap water (which is very hard), but demineralised RO water.
My substrate mixture contains pumice, lava (scoria), zeolite and akadama. I don't use organic soils. For plants that grow on limestone in nature - most plants in my collection - I add small amount of dolomite chips in the mixture (CaMg(CO3)2) and I also use it for top dressing.

I haven't been adding extra Ca or S so far and plants don't seem to mind. Maybe they're available in the mineral mixture?

[MikeInOz]

Thank you Steve and Mike, you have eased my mind

As for the gypsum, it's not readily available in my area (or in the rest of Europe, as far as I know) in its raw, natural form, but only as processed powder for use in construction. Is that usable in some way?
Also, I don't use tap water (which is very hard), but demineralised RO water.
My substrate mixture contains pumice, lava (scoria), zeolite and akadama. I don't use organic soils. For plants that grow on limestone in nature - most plants in my collection - I add small amount of dolomite chips in the mixture (CaMg(CO3)2) and I also use it for top dressing.

I haven't been adding extra Ca or S so far and plants don't seem to mind. Maybe they're available in the mineral mixture?

Dolomite will contribute Ca and some Mg (depending on the content). If it is hard stone chips, you can add a good amount to the limestone growers.
That will take care of them but you still need Ca and Mg for the non-limestone growers and sulphur for all of them. If you use pure water the S will run out quickly. The processed powder might be ok but test it on something like beetroot seedlings to make sure it has nothing toxic first.

[Steve Johnson]

I'm using a nitrogen-free Cal-Mag made by TPS Nutrients, and the improvements have been pretty amazing since I started using it a couple of years ago. Can we find one in Europe? The answer is -- yes.

Biobizz CalMag is available in Europe and does not contain nitrogen for those who are interested. In an email they wrote: "Biobizz Calmag is a mix of calcium and magnesium stabilized with organic matter instead of nitrogen bases. This organic matter is mainly humic acids, which are always a nice add in any organic grow, as they help with nutrient absorption and transport. All these ingredients are 100% certified as natural, as there isn’t any chemical or artificial substance added to the product." I'm trying to find to find out what the ratio is, but after having asked them 2 times, I think they don't know. Is there a way to test this?

The answer to Oscar's question is also yes:

Biobizz_CalMag_guaranteed_analysis.jpg (167.73 KiB) Viewed 35630 times

Even though we had to get the guaranteed analysis from a US distributor, it'll be the same stuff for customers buying it in Europe. Nino, if you can find it, I think this would be a good supplemental feed for all of your cacti. I've always been bothered by the term "limestone growers" as if cacti ev0lutionarily adapted to growing in native limestone soils can't get their calcium from other sources. This is certainly not the case, and IMO it would simplify matters if you skip on the gypsum and dolomite, and go straight for the Biobizz. Sulfur in the product's magnesium sulfate certainly helps. If you can buy it, the only question I won't be able to answer -- what is the proper dilution? My experience is limited to using liquid fertilizer concentrates, but Mike may have the answer for you.

[Nino_G]

Yes, Biobizz CalMag is readily available here, I just checked. So, you think MgSO₄ will provide enough sulphur?
Here is excerpt from the CalMag data sheet regarding dosage. I guess 0,3ml/liter would be a good starting dose:

[ohugal]

I think the instruction manual mentions to add the product before adding other fertilizers and products. I’m saying this because, if I’m not mistaken, the TPS CalMag is added as the last ingredient of the fertilizer mix. I don’t know if this is important to mention or not.

[MikeInOz]

you think MgSO₄ will provide enough sulphur?

If you are using very pure water and you don't add anything organic to the mix, probably not. Aim for S to be about 1/4 (or more) of the N.

hydroponics.JPG (58.95 KiB) Viewed 34378 times

[Steve Johnson]

Thanks for the information, Oscar! If Nino can't get the Biobizz from a local source, I think he can buy it through Amazon Germany:

https://www.amazon.de/s?k=biobizz+calma ... -doa-p_5_8

...if I’m not mistaken, the TPS CalMag is added as the last ingredient of the fertilizer mix.

That pertains to the General Hydroponics (and in your case Terra Aquatica) fertilizers -- FloraMicro goes in first, FloraBloom goes in last. TPS doesn't say anything about their CalMag one way or the other, but I add it after the FloraBloom. Since Nino would be using an Osmocote slow-release, diluting his water with Biobizz means it'll go in first as Biobizz recommends. Speaking of...

Today I bought a small package (3kg or 6,6lb) of Osmocote Exact 11-11-18+MgO+TE 5-6mnth.

Can you get the 11-11-18 without MgO? Reason I ask is because your cacti will get a good calcium-magnesium balance just with the Biobizz CalMag, but I think they'd get too much Mg if it's in the Osmocote too. By the way -- 18% K2O x .83 = 14.94% K. 14.94%K/11% N = 1.36 on the K side of the ratio, well within the optimal range of 1.1-1.7. You can increase the K with some potassium sulfate in your watering solution, and your cacti could use the additional S.

I haven't been adding extra Ca or S so far and plants don't seem to mind. Maybe they're available in the mineral mixture?

You can't count on your mix for either Ca or S, and this is the reason why I'm recommending the Biobizz CalMag for you -- - a lesson learned from hydrobuilder.com:

• "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]

The quote backs up something Mike said in earlier posts -- there's no such thing as too much Ca, and there's no such thing as Ca toxicity. Dolomite chips for your "limestone growers" certainly help, and regular feeding with dilute Biobizz should make all of your cacti happier in the long run.

you think MgSO₄ will provide enough sulphur?

If you are using very pure water and you don't add anything organic to the mix, probably not. Aim for S to be about 1/4 (or more) of the N.

A good argument in favor of what I just said about potassium sulfate to supplement Nino's Osmocote 11-11-18. Now, here's where I would have some difficulty -- doing a sort of "mix 'n match" between the slow-release fert and fast release of supplemental nutrients in the watering solution. If we knew the parts-per-million amount of N and K being released with each watering, we could figure out the right dilution rate for the potassium sulfate going into Nino's watering solution. Mike, do you have an educated guess on this?

[Nino_G]

Thank you all for reliable (and confusing ) answers.

Steve, I think you might have missed my last post - I have located local source of Biobizz CalMag and already ordered 500ml bottle. I would like to know what dosage do you apply for your plants (i added manufacturer's recommendations table in my last post).

you think MgSO₄ will provide enough sulphur?

If you are using very pure water and you don't add anything organic to the mix, probably not. Aim for S to be about 1/4 (or more) of the N.

Mike, what would you suggest as an adequate source of sulfur? Would addition of small amount of peat to the (otherwise 100% inorganic) substrate mixture help with the issue? What other organic materials are good sources of sulfur?
Also, since most species of cacti in my collection grow in the wild on pure rock (other than gypsum) with very little to none organic materials, and are watered by rain (and demineralized water is closest thing to the rainwater in terms of properties), how do they get adequate sulphur in nature?

Now, here's where I would have some difficulty -- doing a sort of "mix 'n match" between the slow-release fert and fast release of supplemental nutrients in the watering solution. If we knew the parts-per-million amount of N and K being released with each watering, we could figure out the right dilution rate for the potassium sulfate going into Nino's watering solution. Mike, do you have an educated guess on this?

Here's another variable that makes equation even more difficult to solve: Manufacturer of Osmocote claims that each individual pellet of fertilizer is covered in polymer membrane and permeability of the membrane changes according to the temperature - the warmer it gets, the more of the nutrients it releases.

I plan to use CalMag from now on on all plants in addition to the regular liquid fertilizer feeds, and I'll start experimenting with Osmocot/CalMag combo in the spring on small number of plants and see the results. According to the manufacturer of Osmocote, if stored correctly, it has indefinite shelf life, so I'm in no hurry .