Within the hydroponics industry, there are two main types of feeding regimes: organic and non-organic nutrients. Both these feeding systems pass nutrients into a plant’s vascular system via the roots. There is, however, another way into the plants vascular system. A secret way in.

This secret way is foliar feeding. A commonly overlooked method used in vegetative and flowering stages, foliar feeding allows for nutrients to pass into the vascular system through direct leaf and stem absorption.

Foliar feeding can be a powerful ally to supercharging your plants ready for bumper yields. However, there is a catch. If it is not carried out correctly, it can have such a detrimental effect on your plants that they could be dead within 24 hours.

So, let’s have a look at the dos and don'ts of foliar feeding in the vegetation and flowering stages of your plant's life.

Foliar Feeding: The Don’ts

Don’t Use a Foliar Spray When Your Lights Are On

If you are growing in an environment with a powerful artificial light source, the last thing you would want to do is to cover your plant in a liquid while the light is on. The plant cannot absorb the freshly sprayed liquid fast enough.

The first thing that’s going to happen is that the liquid will act as a lens, amplifying the heat from the lights and burning the leaf. Second, the plant will choke. Usually, when a plant gets too hot, its stomata open to release heat, gas, and water to cool down. However, it will not be able to breathe or self-regulate if the leaf is covered in a liquid that is causing its surface to burn.

Don’t Use a Foliar Spray if it Will be Detrimental to Your Growing Environment

Foliar feeding increases the humidity within the growing environment. While this is great while your plant is in its vegetative stage, it can be a problem when your plant is in flower. During the flowering stage, your humidity is already high. Environment is such an important factor in modern hydroponics that I personally wouldn’t do anything to mess it up.

Don’t Use an Overly Concentrated Foliar Spray

When using a foliar spray, make sure you read the instructions twice and stick to the dilution rates on the label. In fact, I’d even recommend over-diluting the foliar spray just to make sure that you don’t use a mix that could be too strong for your plant (after all, all plants are different).

Foliar Feeding: The Dos

Do Use a Foliar Spray at Lights Out

The best time to use a foliar spray is at lights out. When a plant enters a dark period, its leaves take around 15 minutes to relax. It’s during this time—right after the lights turn off and before the leaves relax—that the stem and leaves are in their most effective absorption period.

Spraying your plant at this point also means that it has the maximum amount of time to absorb the nutrients. If you were to spray your plants too close to lights on, the plant could still be wet when the lights come on. This would have the same negative effects on the plant as if the foliar spray was applied when the lights were on as discussed previously.

Do Use Proper Technique When Foliar Spraying

Cover the plant’s leaves and stem with a light spray. Remember, less is always more as your plants need to absorb all this liquid before the lights come back on. If the leaves are dripping wet, you have used too much. It may take you a few attempts to get it right.

A great tip is to use a foliar sprayer that can be adjusted to expel a fine mist. Again, the finer the mist, the better it will be for the plant to absorb. There are also spray bottles that can be used upside down, which is great for getting into tight spaces and spraying the bottom of leaves.

Do Use Foliar Absorption to Your Advantage

Foliar sprays are a great way to tackle nutrient deficiencies. For example, if your plant starts to show signs of calcium and magnesium deficiency while you are running a nutrient-rich feeding regime, you could look to use a cal-mag foliar spray at lights off every five days to rectify the issue. This way you don’t have to change your standard feeding regime.

This is especially useful if there are multiple plants in your system and only a few are showing signs of a deficiency. The deficient plants can be directly treated with a foliar spray without jeopardizing the other plants feeding schedule.

There is a great range of foliar nutrient feeds out there. Some reduce internode spacing in the vegetative stage by creating more branches, some increase the number of flowering sites while the plant is in the flower stage, and some help with the overall health of your plant by combating deficiencies, pests, and diseases. The list goes on.

So, the next time you grow, consider using the secret way in to help take your plants to the next level.

For further reading, check out The Possibilities and the Realities of Foliar Feeding, which provides a more scientific look at how plant leaves absorb foliar sprays.