Osmocote - opinion required

[Steve Johnson]

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).

"Senior moment" -- I saw your post, but I thought it was from Oscar. Sorry about that. For the CalMag I get from TPS Nutrients, I dilute 1/4 teaspoon per gallon of my watering solution. That works out to be 0.326 mL/L. 0.3 mL/L should be a good, steady dosage for you.

[Steve Johnson]

Thank you all for reliable (and confusing ) answers.

If you want more confusion, try this:

https://mrec.ifas.ufl.edu/Foliage/Resrpts/rh_90_15.htm

When I read through that article, here are the take-aways I got from it:

• The Osmocote slow-release fertilizers have better release rates when plants are under shade or in a greenhouse than they do under full sun. By that we mean -- nutrients are released for uptake by the roots. Poor release rates under full sun mean that nutrients aren't being taken up by the roots as much as they should.

• As you noted, Osmocote's release rates vary with temperature. Fine for growers who live where the spring/summer growing season is consistently hot, but I have to wonder if your cacti will be getting the most "bang for the buck" nutrient-wise in Zagreb.

The more I think about it, the less thrilled I am with the idea that you should try the Osmocote you have in mind. For one thing, I wouldn't use any fertilizers without S. For another, your cacti need a steady, reliable supply of nutrients throughout the entire growing season -- IMO Osmocote isn't the best because your climate won't be hot enough to make the most of it in spring.

[Nino_G]

If you want more confusion, try this:

Most of all, I'm confused how did I manage growing cacti so far. Here are the facts:

- I've been growing cacti for more than 30 years (still have several Aztekiums, Strombocactus and Turbinicarpus in collection that are over 33 years old)
- For most of that time I've been using simple substrates that consisted of silica gravel/sand, crushed bricks and some peat and limestone or dolomite chips added for plants that are found on limestone in habitat.
- For the last 6 years I've been using 100% mineral substrates (pumice, scoria, zeolite, akadama)
- I've always been using commercial store-bought fertilizers for cacti without giving them much thought, except that they don't contain to much N
- Lately I've been using liquid fertilizer from German cacti nursery (Uhlig Kakteen) diluted to 1/5 of recommended dosage
. None of the above mentioned fertilizers (as far as I can remember) had sulphur (or calcium) specified as ingredient
- I never used tap water for watering, but rainwater, distilled water, and last several years demineralized water
- All of my plants are compact, healthy, overwinter without problem, flower in abundance and produce viable seed.

How to explain that?

UPDATE:

I just find an article on sulfur deficiencies that says this:

"A less obvious sulfur source for plants is from the atmosphere. Burning fuels releases sulfur dioxide, which plants take into their tissues during respiration. Plants vary widely in tolerance to sulfur dioxide because of the differences in the efficiency with which they absorb the gas and the plant’s ability to detoxify the pollutant and dispose of excess sulfur. Much sulfur absorbed by leaves is translocated to other plant parts, thus diluting it."

Since all of my plants are kept outside on the balcony, and I live in the urban area with plenty of traffic, could this be answer to my question?

[Steve Johnson]

I just find an article on sulfur deficiencies that says this:

"A less obvious sulfur source for plants is from the atmosphere. Burning fuels releases sulfur dioxide, which plants take into their tissues during respiration. Plants vary widely in tolerance to sulfur dioxide because of the differences in the efficiency with which they absorb the gas and the plant’s ability to detoxify the pollutant and dispose of excess sulfur. Much sulfur absorbed by leaves is translocated to other plant parts, thus diluting it."

Since all of my plants are kept outside on the balcony, and I live in the urban area with plenty of traffic, could this be answer to my question?

Quite possibly. And what we're talking about isn't just vehicle traffic, it could also be industry (as in factories, power plants, etc.). Check out the air quality in Zagreb:

https://www.iqair.com/croatia/zagreb

If your cacti are taking up enough S from sulfur dioxide in the air, it would explain why you really don't need S in a fertilizer. This brings up another factor to consider -- from Wikipedia:

• "In atmospheric chemistry, NOx is shorthand for nitric oxide (NO) and nitrogen dioxide (NO2), the nitrogen oxides that are most relevant for air pollution."

Is it possible that your cacti are getting N from the polluted air? If so, it'll be nitrate and nitrite N in your rainwater.

If you want more confusion, try this:

Most of all, I'm confused how did I manage growing cacti so far. Here are the facts:

- I've been growing cacti for more than 30 years (still have several Aztekiums, Strombocactus and Turbinicarpus in collection that are over 33 years old)
- For most of that time I've been using simple substrates that consisted of silica gravel/sand, crushed bricks and some peat and limestone or dolomite chips added for plants that are found on limestone in habitat.
- For the last 6 years I've been using 100% mineral substrates (pumice, scoria, zeolite, akadama)
- I've always been using commercial store-bought fertilizers for cacti without giving them much thought, except that they don't contain to much N
- Lately I've been using liquid fertilizer from German cacti nursery (Uhlig Kakteen) diluted to 1/5 of recommended dosage
. None of the above mentioned fertilizers (as far as I can remember) had sulphur (or calcium) specified as ingredient
- I never used tap water for watering, but rainwater, distilled water, and last several years demineralized water
- All of my plants are compact, healthy, overwinter without problem, flower in abundance and produce viable seed.

How to explain that?

Your approach to growing cacti is what we know as the "hard" style -- mimicking (or at least trying to mimic) what they would look like in the wild. Obviously you've done well with that approach for more than 30 years, so I'm not sure why you'd want to change your growing practice by experimenting with the Osmocote 11-11-18 slow release. Are your plants calcium-deficient? Obviously not, otherwise they wouldn't be looking so good (and you'd know it). Actually, there is a reason why you might want to change...

I learned a lot about fertilizers and how various nutrients function in cacti from MikeInOz. If you haven't seen it before, go here...

https://www.cactiguide.com/forum/viewtopic.php?t=47603

...and while you're at it, read the follow-up posts from Mike and SDK1 for some of the science behind what I've been doing over the last couple of years. If you don't want to go through everything (and yes, it's complicated), I'll say this is simply as I can:

• With the right NPK balance and the right dosages of all nutrients (N, P, K, Ca, Mg, and S being the most significant), cacti under cultivation are able to achieve the kind of genetic growth potential that is impossible with their counterparts fending for themselves in the wild.

Using nitrogen as a benchmark, I've found that N in the range of 40-75 parts-per-million with each feeding is quite appropriate to 100% mineral substrates like the 60% pumice-40% granite gravel mix I use for almost all of my cacti. If N is more in the range of 20-25 ppm per feeding, this would be consistent with the "hard" growing style. Anything much above 90 ppm N per feeding, and growers end up with bloated-looking cacti being pushed beyond their genetic growth limits.

There's really no "right" way to grow cacti, so this is simply a matter of the grower's individual preference. I'm not sure if you'd want to change anything after 30-plus years of successfully growing so many cacti in the "hard" style. However, if you're up for some experimentation, I'll recommend that you A. avoid the Osmocote slow-release because it introduces too many variables you can't account for, and B. give me the guaranteed analysis of what's in the Uhlig Kakteen liquid fertilizer. From there I can determine if this would be worth pursuing on your end.

[MikeInOz]

Nino_G post_id=404986 time=1705132927 user_id=19124]


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?

It is very unlikely that cacti in the wild row on ''pure rock'' Many of the species you would possibly assume do (like the one in your avatar) grow amongst rocks in the ground.... https://www.inaturalist.org/observation ... _id=206027
https://www.inaturalist.org/observation ... _id=206027 The ones that do grow on rock (such as Mamm plumosa - https://www.inaturalist.org/observation ... _id=206483 ) grow in cracks that would have had clay dust and other materials washed or blown into those cracks in the rock over the centuries. So they get their sulphur from the same sources -gypsum mainly and some from decomposed organic material. How do we supply sulpher (as sulphates)? From fertilizers and or gypsum and/or organic materials and/or soil if there is not enough in the irrigation water or even the air in polluted places) I'm not sure if akadama has much S in it??
So you either need to switch to another osmocote formulation, or find a source of S in some other way. Maybe you can order some pure calcium sulphate from your local chemist or gypsum from an agricultural supplier or a nursery (it is often used as a clay breaker) Peat is not a good source as far as I know. It is too old (leached) Even something like cow manure - which is a good source - will run out sooner or later. Because sulphate is a negatively charged anion (like phosphate and nitrate) it is readily leached from pots so it has to be constantly supplied. But that doesn't mean you need a lot, just a steady supply. One good thing is that we don't water cacti much so the leaching will be much less than things we water everyday.

[MikeInOz]

If you want more confusion, try this:

Most of all, I'm confused how did I manage growing cacti so far. Here are the facts:

- I've been growing cacti for more than 30 years (still have several Aztekiums, Strombocactus and Turbinicarpus in collection that are over 33 years old)
- For most of that time I've been using simple substrates that consisted of silica gravel/sand, crushed bricks and some peat and limestone or dolomite chips added for plants that are found on limestone in habitat.
- For the last 6 years I've been using 100% mineral substrates (pumice, scoria, zeolite, akadama)
- I've always been using commercial store-bought fertilizers for cacti without giving them much thought, except that they don't contain to much N
- Lately I've been using liquid fertilizer from German cacti nursery (Uhlig Kakteen) diluted to 1/5 of recommended dosage
. None of the above mentioned fertilizers (as far as I can remember) had sulphur (or calcium) specified as ingredient
- I never used tap water for watering, but rainwater, distilled water, and last several years demineralized water
- All of my plants are compact, healthy, overwinter without problem, flower in abundance and produce viable seed.

How to explain that?

UPDATE:

I just find an article on sulfur deficiencies that says this:

"A less obvious sulfur source for plants is from the atmosphere. Burning fuels releases sulfur dioxide, which plants take into their tissues during respiration. Plants vary widely in tolerance to sulfur dioxide because of the differences in the efficiency with which they absorb the gas and the plant’s ability to detoxify the pollutant and dispose of excess sulfur. Much sulfur absorbed by leaves is translocated to other plant parts, thus diluting it."

Since all of my plants are kept outside on the balcony, and I live in the urban area with plenty of traffic, could this be answer to my question?

Yes it is possible your air contains some S, and even your collected rainwater if you live in a big city. Any S in the scoria, pumice, zeolite and akadama will not last long. The liquid fertilizer from Germany may also contain it.
I live in a rural area and we have some of the most pure water in the world so there is neither enough S, Ca, or Mg in our water and none in the air.

[MikeInOz]

The more I think about it, the less thrilled I am with the idea that you should try the Osmocote you have in mind. For one thing, I wouldn't use any fertilizers without S. For another, your cacti need a steady, reliable supply of nutrients throughout the entire growing season -- IMO Osmocote isn't the best because your climate won't be hot enough to make the most of it in spring.

As long as there is some moisture, osmocote works by releasing more as the temp increases. So, for example, you might get 50% released at 25 degrees C over say 6 months. Therefore, all to you need to do is increase or decrease the added rate according to the temperatures you experience. When it's cold you won't get much if any released but you don't want it then anyway.

[Steve Johnson]

From Wikipedia, this is the climate data for Zagreb:

Zagreb_climate_data.jpg (100.71 KiB) Viewed 5815 times

Looking at the mean daily maximum ranges April-September, the Osmocote 11-11-18 seems to be awfully unreliable for delivering a steady supply of nutrients to Nino's cacti. Then again, it may be fine if he uses it to supplement a liquid fertilizer.

[MikeInOz]

From Wikipedia, this is the climate data for Zagreb:

Zagreb_climate_data.jpg

Looking at the mean daily maximum ranges April-September, the Osmocote 11-11-18 seems to be awfully unreliable for delivering a steady supply of nutrients to Nino's cacti. Then again, it may be fine if he uses it to supplement a liquid fertilizer.

From my book... ''Nomimal release times for osmocote is 21C.''
Osmocote 9 month at a constant 21C has 52% remaining after 19 weeks (4.5 months, which is the growing season) So a 6 month formulation will probably have about 35% left more or less) That is a constant temp but does not take into account day/night or higher temps during summer. But it gives you a rough idea. Osmocote is usually a blend so you get some very quick release and some very slow and some in between. I find about 2/3 of the prills completely empty after a year and some with about 20 or 30% left. (My osmocote is a ''6 month''.) That's the time to add more. My temps are a little warmer (the growing season June, July, Aug, Sept) than in your chart but not much. So, if Nino adds a tiny amount more than I do he will get the same results as I do (all other things being equal) I add about 1 teaspoon to a 80mm pot when I pot up or once/year.

[Nino_G]

Thank you Steve and Mike once again for your effort in answering my questions. Many things are much more clear in my mind now.
As I said before, I have enough seedlings to experiment with (majority will remain in regular growing schedule and of the rest I will form test groups on which I will test the Osmocote - that way I will have something to compare the results with). I plan to begin using CalMag for all of the plants in combination with usual fertilizer.

P.S. Mike, I managed to find pure calcium-sulfate (gypsum) that is sold as food additive (apparently used in the process of brewing beer). It comes in powdered form. Could you please suggest what is the best way to implement it?

[MikeInOz]

P.S. Mike, I managed to find pure calcium-sulfate (gypsum) that is sold as food additive (apparently used in the process of brewing beer). It comes in powdered form. Could you please suggest what is the best way to implement it?

Calcium sulphate a a solubility of 2.4 grams per litre of water. So you could add it at say 0.1 grams/Lt and use that with each watering or twice as much with every second watering or you can sprinkle 0.5-1 grams on the pot (50 -100mm diameter) surface. The length of time it will last depends on the size of the particles. For example, if they are the size of sugar grains, it should last the entire growing season. If they are much finer, you might have to apply twice. Put some in water and see how long it takes to dissolve to help you decide. In general we water our cacti about 10 to 15 times a year I would guess.
** As an experiment, try dissolving a few teaspoons in some water in summer and let it dry our again. You might find you are left with much larger crystals which you can use.

[Steve Johnson]

Mike -- thanks for the info on Osmocote release rates based on temperature.

Nino -- I'm curious about the Uhlig Kakteen fertilizer you've been using recently, so please post its guaranteed analysis. Here's the reason why I mention it...

I started using Dyna-Gro All-Pro 7-7-7 back in 2012. That's 7% P2O5, so the actual percentage was 3.052% P. 3.052%P/7% N = 0.436 on the P side of the ratio -- too high. It took about 6 or 7 years before I saw reduced flowering in cacti that had been flowering well before then. When Dyna-Gro discontinued the 7-7-7, I switched over to the General Hydroponics FloraMicro 5-0-1 and 0-5-4 FloraBloom ferts last spring. Same problem with the P being too high in relation to N, so I corrected the imbalance with an ammonium sulfate-potassium sulfate stock solution I add to my watering solution. With lower P and higher K, the growing improvements were marvelous -- I'll show you some examples starting here:

https://www.cactiguide.com/forum/viewto ... 52#p401552

I wanted to give you a "heads up" on this in case the Uhlig Kakteen's P is too high. If it is, you may want to rethink whether you should continue using it.

[Nino_G]

Nino -- I'm curious about the Uhlig Kakteen fertilizer you've been using recently, so please post its guaranteed analysis. Here's the reason why I mention it...

Here is the excerpt from the Uhlig web-page:

It appears to be low on potassium.

[Nino_G]

Calcium sulphate a a solubility of 2.4 grams per litre of water. So you could add it at say 0.1 grams/Lt and use that with each watering or twice as much with every second watering or you can sprinkle 0.5-1 grams on the pot (50 -100mm diameter) surface. The length of time it will last depends on the size of the particles. For example, if they are the size of sugar grains, it should last the entire growing season. If they are much finer, you might have to apply twice. Put some in water and see how long it takes to dissolve to help you decide. In general we water our cacti about 10 to 15 times a year I would guess.
** As an experiment, try dissolving a few teaspoons in some water in summer and let it dry our again. You might find you are left with much larger crystals which you can use.

Thanks Mike,
I also have an idea to mix some of the powder with water into a thick paste (as you would to plaster walls) and let it set/dry. Then I could crush it into chips and mix it in the substrate. It seems to me that would be long-lasting solution. Do you think that would work?
Regards,
Nino

[MikeInOz]

Thanks Mike,
I also have an idea to mix some of the powder with water into a thick paste (as you would to plaster walls) and let it set/dry. Then I could crush it into chips and mix it in the substrate. It seems to me that would be long-lasting solution. Do you think that would work?
Regards,
Nino

There is only one way to find out....