How to Calculate Fertilizer Amount

[Corbin]

I have been doing some research and found the following formula for calculating the amount of fertilizer to add to reach a desired ppm of nitrogen. The formula is from David Mellard's article in the August 04 issue of the Atlanta Orchid Society's newsletter. See also Part 5 of Bill Argo's article in the Sept. AtOS newsletter.

step 1) Multiply the desired nitrogen concentration by the gallons of fertilizer you want.
step 2) Multiply the percent nitrogen in the formula by 75
step 3) Divide the value from Step 1 by the value from Step 2

Amount of fert. to add = (desired nitrogen concentration) X (# gallons of water) / (% nitrogen in the fertilizer) X (75)

Example: If you want 125 ppm nitrogen in one gallon of water and the fertilizer is 20-10-10

(125) X (1) / (20) X (75) = 0.083 ounces

Since 1 tsp holds about 0.2 ounces then 0.083 ounces divided by 0.2 ounces per tsp = 0.4 tsp

 

[Ernie]

If I remember right, there is a really nifty calculator for this on First Rays site???

-Ernie

 

[neo-guy]

Thanks for the tip. I suggest your formula is more accurate written this way:

(125 X 1) / (20 X 75) = 0.083 ounces

Is 125ppm of nitrogen the recommended amount for Orchids?

Peter

 

[Corbin]

125 ppm is just an example though that seems to be the recommended ppm for MSU fert. However if when using MSU you want 125 ppm nitrogen would that not be the desired concentration with any fert?

 

[Jim Toomey]

125 PPN nitrogen is a great place to start.
It is a great overall amount for a wide variety of orchids. This is useful if you have a wide varity of orchids and do not want to have a bunch of different solutions around and keep track of.