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.

[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.

[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.

[rbarata]

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

One need to calculate based on molecular weights but will be missing the other non-quantified composts/elements and, even though, we would have to calculate the voids in between each grain of the powder...that's not something I would do, for sure.

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.

Yes, roughly the 129 ppm I've found.
I couldn't find the TDS for my tap water but I suspect it is the reason why my fertilizer solutions must be heavily shaked before use.

ES, thanks for the pointers. I also have the same idea that cooler growers need less fertilizer. Maybe that's the result of an environmental adaptation.
If I find such information condensed in one single document I will post it here.

[naoki]

Originally Posted by rbarata

One need to calculate based on molecular weights but will be missing the other non-quantified composts/elements and, even though, we would have to calculate the voids in between each grain of the powder...that's not something I would do, for sure.

No, you don't need MW to get the quantity what Ray is talking about. Teaspoon is the measure of volume, so Ray is saying that g/tsp is different for different fertilizer and different shape of measuring spoon.

To get this quantity (g/tsp), you just need a balance. You can simply measure how many milligram per given measuring spoon.

As a related note, there is a big difference in nature and under cultivation; association with mycorrhizal fungi and other endophytes. They do exist under cultivation, but it is usually at a lesser extent. Significant uptake of nutrients appears to be happening via microbes even in epiphytes (still tentative, but my friend and his team is working on it). So mineral nutrients in the stem flow may seem to low, but they may be able to get more nutrients via association.

With regard to tolerance, you should think why high TDS causes "root burn" and how nutrient uptake works. High TDS causes dehydration since water uptake is passive. Water flows toward the higher concentration region from the lower concentration region across semi-permeable membrane (cell membrane). Nutrient uptake is mostly active (even though the concentration around the root can influence the uptake rate). These two factors are conflicting, but you want to give sufficient nutrient without disturbing water uptake. After all water consumption is much higher than the consumption of mineral nutrients.

[rbarata]

No, you don't need MW to get the quantity what Ray is talking about. Teaspoon is the measure of volume, so Ray is saying that g/tsp is different for different fertilizer and different shape of measuring spoon.

To get this quantity (g/tsp), you just need a balance. You can simply measure how many milligram per given measuring spoon.

I understood what Ray explained. I was thinking about the process "from the scratch". Also forgot molecule geometry which influentiates specific weight.
The fertilizer label is not completely informative because doesn't give you the specific weight. With that info, a lot of fertilizers discussions would not exist.