A Fertilizer Discussion Reprise

[Shadeflower]

Found a great video on the subject.

Another self watering grower, so there's quite a few I've found on youtube by now!

The reason I link this specific video is because it answers so many questions I've had about fertilizing and she has confirmed that 100-300ppm is the right level and explains in the best detail when to feed what. (species vs hybrids, root thickness, size of plant, growing season etc)

It's briliant, it's exactly the video I was hoping to find so here it is people:

Fertilizing #Oncidiums the EASY way | Avoid mineral deposits | Inorganic Organic Media #MarijaZuro - YouTube

[Ray]

Originally Posted by Shadeflower

The reason I link this specific video is because it answers so many questions I've had about fertilizing and she has confirmed that 100-300ppm is the right level and explains in the best detail when to feed what.

Is that ppm N or ppm TDS?

I suspect the latter, but that still isn't all that specific due to fertilizer formula variations.

For example, the MSU WW formula @ 100 and 300 ppm TDS, respectively, will contain 19 & 57 ppm N. MSU RO at those same TDS levels will contain 16 and 41 ppm N, and K-Lite will have 13 and 39 ppm N.

All that variation from three formulas that are all made by the same company using the same ingredients, so Imagine what it could happen if you use different manufacturers' formulas.

[Shadeflower]

Ray those numbers are all too similar to make any meaningful difference though

She is talking about Total dissolved solids (TDS)

So to illustrate, I will detail my new feeding regime with Rainmix,Kelpmax and magnesium:

low dose (0.5g per gallon Rainmix + 0.5g epsom salt per gallon + 0.2ml Kelpmax per gallon): ~160ppm TDS
High dose (1g per gallon Rainmix + 0.5g epsom salt per gallon + 0.2ml kelpmax per gallon) : ~240ppm TDS

Ok so what does that mean? Lets break it down.

The formula for Rainmix is 11,8%N + 2,7%P2O5 + 13,7%K2O + 11,8%CAO + 3,5%MGO + 4,8%SO3

So for my low rate this will work out as roughly:
30 ppm N
8 ppm P
32 ppm K
30 ppm Ca
8+12 = 20 ppm magnesium
15+17 = 32 ppm Sulphur

Total: 152 ppm TDS

For my summer rate this will work out as roughly:
50 ppm N
12 ppm P
55ppm K
50 ppm Ca
16+12 = 28 ppm Mg
25+17 = 42 ppm Su

Total: 237 ppm TDS

I used the ratio of nutrients to work out how much of each macro nutrient would be present in a 160ppm and 240ppm solution respectively. The micro nutrients will not affect the TDS significantly.

I will be adding epsom salt at half a gram per gallon of water for my added magnesium content and it was hard to find accurate information on magnesium but I think that amount adds 12ppm Mg and 17ppm Sulphur so those numbers have been added. It registers as a 40ppm increase to TDS so it might be slightly more or there are other elements in Epsom Salt but these are just rough numbers anyway.

They should be roughly right but there can be a bit of variance as long as one does not go above 500 ppm TDS which I know people do do but I don't think one should ever go above 500.

My numbers are still on the conservative side and the bigger the orchid and the warmer your climate you might need a bit more.

Up till now throughout this year I have been using my new low rate but I have decided to increase to my new high rate for my bigger orchids throughout summer next year. At ~120 ppm (without magnesium) which is as low as I was feeding at times I feel like some of my bigger orchids are telling me they want more.
That is debatable but I think so.

Anyway if it helps anyone, the breakdown is a bit meaningless unless you are a scientist really but it did help me decide I was a bit low on magnesium which I have upped now.

I think my numbers are correct but like said it can be hard to get the exact dose that epsom salt will add.

[Ray]

Originally Posted by Shadeflower

So to illustrate, I will detail my new feeding regime with Rainmix,Kelpmax and magnesium:

low dose (0.5g per gallon Rainmix + 0.5g epsom salt per gallon + 0.2ml Kelpmax per gallon): ~160ppm TDS
High dose (1g per gallon Rainmix + 0.5g epsom salt per gallon + 0.2ml kelpmax per gallon) : ~240ppm TDS = 20 ppm magnesium
15+17 = 32 ppm Sulphur

Total: 152 ppm TDS

For my summer rate this will work out as roughly:
50 ppm N
12 ppm P
55ppm K
50 ppm Ca
16+12 = 28 ppm Mg
25+17 = 42 ppm Su

Total: 237 ppm TDS

Sorry, but I have to question the accuracy of those numbers. Rain Mix and MSU RO have very similar formulas, and the MSU RO formula mixed at 1g/gal has a true TDS of 264 ppm, all by itself. Once you add Epsom Salts and KelpMax, it’ll be even higher.

If you’re reading that with a TDS meter, the error is to be expected, as they are highly inaccurate.

As far as your calculated summer rate is concerned, you seem to have disregarded that everything in the fertilizer contributes to the dissolved solids level, or just selected cations.

I’m not trying to shoot holes in your growing regimen, but am trying to point out that managing any feeding regimen via TDS - unless of course your meter has been calibrated using your specific irrigation blend - can be deceiving, and makes it difficult to compare with others’.

[Shadeflower]

thx Ray,
I already said that my numbers are rough numbers and that adding the Epsom salt increases the ppm by 40ppm.

Granted my ppm meter is just a £6 meter but it registers the changes as I make them which is good enough for me.

You are saying the MSU at 1g/ gallon works out at 264 ppm.

I have said that 1g/gallon of Rainmix (which is a different mix of nutrients entirely) comes to roughly 200ppm(60ppm rainwater+ 140ppm fertilizer) on my cheap ppm meter.
Then adding the Epsom salt adds roughly 40 ppm to give a total of 240ppm.

This is quite a bit lower than the equivalent of the MSU formula. I haven't got any MSU to compare to my Rainmix. One explanation is that Rainmix is weaker, using 12% N whereas I think the MSU might be 18% N so using the same amount will add 50%-100% more to the overall ppm.

But that doesn't make my numbers any less accurate, that just means one has to work out how much MSU to use which I have done for my Rainmix to come to those numbers.
Without a ppm meter that would be hard as like you say 1g of Rainmix comes out at roughly 140ppm and 1g of MSU comes out at 264. But if I wanted to make a 264 ppm solution I would just add 50%-100% more Rainmix and the values would be the same again.


Based on the formula one can work out roughly how much of each Nutrient makes up that number.

Bear in mind I did not even take into account the initial ~60 ppm that my rain water has which I have no clue of what nutrients that is made up of.

So it is all rather hypothetical. We don't even know for sure what the right ratio is.

Is K-lite the right ratio, the other MSU formula's, Rainmix, or something completely different?

You will notice all I have tried to work out is the minimum that orchids need (roughly 25ppm N and similar numbers for the other macro nutrients I have listed) .

Then like mentioned I feel this is the minimum amount though and my new higher rate is 50ppm N with K and Ca being in the same ratio.

To me it sounds like 1g/gallon of Rainmix is the equivalent of using 0.5g/gallon of MSU.

I have not worked out the numbers now but based on 1g/gallon being 264ppm I am guessing half the amount is the same as the Rainmix (if the ratio of nutrients are the same which I think they roughly are)

This is to be expected if you compare a 20-20-20 to a 10-10-10 nutrient for example.

Tbh my calculation were just to illustrate for any concentration that a ppm meter shows one can with the formula of the fertilizer work out the breakdown of those nutrients. Whether they are exactly correct is to me irrelevant as we don't even know what the exact numbers should be.

Already just looking at the bottle of the Rainmix we can see that N is 12%, Ca is 12%, so that's fine but Mg is only 3% which is a bit low!

Hence my trial of Epsom salts from now on. It's really not as difficult as it seems. Whether adding epsom salt will make any difference that is to be seen now.

so edit: MSU Fertilizer is - 19-4-23 - Well Water Blend which a expected will be more concentrated than the Rain mix. which is 12-3-14

So without a ppm meter, one is just guessing anyway whether the ppm is calibrated 100% or 99% accurately is not important.

The first thing one needs is a ppm meter

Then the only reason I have made the breakdown to see what that ppm number my meter is reading works out to be is to see how much epsom salt to add!

You will notice I worked out I need to add the same amount for my low rate and my high rate.

Without the breakdown I would have assumed I should add twice the magnesium for my high rate which I don't believe is needed, I also would not have known how much to add.

I think I have made this far more complicated than it needed to be.

I just wanted to know ok based on the fact my Rainmix has 3% Mg and should have 6% Mg, how many grams of epsom salt do I need to add?

That is what this has all been about and like mentioned I have worked out this should be a half a gram per gallon which adds 12 ppm of Epsom salt

The Kelpmax, you are correct I did completely ignore throughout my calculations but that is because in the quantities I use I believe it adds 3ppm overall to the total TDS.

Edit 2: Notice I use 0.2ml per gallon. That works out as 0.05ml per liter. Not 0.5 but 0.05ml.
Like said I think it adds 3 ppm so I disregarded that throughout my calculation.

[WaterWitchin]

All I can say is these calculations make my head hurt and my eyes glaze over. Please don’t let my orchids know this.

[Shadeflower]

I feel you WW, which is why I rely on my ppm meter.

The ppm meter is invaluable to get a rough idea.

I mean take the MSU at 19-4-23 at 1 gram per gallon that works out as 264ppm

1 gram per gallon of 12-3-14 Rainmix works out as 140ppm

So like mentioned with a ppm meter we can easily see to have the same mix we need to use half the amount of MSU as Rainmix

Both will give roughly 50ppm N like this but without a ppm meter we would have no clue.

The labels on the fertilize bottles are notoriously all over the place, my bottle tells me to feed 4 times stronger than I do.

Hence why you need a ppm meter.

Why do we know that the msu has a ppm of 264?

Yep because someone decided to stick a ppm meter in the bucket and check... That's all it is.

[estación seca]

There is no such thing as a PPM meter and there is no such thing as a TDS meter. It's physically impossible to make something like that for mixed chemicals dissolved in water. Have you ever taken a chemistry class?

[Shadeflower]

ES that is your belief, if you type it in to Amazon they do sell them.

Whether you want to believe they exist or work is entirely up to you.

Jjust like I could argue clocks don't work. Thermometers don't work, ie they are inaccurate.

So throw all thermometers in the bin, never rely on the clocks, they are always seconds off. Thermometers are not needed, just stick out a wet finger to measure and I dunno taste the fertilzer water I suppose but to me relying on technology helps me.

I know my thermometer can be as much as 1 degree off but I still use them and that is good enough for me. Atleast I know roughly what I am measuring.

It's the same with a ppm meter. They might be an innaccurate EC meter but so is a thermometer. You can either chose to use one or not.

Fine by me either way but I love my ppm meter and I would be lost without my thermometers.

[wisdomseeker]

Originally Posted by estación seca

There is no such thing as a PPM meter and there is no such thing as a TDS meter.

I'm confused about this, and don't fully understand.

There are several quality TDS bench meters (various brands) that are frequently used in the water/wastewater field that are fairly accurate with their test results.

Relationship Between TS, TSS and TDS

Solids, Total and Dissolved (TSS and TDS) - Water Quality Parameters | Hach