Foliar feeding plants can be a very effective means of increasing plant health. However, foliar feeding is not a substitute for soil minerals. Foliar feeding acts as a sort of trigger, with the bulk of the necessary nutrients coming from the soil.
A combination of a mineral balanced soil, great biology, and a plant canopy, a well designed foliar program can grow a superbly healthy crop, and at the same time build soil organic matter via root exudates.
Foliar recipes require “clean” water. This usually means using reverse osmosis water, purchasing distilled water, or using rain water. Very few irrigation sources have less than the 70 ppm alkalinity (or less than 85 ppm bicarbonates if the pH is less than 8) required for effective foliar recipes. It is very important to test any source of water other than rain water, distilled water, or reverse osmosis water for alkalinity. If the source may vary through the season such as a stream or shallow well, test it periodically.
Municipal water is usually unsuitable for a foliar recipe because of the chlorine or chloramine, 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. Never use water from a water softener for foliar recipes – the Ca and Mg has been replaced with sodium.
The temperature of the water should be 58-78 degrees F; cold water has a harder time dissolving the ingredients. If the foliar is used in a grow room or greenhouse, it is especially important the water be at room temperature so as 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 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. This maximizes the contact area. Also, the undersides of the leaves are shielded from heat and light, and droplets are slower to evaporate. My favorite sprayers have a bend at the end of the wand, which makes it easy to get to the underside of the leaves.
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.
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.
If the area is large, 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.
Use it or toss it. Do not store any foliar concoction more than 12 hours.
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 hours or so we take samples at the same time, and measure the brix of both groups with a refractometer. Sometimes we measure the brix of the 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!
Now we are moving toward stacking functions (in the Permaculture sense). Here is how we would concoct a Multi-Foliar Feed:
1) Fill the tank with clean (usually RO or distilled or rain or recently tested) water. Fill it almost all the way.
2) Add any pesticides. This could be something like Neem oil for powdery mildew. Usually you would not mix pesticides into a foliar recipe.
3) Add plant 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. Consult JH Biotech for the total suitable amounts of the Biomin chelates in a mixture.
If using sulfates, keep the total amount to no more than 1 tbsp/gallon. If applying boron, use ¼ tsp/gallon boric acid.
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), or SeaCrop (sea minerals less sodium), and/or perhaps humic and fulvic acids.
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 5.8 using vinegar. pH 5.5 to 6.2 is good enough.
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.
Wendell Owens and Jerry Brunetti recommend mixing orthophosphate into all foliar applications. The double 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.