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 Post subject: Fertilizers?
PostPosted: Sat Apr 13, 2013 5:54 pm 
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Joined: Mon Apr 01, 2013 7:05 pm
Posts: 55
Location: Brisbane Australia
Few questions in regards to ferts, how often should i be fertilizing? What NPK ratio is desirable? I have 24/6/12 at the moment. Should the plants be sprayed or dunked?


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 Post subject: Re: Fertilizers?
PostPosted: Tue Apr 16, 2013 8:26 am 
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Joined: Fri Sep 17, 2010 7:52 am
Posts: 313
Location: Oak Island, NC
That is a far more complex question than you may realize!

I have been researching epiphyte nutrition a lot lately, and conclude that feeding very little, frequently is the best approach - I use 50 ppm N at least twice a week (divide 4 by the % N on the label - the result is teaspoons per gallon for 50 ppm N).

Orchids have adapted to capturing nutrition immediately upon exposure to it- there are sites in velamen designed specifically for that purpose. The rain cascading down through the forest canopy and down the trunks of the host trees will rarely, if ever, be more concentrated than about 15-25 ppm TDS, and most of the dissolved solids are present at the very start of the rainfall, so that adaptation make a lot of sense.

That leads me to the "spray versus dunk" question. In general, orchids are poor at foliar nutrient uptake. The plasmodesmata through which foliar uptake occurs, is closely associated with stomata on the leaves, and in orchids, 1) there are far fewer than in terrestrial plants, and 2) they tend to be concentrated on the under sides of the leaves. Add to that the waxy coatings they develop to prevent water loss, and it reduces the efficacy of foliar preceding even more. I'll also ad that the plasmodesmata preferentially admits non-polar molecules over polar ions, so while urea can be taken up through leaves (if you can apply the solutions to the right places), the nitrate and ammonium ions are very poorly absorbed. By contrast, the roots preferentially take up the ions and far less so the non polar stuff.

I'll give a couple of links to look at. The first is a general plant nutrition primer published by Bill Argo PhD in the IPA Journal a few years ago, and the second is a recent AOS article by Rick Lockwood.

http://www.firstrays.com/nutrition.htm
http://www.firstrays.com/PDF/What_Do_Orchids_Eat.pdf


Ray Barkalow
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 Post subject: Re: Fertilizers?
PostPosted: Tue Apr 16, 2013 12:07 pm 
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Joined: Sat Aug 28, 2010 3:03 pm
Posts: 7800
Location: Boston MA USA
Thanks for your reply, Ray.


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 Post subject: Re: Fertilizers?
PostPosted: Tue Apr 16, 2013 5:20 pm 
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Joined: Mon Apr 01, 2013 7:05 pm
Posts: 55
Location: Brisbane Australia
Cheers Ray, certainly a wealth of information


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 Post subject: Re: Fertilizers?
PostPosted: Wed Apr 17, 2013 6:14 am 
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Joined: Tue May 01, 2012 8:16 am
Posts: 640
Location: England in Essex.
Wow, that's certainly in depth. Thank you for the great information. I don't know how much I can, or will absorb and put into practice though.

I need better water before I worry about fertilizer or anything else :lol: . Hmmm maybe if I do loads of laundry and use only condensor water from the drier, it might be worth using a better fertilizer.


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 Post subject: Re: Fertilizers?
PostPosted: Wed Jul 03, 2013 10:42 pm 
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Joined: Wed Jul 25, 2012 8:57 am
Posts: 82
Location: Melbourne, Australia
So Ray are you suggesting we do away with the idea of 150ppm of water and stick with 50ppm instead? I've got two fertilisers to choose from:

Fertiliser A:

N: 17.7%
P: 7.9%
K: 16.0%

Fertiliser B:

N: 30
P: 4
K: 8

So based on your %/4 and assuming 1 teaspoon weighs give approximately 5grams I should be using:

Fertiliser A: 1.125g per gallon
Fertiliser B: 0.66g per gallon

and I should be using that every other watering - is that correct? I'm not very proficient in the nutrient requirements and what is best but which of the fertiliser A or B would be best? Also, you've mentioned before that you're not an advocate of modifying fertilisers during flowering cycles etc (and your logic with that arguement makes sense) so temperature would be more a driver there than nutrients in flowering of Phal species? Also, could fertiliser cause a flower spike in a P. equestris to all of a sudden start throwing out leaves at its end?


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 Post subject: Re: Fertilizers?
PostPosted: Fri Jul 19, 2013 8:46 am 
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Joined: Fri Sep 17, 2010 7:52 am
Posts: 313
Location: Oak Island, NC
Sorry for taking so long to respond!

I feed at every watering, and after learning about the concentrations in nature, decided to lower my own regimen from 100-150 ppm N down to 50. Based upon the response of my plants since doing so - more active root growth and flowering - I think I'll stick there for a while.

No need to use volumetric estimates if you have a scale, as fertilizer labels universally show weight percent nitrogen.

50 ppm = 50mg/kg, or 0.05g/kg. Your 17.7%N fertilizer is 0.177gN/g fertilizer, so you want 0.05/0.177 = 0.28g fertilizer per kilo of solution. The 30%N stuff, therefore, would require 0.05/0.3=0.167 g

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