Yes, a tap water foliar spray works in most cases, as long as your water is fairly soft. The catch is water quality. Mix the same blend in soft water and in hard tap water. The two sprays can behave differently once they hit the leaf. Soft water tends to keep nutrients available. Hard water can leave a chalky film and lower how much the plant takes in.
Good water quality foliar feeding starts before you add nutrients to the tank. Tap water carries minerals. The main two are calcium and magnesium. These minerals decide how soft or hard your water is. Soft water has very little of them. Hard water has a lot. The harder your water, the more those extra minerals get in the way of the spray you mixed up. That is why the same recipe can win in one kitchen and flop in another.
Here is the technical reason. Foliar feeding works because nutrients land on the leaf and pass through the surface into the plant. Dissolved minerals in hard water react with parts of your spray and tie them up before the leaf can absorb them. Some nutrients fall out of solution and turn into bits the plant cannot use. So very hard water does not just dilute your spray. It can lower the strength of the whole mix and waste the nutrients you paid for.
Water pH plays a part too. Most foliar nutrients stay available in the slightly acidic to neutral range, around 5.5 to 7.0. Hard tap water often runs higher than that and pushes the mix in the wrong direction. A mix that sits too high on the pH scale holds onto nutrients instead of releasing them to the leaf. A cheap dropper kit or pH strip checks the tank in under a minute. A splash of citric acid or a buffer brings a high reading back down to range.
Chlorine is the other thing to watch with tap water. Many city supplies add chlorine or chloramine to keep the water clean. These can stress sensitive sprays and the helpful microbes in some organic blends. For those mixes, let the water sit out for 24 hours before you add anything. Chlorine gasses off on its own in that time. Chloramine does not break down as fast. Call your water provider if you are not sure which one your town uses. A small carbon filter on the tap also strips both out if you spray on a tight schedule.
So how soft is soft enough? Practitioner guidance points you toward softer water. Keep the hardness low, since high mineral content reduces uptake. The simplest move is to find out your local water hardness. Many water utilities publish a yearly report with that number. You can also buy a cheap test strip and check it yourself in seconds. Then you can decide if your tap water is fine as is or needs help.
Does your hard water foliar spray keep falling flat? Switch your water source, not your nutrients. Collected rainwater is close to ideal. It is naturally soft and free of the minerals that cause trouble. Set out a clean barrel under a downspout and you will have plenty after one good storm. Softened or filtered water works too when rain is short. Some softeners add sodium, so flush the line before you fill the tank.
The short version is simple. Soft tap water makes a solid base for a spray. Hard tap water drags down your results. You only know which one you have by checking your hardness number. So test first. Let chlorinated water breathe. Keep a rain barrel ready for the times your tap runs too hard. Do that and your sprays land the way you mixed them.
Read the full article: The Truth About Foliar Feeding
