SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

Strictly for the money, you probably don't get one of these. If you inject fertilizer into a sprinkler system, you will end up needing an RPZ backflow preventor, because you are injecting a foreign substance into the water under pressure, and nothing less than an RPZ is rated for toxic backpressure. A tablet-type fertilizer (think of swimming pool chlorine tablets, but smaller) doesn't create backpressure, so a PVB would be okay. But you do pay more for a water-soluble fertilizer, compared to what you can use with a spreader. Consider this a convenience thing, or an interesting gadget.

Your spreader-applied treatments don't have to be absolutely positively one hundred percent water soluble. You can also apply weed killers and grub killers, and confine them to the lawn areas, as opposed to flowerbeds and vegetable gardens. Strictly for the money, I doubt you save with sprinkler system fertilizing, even if the equipment was free.

Most sprinkler systems are not anywhere close to 'near-perfect' - even a layout from a textbook becomes imperfect once a tree gets in the way. You could visit the various sites for in-sprinkler fertilizing, and get the information you need to run your own calculations for yearly costs.

RPZ's are not always necessary for a fertigation device. Check you local codes before you install an RPZ. In most states a PVB is adequate for a fertigation device.

Most residential fertigation devices do not produce pressure. Especially the systems that operate of existing water pressure.

Fertilizer for fertigation units is generally more expensive, but will produce better results. A person is very fortunate if 20% of the dry fertilizer is used by the plants. Most of the granules will wash away with the first watering. Through fertigation, 95% of the fertilizer dispensed is absorbed.

In addition, fertigation will drastically reduce the amount of labor associated with fertilizing. It is a simple, fill the unit and forget about it for 2 to 8 weeks depending on the system you choose.

Typically most fertigation systems have paid for themselves in the first year. Generally they reduce water consumption up to 30% and virtually eliminate transplant shock. And as an added bonus, you are helping the environment as opposed to causing damage to rivers and streams.

Guru, it depends on the fertigation device. Any device that injects fertilizer under pressure must, repeat must, be isolated from drinking water with a RPZ, because only an RPZ is rated for toxic backpressure.

Now, a venturi type of device, that draws a fertilizer into the waterline, is a different matter, since there is no pump at work, and no backpressure. Then, a PVB would do, as it is rated to protect from toxic backsiphonage.

Boots, the products I am referring to are the most popular in the residential landscape market not commercial "injectors". All of which do not have pumps or produce additional pressure in the line. For example, Fertile Earth, Fertigator, Ez Flo, Strong, etc... The back flow laws have been a serious issue for the fertigation industry and I have personally delt with this issue in over 40 states. Even within a state, the laws can vary, that is why I suggested checking the local codes first. All in all, the majority of these counties require a PVB, not an RPZ. This may not be true for your area, but once again, it differs between counties.

The common misconception is that these systems are injectors. When reviewed by USC, they were classified as proportioners due to the fact that they do not increase the pressure within the irrigation line. However, a commercial injector, such as turf feeding systems, will increase the line pressure through the use of pumps. These systems will require an RPZ in any state or county. I do not think this consumer was interested in a system that costs several thousand dollars.

Backflow regulations are now mostly regional in origin, coming from one or another regional codes. Within that region, a locality might toughen the backflow protection requirements, but they can never loosen them. They do not have that power under the law. Many people will post about their asking about backflow, and getting a local answer that is false. (from a municipal employee who is largely immune from legal repercussions for spreading incorrect information)

Because someone might be reading here about fertilizing their lawn through their sprinkler system, and may be in possession (He11o eBay) of a positive-displacement injector, the possibility of needing an RPZ should never be discounted.