DIG Add-It Fertilizer Injector For Garden Spigot, 1.5 Quart

A fertilizer injector is designed to feed fertilizer - in this case, liquid fertilizer - to your plants via your irrigation system. Add-It injectors use the specific gravity of the liquid fertilizer to ensure even distribution into your irrigation system without any pumps or moving parts. 

After filling the injector with the liquid fertilizer of your choice and turning your system on, a small amount of water is diverted from the main line into the injector body. Because the specific gravity of the fertilizer solution is higher than the water, the water floats on top of the fertilizer solution, keeping the fertilizer solution at the same strength as when you added it. The pressure differential created between the inlet and outlet of the injector draws fertilizer solution from the bottom of the injector body until all that's left is water, after which you'll need to empty the injector and add more solution if you want to keep fertilizing your plants.

Each injector model has a different "gallons to empty" spec that describes how much water the fertilizer solution is distributed amongst. The lager the body size, the more gallons it will take to empty. Remember that you won't be fertilizing your plants every time you water! Most plants only need fertilizing a few times a year. That means that even a small injector like the 1 pint model, which empties after 15 gallons, won't need to be re-filled with fertilizer every 15 gallons. You'll only need to fill it when you intend to fertilize your garden.