Fertilizer ppm question

[rbarata]

When someone advise to water with a fert concentration of 150ppm is it N ppm or NPK ppm?

[Ray]

Could be either.

I used 25 ppm N, and my TDS was about 150 ppm.

150 ppm N is acceptable for infrequent feeding, but the TDS will be about 900 ppm, with most fertilizers.

[rbarata]

I got some advise from fellow board members to water with a 150 ppm solution.

My NPK is 13-3-15 and the recommend concentration is 1/2 gr per 5 liters (1 teaspoon/0,75 gallon).

Result:
ppm TDS (N+P+K only)=265
ppm N=129

So I assume these recommendations are referenced to N only.

[Shadeflower]

Originally Posted by rbarata

I got some advise from fellow board members to water with a 150 ppm solution.

My NPK is 13-3-15 and the recommend concentration is 1/2 gr per 5 liters (1 teaspoon/0,75 gallon).

Result:
ppm TDS (N+P+K only)=265
ppm N=129

So I assume these recommendations are referenced to N only.

Sorry for dragging up a 4 year old post. I have just done the calculations for my own fertilizer as I detailed in a different thread and came across this one to compare my numbers.

So it seems my math is all correct. This can be verified via Ray's ppm calculator:

Fertilizer PPM Calculator › First Rays LLC

So everything posted in this thread matches my numbers so far except this statement ^^

At 265ppm TDS there is no way that the N content (being 13%) will come out at 129 ppm N...

I don't even know what values to add into the calculator.

Rbarata, I know you still frequent this site and I know this was a long time ago in which time you will have a better understanding so maybe we can rectify these wrong numbers.

you say you added 0.5grams per 5 liters but then also say this works out as 4.2grams(1 teaspoon) per 0.75 gallons.
If I convert that it works out as 4.2grams per 2.85 liters or 1.5 grams per liter.

so which number do I put into Ray's calculator?
0.1 grams per liter or 1.5 grams per liter?

The one gives an N value of 16 ppm
The other gives a value of 234 ppm N

Quite a bit of discrepancy from the 129 ppm N which like said was impossible also as 13% of 265 ppm should be much lower, I'd estimate 30-50 ppm N (according to the calcuator at 1g/gallon it would be 33 ppm N)

Not surprised people get confused by these calculations

Anyway, I know this is 4 years old so old news but new members like to know how much to feed.

I think the feeding chart by ES is pretty good apart from the Vanda feeding rates (based on me having caused root burn using over 500ppm but that is a matter of opinion)

[estación seca]

I think most orchidists refer only to N when talking about PPM for fertilizer. The assumption is fairly pure water will be used, like rain or reverse osmosis, which means the TDS with fertilizer won't usually be a problem for most plants.

Fred Clarke at SVO told me 1/8 tsp / 0.625ml of powdered MSU formula for pure water, per gallon / 3.78 liters, of rain or reverse osmosis water, is close to the maximum TDS for growing Paphiopedilums. Most other non-miniature orchids have higher, to much higher, tolerances for TDS.

Depending on how often you can water and prepare fertilizer solution, it is safer to use a lower concentration more often than a higher concentration all the time - except with those few orchids that like higher concentrations all the time while in growth.

If you haven't read all of Ray's information on fertilizer on his Web site, I strongly recommend it. He has a calculator for ppm N based on amount of powder used.

[rbarata]

I know Ray's information and calculator also.
About fert concentrations I know where I stand but I really don't know much about max TDS for each genera.
I wonder if there's any site where to find it all together like a table, for ex.).

[estación seca]

What little I know about maximum TDS tolerance has been from my reading here and there. What follows is from my impressions and memory only; I cannot give references.

My impression is cooler growing plants are more likely to be intolerant of higher TDS in water. Plants from the beach tolerate a lot more (accustomed to, but not requiring, salt spray.) Some are just surprises.

I think all epiphytic orchids can be grown well with rain or reverse osmosis water. If either be readily available and not too expensive I would use only those - and I do. I use my tap water for non-fertilizer watering of my Vandas (see below.)

Some people have tap or well water with low TDS. This is great for orchids. New York City is an example. A friend in the extreme east of metro Phoenix has well water great for most orchids, under 100 ppm TDS. I have tap water with 600-1200 ppm TDS depending on time of year. A gardening friend four blocks from my house actually measured his at 900 ppm on several occasions.

Some guesses at routine TDS acceptable for orchids. This is for regular watering, not fertilizing.

I have been told 1/8 tsp / 0.625ml, of MSU for pure water dry fertilizer powder, per gallon / 3.78 liter pure water, yields around 50 ppm TDS. I have neither measured nor calculated this number. If somebody demonstrates otherwise I will come back and change this message.

Paphiopedilum 50 ppm and under preferred. (Advice from Fred Clarke at SVO.)
Phragmipedium even less.
Cloud forest plants 50 ppm or less.
Cattleya, Miltoniopsis, Oncidium, Phalaenopsis 200-600+ ppm max but lower always better.
Former Odontoglossum (and hybrids?) need well below other Oncidium.
Tolumnia seem to do fine with Phoenix tap water 600-1200 ppm TDS (I use rain when I fertilize.)
Vanda are grown commercially with Florida well water, among the highest PPM water in the US. They do fine here with Phoenix tap water 600-1200 ppm TDS (I use rain when I fertilize.)

Paphs with Phoenix tap water brown from the tips and die over 3-6 months. Catts and Phals live for years with Phoenix tap water but often have brown tips; they don't thrive.

[D_novice]

Originally Posted by estación seca

Paphiopedilum 50 ppm and under preferred. (Advice from Fred Clarke at SVO.)

While I'm not going to question Fred Clarke's Paph acumen, the Huntington Museum has one of the world's greatest Paph collections, and their water is 200-800 PPM, per an article in one of the journals (maybe the CSA).

I ask for lots of opinions in order to learn as much as possible - including on this forum - but as in life, I've noticed that basically no one knows anything for sure.

[Ray]

Per the manufacturer, 1.45g/gal will yield a 50 ppm N solution.

Translating mass to powder volume (especially heterogeneous ones like the Greencare MSU formulas) is damned difficult and inaccurate.

That said, dividing 4 by the %N on the label is a way to estimate the teaspoons/gal for 50 ppm N, so 1/8 tsp/gal of a 13%N formula is more like 15 ppm N.

Personally, I think the discussion of what TDS a plant can tolerate is of no value. These guys have evolved to expect very little food, provided in many, small doses, so it makes sense that mimicking that is the better approach.

Humans can "tolerate" a booze binge, but doing that periodically will be ultimately harmful, while a small amount, consumed regularly, has been shown to have health benefits.

[estación seca]

Originally Posted by Ray

Per the manufacturer, 1.45g/gal will yield a 50 ppm N solution.

Translating mass to powder volume (especially heterogeneous ones like the Greencare MSU formulas) is damned difficult and inaccurate.

That said, dividing 4 by the %N on the label is a way to estimate the teaspoons/gal for 50 ppm N, so 1/8 tsp/gal of a 13%N formula is more like 15 ppm N.

Personally, I think the discussion of what TDS a plant can tolerate is of no value. These guys have evolved to expect very little food, provided in many, small doses, so it makes sense that mimicking that is the better approach.

Humans can "tolerate" a booze binge, but doing that periodically will be ultimately harmful, while a small amount, consumed regularly, has been shown to have health benefits.

Fred meant 50 ppm total dissolved solids, not just N. He made this clear in the discussion.

I reported elsewhere here on Orchid Board Brandon Tam's lecture to our orchid society about how the Huntington grows Paphs.

---------- Post added at 09:13 PM ---------- Previous post was at 08:57 PM ----------

As Naoki pointed out, some nutrients are actively taken up by roots. That means the plant expends energy absorbing these nutrients. Water tends to flow passively, replacing that transpired when stomata are open.

Some nutrients - calcium is an example - are excluded from most plant roots, except at the narrow collar near the root tip. I don't know whether this calcium exclusion is found in orchid roots. Without this plants would be flooded with calcium, a common mineral in most ground water. This mineral plays a part in regulating enzymatic activity inside plants, just as in animals, so too much calcium would be fatal.

Root "burn" is often an osmotic issue. In other words, it is mainly related to the number of dissolved osmotically active particles in the solution - if the external water solution has a higher particle concentration than the plant, water flows out of the plant through the roots, or the plant is unable to take up water. This leads to root death.

Nutrition is different from water balance. What growers are interested in is providing sufficient nutrients to plants without causing an osmotic problem at the roots, or preventing adequate water uptake. Orchids don't need much nutrition, but they do need a lot of water.

Electrical conductivity measures the number of particles carrying an electrical charge in the solution. It can't be translated to TDS without knowing exactly what chemical species are in the solution, and in what amounts.

EC can be used to compare relative proportions of the exact same mineral mixture added to water, so it can be used to measure fractions or multiples of a known constant concentration of a particular fertilizer product of unvarying composition, when mixed in different volumes of water. EC can't provide much useful information for a solution of unknown composition.

It is possible to have a solution with very low EC that has so many osmotically active particles roots would be killed - an example would be a concentrated solution of table sugar.

During periods of high humidity, most fertilizer powders absorb water from the atmosphere, without much changing the volume in the container. That quarter-teaspoon will weigh more during humid times than in arid times.

Fortunately for us orchids don't need much fertilizer.