Grower 101: Choosing and Using Fertilizer Injectors By Lela Kelly

How to accurately select and use the right fertilizer injector for your specific needs.

Watering and fertilizing are two tasks that take the mostamount of time in your greenhouse, and fertilizing is also one of the mostimportant. You want to get the job done quickly and accurately, meaning youwant an injector that is easy to install and maintain. Maybe you want one thatis portable. Dependability and long life are key factors to the decision makingprocess. The injector should be highly accurate and perform for years to come.Spend some time asking questions up front to help you decide on the bestinjector for your situation and application. Asking other growers what they useand why they like their injectors can be a great help in your search for theright fertilizer injector. But, before you do all that, here are a few factorsto think about.

Choosing the Correct Size

Know your flow rate.One of the most important decisions you can make is to choose the right sizeinjector for your flow rate. Flow rate is measured in gallons per minute (GPM),which is the rate water flows through water lines. Flow rate can be determinedby pipe size and water pressure, which is measured in PSI (pounds of pressureper square inch). This would only help estimate the flow rate.

Many times I ask growers how they are planning to fertilizetheir plant material. Will they be using one hose at a time? Will they be usingdrip tubes, low flow pressure compensated tubes or overhead spray nozzles? Thiswill get you much closer to finding the flow rate you need.

For example, if you plan to hand water with one hose at atime, with a 5/8-inch hose and a water breaker, you could safely use a small11-GPM fertilizer injector. That injector would allow you the flexibility touse very low flow as well as up to 11 GPM.

Another example is if you have a 1-inch line feeding 100drip tubes. Each tube can put out 0.2 GPM of water. When you multiply thosenumbers, you get 20 GPM for your flow rate. The injector you choose would needto handle at least 20 GPM in flow, so the 11-GPM injector would be too small.

The setting on your fertilizer injector. Often, the question comes up about parts permillion (ppm). Fertilizer manufacturers put directions on the back of thefertilizer bags, which tell you how to make up the ppm you need for the cropyou are growing. They list different ratios, like 1:100, and give you amountsto mix with water to dissolve their fertilizer.

The ratio 1:100 means 1 gal. of concentrated fertilizer willbe automatically injected into 99 gal. of water to make up a total of 100 gal.of water and fertilizer combined. It would be the same as starting with 99 gal.of water in a tank and adding 1 gal. of concentrated fertilizer solution tomake up 100 gal. Your fertilizer injector does that automatically for you.

If you are a new grower, 1:100 is an easy place to startwhen injecting fertilizer. As you become more familiar with the ratios, you maywant to use other ratios for fertilizing.

All of these fertilizer questions can be answered free bythe fertilizer manufacturer. They have qualified professionals to help growersdecide which fertilizer to use, how often to use it and how much to use.

Choosing a Stock Tank

All fertilizer injectors draw from a concentrate tank. Thattank can be as simple as a 5-gal. bucket or garbage can. If you make up 5 gal.of concentrated fertilizer at a 1:100 ratio, you will be able to make up 500gal. of end solution.

What size tank to use depends on how much fertilizing youwant to do. It may be helpful to use an opaque tank with a lid so that you cansee the level of concentrated fertilizer every time you pass the tank. The lidis helpful in keeping debris out of the concentrate.


Filtering impurities such as sand and grit from your watersupply will not only protect your injector, it will keep all other nozzles andwatering heads free of debris.

When choosing a good filter, be sure the inside screen is adurable material, such as stainless steel. I have seen many filters in thefield that have screens with holes in them or screens that have been removed.In some cases, a disc filter may be a better choice. Also, a clean out valvecan really save time. Ask your irrigation supplier or distributor what theyrecommend.

Water Hammer

When water is moving in one direction and suddenly hits aclosed valve; that water’s energy will travel back through the water line atfour times the pressure. This surge of pressure causes water hammer. It can beextremely damaging to your fertilizer injector as well as other equipment inyour greenhouse. In order to help avoid this problem, you will need to installa check valve (one-way valve) or water hammer arrestor after your fertilizerinjector. This will prevent that surge of pressure from damaging your injector.


Most injector systems need some type of maintenance, whichallows them to run properly and accurately. Be sure to ask about what yourinjector needs to keep it running at peak performance and how often it shouldbe done.

What else can I inject with my fertilizer injector?

Most fertilizer injectors can accurately inject pesticidessuch as fungicides and insecticides. It is also a very effective way to applydisinfectants and algaecides. Be sure to check with the injector manufacturerto ensure these substances can be injected without causing harm or damage tothe unit.

Lela Kelly

Lela Kelly is vice president of Dosatron International Inc., Clearwater, Fla. She can be reached by phone at (800) 523-8499 or E-mail at [email protected]

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