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General discussion regarding the techniques and methods used to successfully grow tomato plants in containers.

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Old August 24, 2016   #1
BajaMitch
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Default What's the Deal on PPM?

Been doing some research and preparation for next year's set of container experiments focusing on fertilization variances. Ran into a problem researching the recommended PPM recipe for the macro and micro nutrients. Discovered that much information out there is inconsistent on the weight of the fert used to calculate PPM, and therefore, the recommended PPMs for the nutrients.

The most common version of PPM reflects milligrams per liter as equivalent to Parts Per Million in a solution. The problem is whether or not the PPM uses the gross weight of the fertilizer, or the compound weight or strictly the "elemental" weight of the N-P-K-Ca-Mg-S elemental nutrients.

For example, Hydor-Garden's ChemGro formulation uses the gross weight of the three fertilizers that are in their recipe for 100 gallons of solution: 1/2 lb of 4-18-38, plus 1/4 Lb of Calcium Nitrate and 1/4 Lb of Magnesium Sulfate for a total of 1 Lb. of fertilizer to make 100 gallons of solution. Their recipe says that this should be equivalent to 1200 PPM...it is, if you use the entire 1 pound as your weight for calculation of the PPM. Obviously, there are other things in the 4-18-38 fert (which come to a total gross % of 60 % (4+18+38=60). Well, what about the other 40% of that fert? Hydro-Gardens has included the weight of that 40% in calculation of the PPM = 1200.

If you use only the weight of the N-P-K-Ca-Mg-S where P= the compound P2O5 and K = the compound K2O and eliminate the 40% mentioned above, then your "compound" PPM is 533 for the Hydro-Gardens solution. If you replace the P2O5 and K2O with elemental P and elemental K, respectively, they your "elemental" PPM is 434. Big difference. Huge difference!

Deep breath. Now then, how does one know which representation of PPM is being used when you look at PPM recipes for N-P-K-Ca-Mg-S wherever you encounter it?

What my research is showing me is that the PPM recipes are all over the place. I have come across all three different PPMs and the authors never tell you which weight basis they have used in the PPM recipe. If there is enough info in the article (rarely), then I can calculate which weight basis they have used. Other than that, as far as I can tell, it's a crap shoot.

I think that most of the PPM recipes use "elemental" weight of the fertilizer, but not that sure.

If anybody has any comments on this, please post.
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Old August 24, 2016   #2
AKmark
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The good part Mitch, just follow the directions. I noticed your CaNO3 note was off though, it should be the same amount as the fert. Use the right balances that they recommend, run 1200ppm for seedlings then increase it to 1500-1700ppm when they start to bear fruit. This way you won't waste time and energy and will have super crops of tomatoes. This is what my friends and I do, it works just fine this way too. If you see a problem simply send a leaf sample to the lab, let them tell you exactly where you stand.
Haifa does list each element, but I don't bother I can just follow the directions, and a leaf sample again tells me if I am off. Produced a few tons this year again doing what I just mentioned.
Good Luck with next year.
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Old August 24, 2016   #3
Ricky Shaw
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Hydro-Gardens is using the Truncheon .70 ppm conversion, to establish a ppm TDS(total dissolved solids) from an EC (electrical conductivity) reading measured in millisiemens.

Rule of thumb for ferts (solids), 1lb in 100 gals of water will increase conductivity 1700 milliseimens (1200 ppm Truncheon)

I don't understand the weight relation to ppm, solids weigh different I'd think. So intuitively I'm thinking this is not a totally precise science, these meters. Like Mark said, I just follow directions and listen to my tomatoes. Hope that helped Mitch, about all I know.
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Old August 24, 2016   #4
Worth1
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Measuring powders by volume can be tricky to get the same amount every time.
With flour I bang the cup on the counter to pack it.
With gun powder I use a measuer and treat the measure the same every time if not you will throw off the measurements.
Like if you tap the measuer while the powder is in the measuring chamber.
Then there is the granular size to contend with.
That is about all I can help with.
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Old August 24, 2016   #5
Cole_Robbie
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I'd say to just buy a ppm meter if you want to know for sure what the ppm of your nutrient solution is. Hannah is a decent brand; Bluelab might be better. Research the care and calibration required for your meter; you'll want the calibrating solutions as well.

Also keep in mind that unless you have a reverse osmosis water filter, you're not starting with a ppm of zero. My tap water is about 250 ppm.
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Old August 24, 2016   #6
Ricky Shaw
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And if are a zero ppm, you probably need to add some hard water back in for the ferts to bond to. If not, you can get whacky meter readings. A nice source water is like 60ppm with half of that being calcium.
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Old August 24, 2016   #7
moray-eel-bite
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Ppm should be mg/kg solvent. We use a litre as a shortcut, but it's technically incorrect, as water only weighs 1 gram/ml at 4 degrees centigrade. It should always refer to the elemental makeup. Ie. 1000 ppm nacl is actually only approx. 400 ppm sodium. As sodium is approx. 40% by weight of NaCl. You can get away with calling it 1000 ppm NaCl, but if Na is all you're interested in then this isn't terribly useful.
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Old August 24, 2016   #8
Cole_Robbie
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Agreed. Cal-Mag plus Iron is a good product. Here is one brand I have used:
https://www.planetnatural.com/product/cal-mag-plus/
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Old August 25, 2016   #9
BajaMitch
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AKMark, in my post above, I used the Hydro-Gardens solution for seedlings which is 1/2 Lb + 1/4 Lb + 1/4 Lb which is 1200 PPM according to HG. The solution for 1st cluster to 4th cluster uses 1/2 Lb + 1/2 Lb + 1/4 Lb which is 1500 PPM per HG. Aside from that, I am going to use a proportioned down-size of your recipe which is 4.25 Lbs ChemGro 4-18-38, 4.25 CaNO3, 3 Lbs MgSO4, and .5 Lb KNO3 which translates to 2,876 PPM calculating PPM on the gross weight of the fertilizer recipe the same way that Hydro-Gardens derives their PPM.

One of the reasons that I posited the question on PPM calculation is because I want to inspect other PPM recipes and compare them in my process of trying to determine the best PPM recipe I can come up with. Without knowing just how they calculate PPM, it makes it pretty hard to do a comparison or even to know how to achieve they recipe using alternate ferts. My next year's experiments will include AKMarks PPM recipe, Hydro-Garden's, and various other derivations.

AKMark, got a question for you. You may never have done the calculation, but, do you have any idea as to what the average quantity of water, in gallons, used for irrigation on a per plant basis for the entire growing season? That is, how many gallons does it take to water one 5 gallon container tomato plant on the average, in your experience? For me, as far as I can calculate, one 5 Gallon tomato container and plant take about 118 gallons of water for a 5 month growing season. Any thoughts on this?
Thanks in advance, AK.

Last edited by BajaMitch; August 25, 2016 at 01:08 AM.
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Old August 25, 2016   #10
Ricky Shaw
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Again, with ppm you have to know what EC to ppm conversion the manufacturer is using. Hydro-Gardens uses .70 Truncheon and General Hydroponics uses the more popular .50 Hanna.

Mike at Hydro-Gardens uses and sells Myron meters that read .70 Truncheon. This is probably why he gets all these, "My PPM is too low." questions in the FAQ. We talked about this a couple weeks ago, he agreed and thought he'd note that going forward.

I'm sure you probably know this already Mitch, and was more for those tuning into the thread late.
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Old August 25, 2016   #11
AKmark
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Ricky, I had to set my Hanna meters at .74 to get my EC and PPM to match, interesting huh. This year I started using more MgSO4 than is recommended, I had good results too, but my length of day is almost 20 hours. This is a whole other topic though.

Mitch, I have no idea, my watering requirements are very different from Spring, to Summer, to Fall. I grew about a 1000 plants this year, 100 different varieties, in 4 different locations, everything is a little different, weather is the main factor though, and it changes daily and every year is different too. During Summer I may water 3 times per day on sunny days, once if it rains, in the fall I barely give them water once a day. It is a method that I have learned to use, I keep my cracked fruit to a minimum if I keep them evenly watered in summer, and then back off in the fall, even on BW types. I also have learned that some heirlooms do not like strong doses of fert, they bully out and fruit production is hindered.
I would not use the same MgSO4 as I use during peak season, your length of day is much different, I back off on that when my days shorten, and right now am using about 30 oz per one hundred gallons.
You can also use Flora Nova grow and about 2-3 ml per gallon of Cal-Mag for about the same results, run PPM the same, super easy. I sell that to my customers for ease of use to get wonderful results.

Last edited by AKmark; August 25, 2016 at 12:22 PM.
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Old August 25, 2016   #12
Ricky Shaw
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The Hanna's are nice that you can reset them, you steered me right. And you know what else? That little extra on MagSulfate you like, is the former recommendation, it's printed on the old sacks. Good call, I think it helped when those plants of mine came under a heavy fruit load.

.31 lbs MagSulfate vs the new at .25 lbs
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Old August 25, 2016   #13
BajaMitch
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Great, great info here. Thanks AK and Ricky.

Before you posted to this thread, Ricky, I had never heard of .70 Truncheon or .50 Hanna. All I new was that the articles that I came across used different weights to derive their PPM and made no mention as to which method they used. I had to do the three different calculations myself to determine which method the articles' authors were using and then, that way, I could do an "oranges to oranges" comparison.
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Old August 26, 2016   #14
maxjohnson
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I still have 20lbs+ of those ChemGro 4-18-38. Need to put it to good use next year.
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