First Post... and Orchidgain dilution rates?

[CMroz]

Thanks again to everyone for their input. Because I'm a bit of a nerd I decided to convert Ray's post into an interactive spreadsheet. It will save me some work in the future if my fertilizer or concentrations change.

I thought I would share it here in case anyone else finds it useful:

Fertilizer Calculator

If you notice that I botched something in the formulas please let me know and I'll fix it.

[Ray]

Originally Posted by CMroz

<edited by Ray>I'll admit I still don't know the exact conversion factor/formula used to derive the "2.9g/gal" requirement - but I have no problem taking your word for it and mixing up a concentrated batch!

It's actually some simple math:

• Nitrogen content on fertilizer labels is weight percent.
• Nitrogen ppm is weight per million.

Take those and the percentage of the fertilizer weight that's N, and you can calculate the amount of fertilizer needed to provide the final, desired ppm.

HOWEVER, based upon your comment, I just built a Fertilizer Mixing Calculator Using Nitrogen Concentration that will do it for you.

[marcmaubert]

I'm confused about the 25-50 ppm at every watering. I thought I read "125 ppm every week". How many times per week should I water? I converted my orchids to S/H this year so I could be a little bit more "lazy" about watering all of them, so I do it only once a week (only my NOID Oncidium seems to gulp down all of the water in the reservoir in a matter of days). Is that wrong?

[estación seca]

marcmaubtert, Welcome to the Orchid Board!

If the solution is 25-50 ppm in the reservoir, the roots are receiving that all the time. You can think of it as watering every day at 25-50 ppm. 6 x 25 = 125. Watering once a week with 125 ppm makes available to the roots the same amount of fertilizer as watering 6 times a week with 25 ppm.

[marcmaubert]

Oh, that makes sense. Thank you so much! Seems like I've been overfertilizing for months and haven't noticed any leaf tip or root tip burn. Is it because the new roots haven't reached the reservoir?

[Ray]

Assuming you water correctly (flooding the pot, letting it fill to the top, then drain), then your plants are getting whatever you're applying.

When the MSU RO formula was first out, I followed their recommendations about using 125 ppm N, and did so at every watering. The plants grew fine, and there was no evidence of any "burning", but after a year or two, blooming was almost nonexistent.

When I changed to 25 ppm N, they rebounded wonderfully after a few months.

[estación seca]

So long as there is liquid in the reservoir, the roots don't need to be in the reservoir; they get the liquid wicking up the medium. 125 ppm is not that much for many orchids if you're using pure water. It just isn't necessary to use so much fertilizer.

[marcmaubert]

Great, I don't want to waste money on more fertilizer if it's not going to benefit my orchids. Thanks for all the help!

[estación seca]

We would love to see your collection and learn more about growing in México.

[CMroz]

Thanks for adding that handy calculator to your site Ray! I know it' probably a straightforward formula for most people who think about ppm regularly, but I hadn't ever needed to calculate it before. The one number that actually tripped me up the first time around was the 3785.41 conversion factor - once I understood that the rest was pretty clear!