Let's make sure there aren't any misunderstandings about what foliar feeding can do for your plants. Some folks on You Tube and the web might have you thinking that foliar feeding is a way to grow giant plants in half the time. It's not “magic,” it's not a way to feed your plants when your roots are undersized and not well-developed, and it certainly doesn't measure up to some claims about mega-yields and giant plants. If you are an agricultural scientist, then maybe it is rocket science, but for you and Plain 2 Grow Jim (me), it shouldn't be hard. Remember, I'm cheap and lazy!
Jim, what can foliar feeding do for my plants? It can help your plants achieve full potential once you develop a good technique. Foliar feeding plants is more art than science. It takes trial-and-error to get it to work efficiently. But when you do get it right, your plants could survive their temporary ailments and produce as you expected!
How does foliar feeding work? In some of my videos, I talk about foliar feeding and “stomata.” Without going deeply into plant physiology, stomata are simply microscopic holes in the plant leaves, mostly on the bottom, which open and close at certain times of the day and under other conditions.
The stomata are controlled by “guard” cells which open and close the holes. Most plant leaves have a waxy surface, called a cuticle, that protect them from wind, water, sun, and insects. These holes are a way for moisture, oxygen, carbon dioxide, and nutrients to be exchanged through an otherwise sealed surface.
Some growers, particularly commercial growers, will use foliar feeding on a regular schedule. Others like me do it occasionally or only as needed. If my plants are growing on schedule and appear to have no nutrient issues, then I skip foliar feeding. Why do more work and spend more money if it's not necessary? If I start seeing yellowing bottom leaves or some other ailment (see my blog on leaf deficiency charts), I will check my nutrient solution and roots first (see my blog on pH) and adjust as necessary. If after a few days I don't see an improvement, then I will consider foliar feeding the plants. Why?
Foliar feeding is a fast way to deliver moisture and micro-nutrients to a plant that is under stress. Foliar feeding will not deliver a lot of macro-nutrients to the plant.
Heat stress and restricted root uptake of water and nutrients was my driving force to learn this process a couple of summers ago. I believe my tomatoes and peppers made it through with good yields due to my foliar feeding the plants. Since my reservoirs are small, they couldn't keep up with the demand from the plant during 100 degree (F) days. Foliar feeding the plants delivered water, gases, and nutrients, -also cooling them- until the roots cleared and were ready to do their job again.
“Best practices” result from doing something enough times to get reasonable results. After lots of experimentation, I came up with this basic setup: I use a hand-pumped and pressurized chemical sprayer, made by Flo-Master, with an adjustable spray tip. It holds around 1.75 L of fluid. I mix 1 teaspoon each of General Hydroponics Flora Grow, Flora Bloom, and Flora Micro into well water. I then add 1/2 ounce of 3% hydrogen peroxide (see my blog about hydrogen peroxide) and 40 mg of pulverized plain unbuffered aspirin (salicylic acid; here is my aspirin blog) and then adjust the pH of the mixture. A pH of 5.5 to 6.5 works well for me. I will increase the hydrogen peroxide to one ounce after the first one or two sprayers of fluid.
Adjust the spray tip for a fine droplet dispersal. Spray the top and underside of the leaves until the solution drips off. This mixture is weak enough not to cause leaf “burn,” but try not to spray the leaves in direct sunlight. Most growers recommend spraying early in the morning, right after the sun comes up, or later in the evening after the sun goes down.
Foliar feeding is easy, inexpensive, and just might save your plants during temporary nutrient and water deficiencies. If you mix the solution to around half of the reservoir solution strength then you will almost certainly avoid leaf “burn” and nutrient toxicity. Please remember, however, that 90% of what I do is experimental! Nothing is chiseled on a cave wall!