orchid food

[Ray]

Originally Posted by NealW

Some of the more sophisticated growers are recommending about 100-125 ppm dissolved solids in your fertilizer solution, but I don't yet have the equipment necessary to check this.

The recommendation is 100-150 ppm N, not total dissolved solids, and no equipment necessary! If you divide 10 by the %N on the fertilizer label, the result is the teaspoons per gallon for 125 ppm N. (For metricated folks, dividing 13 by the %N give ml/L for 125 ppm N.)

I cannot claim to be an expert, but my understanding is that plants can only take up nitrate and ammonium ions. Urea (CH4N2O) can form either upon decomposition.

Studies I have read claiming orchids can take up urea directly have a couple of flaws that make me wonder about their conclusions. The issues are:

1. Urea was marked with a radioactive isotope. The isotope was detected in the plant. Could not the isotope have been carried in with a decomposition product?
2. Plants fed a strictly-nitrate diet only showed nitrate ions in the "sap". Plants fed a strictly-ammonium diet only showed ammonium ions. Both nitrate and ammonium ions were found within a plant fed with urea, so the conclusion was direct uptake, apparently ignoring the fact that it can decompose into both species and then absorbed.

[NealW]

Originally Posted by Ray

The recommendation is 100-150 ppm N, not total dissolved solids

You are right, and I did mean to write nitrogen, not dissolved solids, brain freeze I guess, all too common these days. Thanks for the formula, that will definitely come in handy.

[NealW]

Originally Posted by Ray

The recommendation is 100-150 ppm N, not total dissolved solids, and no equipment necessary! If you divide 10 by the %N on the fertilizer label, the result is the teaspoons per gallon for 125 ppm N. (For metricated folks, dividing 13 by the %N give ml/L for 125 ppm N.)

Ray, if there is a urea content to the fertilizer, should we just ignore that percentage of the nitrogen content?

thanks

Neal