Automatic fertilizer injectors are the popular gimmick of the moment.  I really don’t find them all that convenient, it seems just as easy to spray fertilizer with a sprayer and be able to put it where I want it as it is to calibrate the fertilizer injector.  With that said, it seems everyone wants a fertilizer injector lately for some reason.

I’m not a huge fan of fertilizer injectors, especially for sprinkler systems.  For drip systems it makes more sense, as the fertilizer water is not sprayed into the air.  I think fertilizer injectors are excellent for agricultural crops, but not nearly as well suited for home landscapes.  A few of the issues:
1. First is control, the fertilizer gets applied at the same rate to everything.  Different plants need different amounts of fertilizer.
2. Second is uniformity, if the fertilizer isn’t evenly mixed into the water you can get burning of foliage.  The maker of the fertilizer injector will have recommendations for addressing this issue.  Generally it just means you need to have several feet of pipe between the injector and the first sprinkler head or drip emitter.
3. Third is health, most sprinklers produce mist which drifts easily to adjacent property.  Without care it can contaminate or cause sickness.  The EPA has strict rules regulating maximum wind speed that can occur during chemical applications using aerial spray nozzles.  Generally what this boils down to is that the fertilizer injection should be manually controlled and only used when someone is supervising the system.
4. Backflow prevention- because the fertilizers are chemical injection (high hazard) a reduced pressure backflow preventer is technically the only type of backflow preventer that is satisfactory.  They are very expensive and few homeowners have them.  Talk to your water provider about the specific requirements for your area.
5. Runoff- most residential sprinkler systems have substantial runoff.  With fertilizer in the water this can cause environmental problems with storm-water drainage disposal.  This high nutrient content runoff water causes algae blooms in lakes and estuaries, and also encourages growth of non-native weed species along streams and rivers.
6. If the fertilizer sprays onto a car it must be washed off immediately.  If it drifts onto your neighbors car and sits all night the fertilizer can damage the paint.
7. Nitrogen, the primary nutrient you will be applying,  is easily volatilized (evaporated) into the air.  This means that when you spray fertilizer as a liquid into the air you loose some of the nitrogen.  Two factors heavily influence this.  Volatilization is a much greater problem with warmer temperatures and it also increases if the water droplets are smaller.

If you can address all the above issues, then it is a great thing.  In agricultural situations with a single crop and strict supervision this is efficient and easy.  Homeowners tend to be looking at fertilizer injectors as a “set it and forget it” solution.  It is not.  It requires much more work than either broadcast or hand applied foliar fertilization methods.  Very few commercial landscapers use injectors, high costs and labor requirements for supervision, combined with liability exposure for poisoning pets and people are the reason.

I prefer hand applied foliar treatments where the level of control is much higher.  Only the plants that need more fertilizer get it.  I am a big fan of foliar applied fertilizer using a sprayer.  It is much more efficient than broadcast fertilizer, works faster, and typically results in less environmental pollution.