Grower 101: Choosing and Using Fertilizer Injectors

October 3, 2003 - 06:31

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

Watering and fertilizing are two tasks that take the most
amount of time in your greenhouse, and fertilizing is also one of the most
important. You want to get the job done quickly and accurately, meaning you
want an injector that is easy to install and maintain. Maybe you want one that
is portable. Dependability and long life are key factors to the decision making
process. 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 best
injector for your situation and application. Asking other growers what they use
and why they like their injectors can be a great help in your search for the
right fertilizer injector. But, before you do all that, here are a few factors
to think about.

Choosing the Correct Size

Know your flow rate.
One of the most important decisions you can make is to choose the right size
injector 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 determined
by pipe size and water pressure, which is measured in PSI (pounds of pressure
per square inch). This would only help estimate the flow rate.

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

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

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

The setting on your fertilizer injector style='font-weight:normal'>. Often, the question comes up about parts per
million (ppm). Fertilizer manufacturers put directions on the back of the
fertilizer bags, which tell you how to make up the ppm you need for the crop
you are growing. They list different ratios, like 1:100, and give you amounts
to mix with water to dissolve their fertilizer.

The ratio 1:100 means 1 gal. of concentrated fertilizer will
be 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 to
make up 100 gal. Your fertilizer injector does that automatically for you.

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

All of these fertilizer questions can be answered free by
the fertilizer manufacturer. They have qualified professionals to help growers
decide 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. That
tank 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 500
gal. of end solution.

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


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

When choosing a good filter, be sure the inside screen is a
durable material, such as stainless steel. I have seen many filters in the
field 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 valve
can really save time. Ask your irrigation supplier or distributor what they

Water Hammer

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


Most injector systems need some type of maintenance, which
allows them to run properly and accurately. Be sure to ask about what your
injector needs to keep it running at peak performance and how often it should
be done.

What else can I inject with my fertilizer injector?

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

About The Author

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 lela.kelly@

Leave A Comment

  • Web page addresses and e-mail addresses turn into links automatically.
  • Allowed HTML tags: <a> <em> <strong> <cite> <code> <ul> <ol> <li> <dl> <dt> <dd>
  • Lines and paragraphs break automatically.

More information about formatting options

By submitting this form, you accept the Mollom privacy policy.