Foliar feeding plants can be a very effective means of increasing plant photosynthesis and health.
A combination of a mineral balanced soil, great biology, a plant canopy, and a well designed foliar program can grow a superbly healthy crop, and even help build soil organic matter via root exudates. Foliar feeding acts as a sort of trigger to the plant, with the bulk of the necessary nutrients coming from the soil (and air).
Foliar feeding can help plants absorb particular nutrients at particular stages of growth. For example, calcium is known to help fruit size right after pollination. At this time, a foliar application of calcium with a touch of boron may be helpful.
Foliar recipes require “clean” water. Not many irrigation sources in arid climates have less than the 70 ppm bicarbonates and pH less than 6.5 required for effective foliar recipes. On a small scale and for the best results we prefer using reverse osmosis water, purchasing distilled water, or using rain water. On a larger scale, high pH water can be acidified, which will also remove some bicarbonates. We use this liquid test indicator to measure water pH at home. We use these strips to measure total alkalinity. Multiply the strip alkalinity reading by 1.22 to get bicarbonates in ppm. 1.22 * Alkalinity (as CaCO3 mg/L or ppm) = Bicarbonate (as HCO3 mg/L or ppm).
It is very important to test any source of water other than rain water, distilled water, or reverse osmosis water for alkalinity (which is usually due to bicarbonates when the pH is below 8.3). If the water pH can vary through the season, such as in a stream or shallow well, test it periodically.
Municipal water is usually unsuitable for foliar recipes because of the chlorine or chloramine, usually high pH, and potentially the hardness and bicarbonates. Reverse osmosis alone does not remove chlorine or chloramine, but two stages of activated carbon filtration (found on most reverse osmosis units) will. We have seen a bit of humic acid (in the neighborhood of 1: 1500 or 1:2000) injected into irrigation water remove chloramine using these test strips. Never use water from an ion exchange water softener for foliar recipes – the calcium and magnesium has been replaced with sodium.
The temperature of the water should be 58-78 degrees F; cold water has a harder time dissolving ingredients. If the foliar is used in a grow room or greenhouse, it is especially important the water be at room temperature to avoid shocking the plants. Really, all water applied to plants in a greenhouse should be at room temperature.
Plants must be adequately watered. Do not spray thirsty plants. Nor would you ever fertilize the soil around thirsty plants.
When applying foliars, try to maximize the contact time between the foliar spray and the leaf surface. This means using large droplets, and applying the foliar when humidity is high, so the liquid remains on the leaf surface without drying out. Just adjusting the sprayer for large droplets can make a huge difference.
If the foliar solution runs off the leaves, you have applied too much. The droplets have lost their surface tension, and will not remain in contact with leaves. Likewise, if dew in the evenings makes the droplets coalesce, and drip off the leaves, the foliar feeding will not be as effective as it could have been. Don’t bother to apply a foliar if it is raining or going to rain in a few hours.
Recent studies show that plants do not absorb nutrients through the stomata. The stomata are for absorbing carbon dioxide — often the factor most limiting plant growth. Growing in living soil with good crumb structure facilitates gas exchange; biologically active soil will respire carbon dioxide and increase plant growth.
It is desirable (though often difficult) to apply foliar sprays to both the tops and bottoms of the leaves, thereby maximizing the contact area. My favorite sprayers have a bend at the end of the wand, which makes it easy to get to the underside of the leaves. The undersides of the leaves are shielded from heat and light, and droplets are slower to evaporate.
All foliars need to remain in place long enough to be absorbed. Molasses or spray oils can increase adhesion. High quality fulvic acid like FulPower can help leaf penetration.
The best time to apply foliars is between 3 am and 8 am; this is when plants are growing, and cell division is peaking. The second best time is near dusk in the evening; the droplets will have a good chance of staying in contact with the leaves until morning. Realistically, foliar feeding any time is better than not feeding at all.
The interval between foliar applications can be determined by monitoring the plant’s brix with a refractometer. Generally, the brix will spike 24-36 hours after a foliar application, then slowly drop for the next ten days or so, at which point another foliar can be applied (if practical). We have seen recommendations for applying foliars up to three times per week on high value crops.
Early in the spring the application rate might be 5 gal/acre for vegetables. Later in the season it might be 10-15 gal/acre but the recipe (concentration) of stimulants and nutrients is the same for both seasons. Only the gallons/acre should vary.
Use it or lose it. Do not store any foliar concoction more than 12 hours.
Chelation and Complexing:
Chelated elements are preferred for foliar feeding. When chelated, the molecular element is ringed by organic molecules (often a proteins) which loosely bind it. The ring shields the element from reacting with oxygen, OH- (hydroxides) and/or other compounds, keeping it from forming a tight chemical bond (being “tied up”) and becoming unavailable to the plant.
Sometimes foliars are formulated as “complexes” rather than chelates. This means the elements are connected to the chelating agent, but the element is not completely ringed. The complexes are generally not as resistant to environmental degradation as chelates, however they may be more plant available.
“Chelation refers to a bonding formed between a metal ion (mineral) and a ligand (protein or amino acid chelating agent) carrier. A mineral complex is a mixture consisting of a mineral and an organic compound carrier, such as a protein or polysaccharide; a chelate is a type of complex.” (Reference)
So, all chelates are complexed, but not all complexes are chelates.
Chelated minerals (especially OMRI) are often surrounded by a protein which the plants want to eat anyway.
We sometimes foliar feed one mineral or maybe two at a time as a diagnostic tool. We foliar feed one group of plants, then spray just water on another group. In 24-36 hours we take samples at the same time, crush the leaves with a garlic press, and measure the brix of both groups with a ($25) refractometer. Sometimes we measure the brix of some foliar fed weeds too. If the brix of the foliar fed crop goes up and the brix of the weeds go down you really have something!
We have tried foliar feeding milk in an attempt to slow down a chronic rust problem on garlic. Maybe it did slow down the rust, and it definitely perked up the plants and made them look glossy.
One year we were growing a 2 acre crop of winter squash. It was getting late in the year, and we were worried about powdery mildew. We walked around the perimeter spraying Serenade, an organic fungicide. After a few days we could see that there was no difference between where we sprayed the fungicide and where we did not, so we never had to tread on the plants the field.
If you foliar feed the whole crop you never learn if it is effective. If you maintain a control area, you have the opportunity to measure the results with a refractometer. Just looking at the crop can give you a clue, but if the foliar contained nitrogen, appearances may not match brix readings and nutrient density.
Multi-Foliar feeding involves stacking functions (in the Permaculture sense) where the whole is more than the sum of its parts.
Check with the manufacturer to see if there are any conditions which need to be met when mixing their products. It can be surprising what you learn. Sea-Crop (ocean minerals less the sodium) requires water pH of 7 or more. In general it should not be mixed with anything else, although kelp is ok. Sea Crop is high in magnesium chloride.
The Biomin products are very good, and do require some special blending. For instance, if you want to mix Biomin Zinc, Mg, Iron, Mn, and Cu in one tank, use this ratio: Zn, Fe, and Mn are mixed full strength, in 3X the amount of water. (If you were blending just Zn and Fe, you would use 2X the water.) Cu, apply at 1/3 dilution (add 1/3 the measure of water). Mg is mixed at 3X the strength (add 3X the measure of water again). So, if you were mixing all these in one tank you would have 6.3X the water of just one mineral.
Biomin Calcium is best applied separately, though there are exceptions. You can purchase Biomin factory blended foliars with some calcium in them.
If applying sulfates, keep the total amount to no more than 2 tsp/gallon. Or, increase the water amount for each additional sulfate, as in the Biomin example above. If applying boron, use ¼ tsp/gallon boric acid. Mixing 1:1500 parts fulvic acid into the tank can provide a mild complexing effect.
It is wise to mix a small amount of your recipe, and check if there is any precipitate or milkiness which could clog spray equipment. Beware mixing calcium and phosphorus in the same foliar formula. This is usually a means of producing insoluble calcium phosphate.
Here is how we would concoct a Multi-Foliar Feed:
1) Fill the tank with clean, pH 6.5 water. Fill it almost all the way.
2) Add any pesticides. Usually you would not mix pesticides into a foliar recipe.
3) Add mineral nutrients. We use the Biomin chelated minerals from JH Biotech (Safer) They are more effective than sulfates, and less likely to interact with each other.
Which minerals to try can be based on a paste analysis, a plant sap analysis, or if you are very good at plant communication you will just know what is needed. If there is doubt, maybe reverting to the Diagnostic Foliars is in order.
Mix any pesticides and water soluble nutrients into the full volume of water first. We want those to be as diluted as possible before adding any microbes. Keep the EC below 3.8 mS.
4) Add plant biostimulants. This would be liquid kelp (we like Kelpman from British Columbia), and/or perhaps humic and fulvic acids. Use very little fulvic acid, like a dilution of 1:1500 to 1:2000.
5) Add Microbial biostimulants. Kelp is both a plant and microbial biostimulant.
6) Add Microbial inoculates.
My preference is adding inoculates to the potting soil where I grow transplants, but there are additional benefits to shielding plant leaves with microbes.
It is best to culture biologicals and look at them under a microscope to see if they are alive, before adding them to a spray tank.
When using biologicals. the sooner the application after mixing, the better. Try to keep the time to less than four hours to avoid having the microbes potentially consume each other.
7) If you are using microbial inoculates in a foliar, consider adding a food source like molasses.
8) Add a spreader-sticker. Yucca is the usual choice, but it can be a couple drops of liquid Ivory soap or vegetable oil.
9) Adjust the pH to around 6.5 if necessary. Vinegar will work to acidify the mix.
10) While spraying, keep the nozzle pressure below 65 psi. Living microbes may be damaged at higher spray pressures. Also remember that larger droplets will stay on the leaves longer.
11) When your tank is empty, check the bottom for residue. If you find it, add warm clean water, and go over the area again. Agitating while spraying will help avoid residue. If the mix is high in residue, you can remove the nozzle (orifice) from the sprayer and still get the material onto the soil. Avoid applying high residue materials directly onto plants.
Wendell Owens and Jerry Brunetti recommend mixing orthophosphate into all foliar applications. The triple minus charge of the phosphate will carry the other nutrients into the leaf. They say the phosphate must be in the proper (ortho) form. Orthophosphate can only be used by those not seeking organic certification.
There is an organic approved liquid form of phosphorus. The fish hydrolysate (like from Peaceful Valley or Neptunes Harvest) is stabilized with phosphoric acid. These are great tools for high pH soils, where phosphorus (iron, and other minerals) are unavailable to plants.
We gratefully acknowledge the Acres USA presentations of John Kempf and Wendell Owens and Jerry Brunetti’s writings, and additions from KM Nolan and Don Cox. Much thanks to Franz Fernandez at JH Biotech for help with this document.