Fertilizer Injectors

These devices let you fertilize plants while you drip-irrigate them How do you fertilize plants watered by drip irrigation? You can't spread granular fertilizer because it would reach roots only where emitters wash it into the soil. And controlled-release fertilizers worked into the ground at planting time only last so long. You could walk from plant to plant, giving each a dose of diluted liquid fertilizer, but that would defeat the labor-saving benefits of a drip system. The easiest way to feed plants on drip is to slowly introduce nutrients directly into the water line. Two devices let you do just that; either can be hooked into a new or existing drip system.

Dissolvers use fertilizer tablets You can get nutrients to your plants using fertilizer tablets. They are loaded into a simple dissolver attached to your water source, as shown above, or attached just before your filter. Water flows through the unit and slowly dissolves the tablets, releasing nutrients into the drip system. The number of tablets you insert depends on the system; follow the manufacturer's guidelines that come with the unit. If tablets fit, they can be inserted into the Y-type filter, creating a simple dissolver. But never do this with liquid or water-soluble dry fertilizers; they may severely burn your plants. Most dissolvers cost less than $10 and hook up in minutes. Some units have a built-in backflow device to keep fertilizer from siphoning back into your household water supply. If not, you'll have to position a backflow device (check local plumbing codes for requirements) between the water source and the dissolver. The drawback with dissolvers is that you must use the manufacturer's tablets, which are expensive for the amount of nutrients in them (about $3.50 for 10 tablets). Also, you can't increase fertilizer concentration to accommodate more emitters; all you can do is fertilize oftener.

Injectors pump in liquid fertilizer These units slowly add liquid or water-soluble dry nutrients to your drip system. The injector fits into your water line after a backflow device and before a filter and regulator. In areas with water pressure over 80 psi, place the regulator before the injector and filter. Your water department can provide information on water pressure. To fill the injector, you pour liquid fertilizer (not fish emulsion--it can clog emitters) or dissolved dry nutrients into the plastic reservoir. Pressure differences within the injector cause the fertilizer to be sucked into the water line, then distributed to your plants. Three factors determine how much fertilizer you need: the number of emitters in your drip system (more emitters, more fertilizer), manufacturer's specifications, and the fertilizer's dilution rate. Injector directions should tell you how much fertilizer to use. Using liquid fertilizers limits the amount of nutrients you can inject into a system at a given time. For example, you can add only 1 pint of fertilizer to a 1-pint reservoir, and you can't increase the concentration. However, you can simply fertilize more often to get the amount of nutrients you need for the number of emitters in your system. With water-soluble dry fertilizer, you can mix a more concentrated solution. Just add dry fertilizer to water until you get the concentration you need. Injectors range from $15 to $60 (most are about $35), not including filter and pressure regulator.