On the question of limestone growers...

[abhikjha]

Hi Mike, I have a liquid fertilizer with NPK of 7 6 11 with micronutrients where Ca / Mg ratio is around 3. My tap water ph is around 7 to 8 which I acidify to bring it to 5.5. Do you think if I add this liquid fertilizer, it will do good for my plants?

[MikeInOz]

Hi Mike, I have a liquid fertilizer with NPK of 7 6 11 with micronutrients where Ca / Mg ratio is around 3. My tap water ph is around 7 to 8 which I acidify to bring it to 5.5. Do you think if I add this liquid fertilizer, it will do good for my plants?

Yes probably, but personally I would aim for a higher Ca/Mg ratio by adding crushed rock gypsum to the top of the mix. But I think it will be fine. If there is no solid Ca in the mix, maybe keep the final pH of the solution around 6.

[abhikjha]

Thanks Mike. It's really helpful. Can crushed gypsum be replaced by bonemeal as top dressing? If yes, what should be the Ph value to aim for?

[DaveW]

I would not use bonemeal as a top dressing since it may go mouldy. If you do put it on the soil it needs working into the soil top surface with say a small fork and then top dress with grit or similar on the top of that. Obviously if you use bone meal it is best mixed in with the potting soil.

[abhikjha]

Thanks a lot Dave. Yeah it can go mouldy and in my humid condition, fungus will have feast on it. I will avoid it. As Mike said earlier, will go with Ca/mg as 3 with my current fertilizer and observe how they react to it.

[abhikjha]

Hi Mike, one residual question on NPK. I read that you suggest to use NPK of 1:0.4:1.5 while my NPK will be 1:0.85:1.6. Should I be worried about using this? What would be the harm in case P is higher? Also, what's the benefit of adding potassium sulphate once in a while?

[Steve Johnson]

See this:

https://www.gardenmyths.com/fertilizer- ... ally-mean/

Check your fertilizer's label and see if it indicates elemental values for P and K. If it indicates only P2O5 and K2O, the %P on the label x .436 gives you the % of elemental P, and the %K on the label x .83 gives you the % of elemental K. Should that be the case, your actual NPK is 7-2.6-9, giving you a ratio of 1:0.4:1.3. The balance between N and P is good, a tad lower than the ideal for K, although I don't know if it would be significant enough to worry about.

[abhikjha]

Thanks Steve! Actually my fertilizer will be a mix of these three hydroponics fertilizer recently launched by one of the biggest agri companies in India. I spoke with the company on Amazon and they said these three should be mixed (1ml in 1litre of each one, so 3ml in 3 litres).
Here are the photos of their constituents:

Can you please let me know what to make of it?

[abhikjha]

Aah I got it. After reading through the link you shared, the calculation makes sense! Basically P and K is recalculated as P x 0.436 and K x 0.83. I can now be worry free and use this . Thanks again! Also what's the role of potassium sulphate? How often do we need to use it?

[Steve Johnson]

Aah I got it. After reading through the link you shared, the calculation makes sense! Basically P and K is recalculated as P x 0.436 and K x 0.83. I can now be worry free and use this ??. Thanks again! Also what's the role of potassium sulphate? How often do we need to use it?

Just went through the labels of the fertilizers you posted, and we'll go through it...

The NPK total for all 3 ferts is 7-6-11. Using the P and K calculations I gave you (so glad I was able to pass that bit of info on! ), the elemental NPK values are actually 7-2.6-9.1. Using N as a constant of 1, the ratio works out to be 1:0.4:1.3. The balance between N and P is good, so supplementing with Potassium sulfate is designed to bring the K side of the ratio up from 1.3 to 1.5. I'm using 0-0-52 Potassium sulfate, and you might see that, although 0-0-50 is probably the standard you'll find -- IMO the difference between 50 and 52 is insignificant. There are, however, a couple of downsides:

• From what I've seen on Amazon, we can get it only by the pound (US) or kilogram everywhere else in the world. Great if you have a massive collection or you own a nursery, not so great if your collection is on the small side (like mine -- I have only 68 cacti, and the biggest one by far is a 15" tall Cephalocereus senilis). 100 grams would last you quite a long time, and your challenge will be to find it in that small of a quantity. What saved me here was being able to buy a 3.5-ounce packet of the 0-0-52 on eBay.

• If you get that far, unfortunately my very limited math skills will fail the both of us -- I haven't a clue about how much Potassium sulfate should go in with your ferts. Potassium sulfate contains 44% Potassium, so all I can tell you is that the elemental K value of 0-0-50 is actually 0-0-22. If you can figure out the math to determine the amount you need, then blessings upon you!

My Dyna Gro 7-7-7 contains only a trace amount of Sulfur, so the Potassium sulfate addresses an S deficiency I didn't even konw I had until Mike informed us about its importance as a minor nutrient for cacti. You'll already have 1% combined S (don't know what "combined" means) in the 0-5-4 fert, so I'm not sure if the additional S in a Potassium sulfate supplement would be a problem. If he says that you'll be fine with the 3 ferts you have in mind, you can skip on the supplementation. I'm concerned about the fact that you have 5% Calcium in the 5-0-1 and total Magnesium of 1.5% in the other 2 ferts. That works out as a Ca-to-Mg ratio of 2.5:1, but the "ideal" ratio should be 4:1. You can bring the Calcium side of the ratio up, but we'll have to defer to Mike on suggesting your best course(s) of action. I sincerely wish I could help you more, but this is as far as I can go. By the way, I really like the micronutrients in the 5-0-1.

[abhikjha]

Thanks Steve for this detailed overview! As usual it's very helpful. I will defer the use of potassium sulphate as of now, don't want to overdose the plants without knowing the full impact.

On Ca to Mg ratio, I guess it's 5% Ca in 5 0 1 and (1.5% Mg in 0 5 4 and 0.5% Mg in 2 1 6, total 1.55% Mg). If I divide 5% by 1.55%, the ratio is 3.22. Can you please tell me how did you get 2.5:1. I know it's not idea 4:1 but 3.22 is nearly there, so in my view should be fine as Mike suggested earlier.

[Steve Johnson]

On Ca to Mg ratio, I guess it's 5% Ca in 5 0 1 and (1.5% Mg in 0 5 4 and 0.5% Mg in 2 1 6, total 1.55% Mg). If I divide 5% by 1.55%, the ratio is 3.22. Can you please tell me how did you get 2.5:1. I know it's not idea 4:1 but 3.22 is nearly there, so in my view should be fine as Mike suggested earlier.

You and I both made a boo-boo. Mg in the 2-1-6 is .05%, not 0.5%, but you have the total right at 1.55%. You also have the ratio right as 3.22:1 -- unless Mike says otherwise, that's close enough. I honestly don't know how I could've come up with 2.5. I seriously hate making mistakes like that.

[MikeInOz]

Hi Mike, one residual question on NPK. I read that you suggest to use NPK of 1:0.4:1.5 while my NPK will be 1:0.85:1.6. Should I be worried about using this? What would be the harm in case P is higher? Also, what's the benefit of adding potassium sulphate once in a while?

You make it really complicated by using 3 different formulations.
You might want to work out how to mix them to get one formulation that you can use all the time.
For example, if you mix the 5 - 0 - 1 equally with the 0 - 5 - 4, you will get 2.5 - 2.5 - 2.5. (because you are diluting each one by 50%)
If you mixed them 66/33 you would get something like 3.3 - 1.7 - 2. That kind of thing....
So if you sit down with a calculator and write down all the figures and giving and taking here and there, you might just make it to something close to 1 - 0.4 - 1.5! ....OR, you might want to give one 2 times, one 1 time, and one 3 times! My head is ready to explode just thinking about it...
But then don't forget that you need to convert from the PO2O5 and the K2O) to get the % of elements the plant is actually going to see.
Can't you get a different brand?

[abhikjha]

Hahaha, as long as my plants are not complaining, I am fine with these mathematical calculations
One last question - with my NPK sorted out, what will be your recommendation for the dosage? Is 1ml of each of three (ie 3 ml) in 3 litres of water sound right to you?

[abhikjha]

Hi Mike, thanks for the response! Sorry I didn't see your message while replying to Steve with my last post. I couldn't understand the part where you said 5 0 1 mixed with 0 5 4 will become 2.5 2.5 2.5. Why this shouldn't be a simple addition and become 5 5 5? Problem is that I can get NPK in the proportion you mentioned but there won't be any micronutrients. I can't find any brand in India who sells NPK in the desired proportion with all micronutrients. However I can buy micronutrients separately. Do you think thats a better approach?

Even if I use the dilution approach for the calculation, in my view we will still get to 1:0.4:1.3 as we are talking about ratios and not the actual value of NPK constituents. In your earlier example, instead of 5 5 5, even if it becomes 2.5 2.5 2.5, ratio will still be 1:1:1.

Here is my quick excel calculation: