A brass siphon mixer injector

Once you've decided to fertigate your garden, you should select a fertilizer injector. An injector is required to add the fertilizer to the system. Whether you have one bed or a hundred, there is a suitable model. The price of injectors ranges from a few dollars to several thousand. Fortunately, the less expensive models are compatible with most small-scale drip irrigation systems. The least expensive injector is the brass siphon mixer, which is sold under various brand names and is available at most garden centers and nurseries for around $15 to $20.

The siphon mixer is nothing more than a suction device. As water flows through the tapered orifice within the siphon mixer, the velocity rapidly increases, creating a vacuum that siphons the fertilizer concentrate from a tank or bucket into the system.

Although reasonably priced, brass siphon mixers have limitations. They are designed to be coupled with watering wands and sprinklers having flow rates of 3 gallons per minute (gpm) or higher, far in excess of many backyard drip systems' flow rates. Before purchasing a siphon mixer, determine the flow rate of your system.

Grow Pro fertilizer injector

If your drip system delivers between 1/2 and 3 gpm, consider using a Grow Pro brand injector which costs around $30. Unlike the siphon mixer, the Grow Pro has a built-in 12-ounce reservoir that you fill with a concentrated fertilizer solution before use. The existing water pressure forces the concentrate into the system and exhausts it in 50 gallons of flow. Models capable of handling higher flow rates are also available. (See the appendix for a listing of companies carrying Grow Pro and Add-It injectors.)

An EZ FLO injector equipped with a faucet switching kit

The EZ FLO injector operates on a similar principle as the Grow Pro injector. A small amount of irrigation water is diverted through the fertilizer tank where it mixes with soluble fertilizer before being injected into the irrigation system. The EZ FLO is an upgrade over the Grow Pro as it is equipped with an adjustable injection rate control. EZ FLO injectors are available in 3/4-, 1 1/3- and 3-gallon models. The 3/4-gal model is priced around $70 which includes a faucet switching kit. The switching kit is recommended for folks who need a quick way of switching out the injector from one drip system to another. (See the appendix for a listing of companies carrying EZ FLO injectors.)

A fourth type of injector compatible with both small and large drip systems can be assembled from a new or used pump-up hand sprayer and a few pipe fittings for under $50. This contraption, affectionately referred to as the "pump-it" injector, relies on air pressure generated by the hand-operated pump to force fertilizer concentrate into the system.