Calculating Fertilizer JXxnounts i n Greeulk.louses

Dustin Blake!

This handout n i l l shon you lion to calculate an amount of d n fertilizer to add to water to make a g iwn concentration of fertilizer solution

Recommendations of diluted fertilizer solutions used on plants are given in parts per million (ppm). There are 10,000 ppm in a 1% solution, The N-P-K numbers on :I fertilizer bag are percentage anal!.sis of the d T niix. Most fertilizer recommendations are made for balanced fertilizer formulations and are quoted in terms of the ainount of Nitrogen to add. Use the N-value on the bag and everything else (P,K. micros. etc.) will be taken care of for you.

The fonnulas below will show you how to mix these so that a final concentration may be obtained, The first formula can be used to find the concentration of a solution that will be directly applied to the plants from a watering can, for instance. The second formula will allow you to find how much concentrate of fertilizer solution to make. This will be used as the source for your injector. The concentration that tvill come out of the hose will be the final dilution that you desire.

A nile of thumb I h e I S to use 125 ppin constant feed on plants that spend part of their gro\\ing c!cle 111 cool weather and to use 250 ppin for plants that thri\c 111 heat Altern,ite 125 ppin and clear nater for impatiens. tropical houseplants, and vegetable transplants Don’t feed seeds until the first tnie leaves are open. and then feed sparinglj until roots reach tlie side of the container

Formula 1: No Injector

desired pprn / 75 ...................... = S oz fertilizer / gallon solution YO nutrient analysis

Example: To make a 200 ppin concentration of Nitrogcii of a 20-10-20 fertilizer:

200 1 7 5 / 20 = 0.13 oz 20-10-20 I gallon

Formula 2: With an Injector

Result of formula 1 x ratio of water to conc. solution corning out of hose = .Y oz fertilizer per gallon of concentrated solution going into injector.

Example Using a SiphoneuT%f injector (15 1). !ou nant to make a concentrate solution of 15-5-15 that will have 250 ppin coining out of the hose You nil1 fill a 5 gAloii bucket nit11 this solution

Use formula 1: 250 / 75 / 15 = 0.22 oz / gallon Now use formula 2 : 0.22 * I 5 = 3.3 oz / gallon of concentratc. Finally, fill the bucket: 3.3 oz / gallon * 5 gallons = 16.7 O L in 5 gallons of nater.

So add 1 pound of the fertilizer into 5 gallons ivnriii water. SLir. Insert feed line from injector into the tank

Note: precision is not really that important. Rounding off is OK.