Foliar Feeding and Fertilization in Hydroponics

When thinking of hydroponic nutrients, it's easy to imagine that the only way to feed your plants is to provide their roots with a nutrient solution that is carefully calibrated and monitored. While this is the default best option as a plant's root system is the most efficient part of the plant at nutrient uptake, it isn't the only way.

If your plants are stressed, or their roots are damaged or diseased, it may be time to look into foliar feeding.

Foliar Feeding

Providing nutrients to a plant through the foliage or vegetation of the plant instead of the root system

Foliar feeding gives you more flexibility when it comes to feeding your plants, as well as the option to more effectively solve nutrient deficiencies.

The Many Benefits of Foliar Feeding

When growing hydroponically, it can be hard for a plant to absorb some nutrients in the root zone. Even if you're calibrating your reservoir, measuring your pH, EC/PPM, and water level appropriately, it's still possible for your plants to run into nutrient deficiency issues.

This can happen for many reasons:

  • Nutrient depletion - one specific nutrient being used up in your reservoir
  • Elements 'dropping out' of the solution by becoming a solid
  • Imbalances in nutrient combination
  • Improper pH levels leading to nutrient lockout
  • Reservoir temperature inhibiting nutrient uptake
  • Nutrient solution deficient in oxygen decreasing nutrient absorption

On top of environmental and nutrient reservoir issues, there are also issues involving the health of your plant's root system. If the roots are damaged, root-bound, or diseased, then they will be much less effective at nutrient absorption.

The list continues to go on:

  • Stressed plants due to improper temperature, humidity, light, density, or radiation levels
  • Pests or disease

Because the list of issues that can go wrong in a hydroponic system are so long, it can take you a while before you figure out:

  1. That a problem is ocurring in the first place, and
  2. Exactly what that problem is.

This is what makes foliar feeding such an attractive option for hydroponic gardeners. Because it is difficult to control for every single variable in a growing system, you can use a foliar fertilizer as a way to hedge against any of the many issues listed above.

How Foliar Fertilization Works

You can think of a leaf as analogous to human skin. We have pores on our skin, and leaves have stomata. These stomata serve a variety of functions, like releasing water vapor in a process known as stomatal transpiration. But they can also absorb water...and the many nutrients that may be dissolved within that water.

A plant's stomata, the vessels that make foliar feeding work!

A plant's stomata, the vessels that make foliar feeding work! source

While plants can absorb nutrition via their leaves, it shouldn't be the only way you feed your plants. The leaves are limited in their capacity to absorb and use nutrients, so foliar feeding is best used as a way to give your plants a quick hit of essential micro-nutrients that they may not be getting via their root system.

How to Apply Foliar Fertilizers To Your Plants

No matter what type of foliar fertilizer you buy, its effectiveness will be limited by how well the leaves of your plants can absorb and transport it. There are a ton of factors that go into how well a plant's leaves can uptake nutrients, only some of which are fully understood.

Because it's nearly impossible to control for all of the factors that affect foliar nutrient uptake, it's best to focus on the essential few that make a huge difference.

Number one on that list would be to use a non-ionic sticking spray. In English, a non-ionic sticking spray is basically something that prevents your foliar spray from beading up on the leaves and rolling off. It breaks the surface tension of the spray and lets it completely cover a leaf's surface, leading to better nutrient uptake.

Pressurized Plant Mister for Foliar Spray

When applying your foliar solution, make sure to use as fine a mist as possible along with your sticking agent so you get complete leaf coverage. Use a pressurized plant mister to get the job done.

Here are simple steps for applying foliar fertilizer to your plants:

  • Apply in early morning or early evening (do not apply in times of high heat and light)
  • Mix your non-ionic surfactant (sticking spray) with your foliar fertilizer
  • Add to your pressurized plant mister
  • Apply to your plants leaves in a fine mist until the solution begins to run off of the leaves
  • Check to see if leaf surface is completely covered

You can continue to foliar feed your plants on a weekly basis, or you can opt to only foliar feed when you notice a specific need. For example, when a plant is transitioning into its fruiting phase or is in seedling phase, you may want to supplement with a foliar application.

Another key time to consider foliar application is when your plants' roots are having a hard time with nutrient uptake in the root zone, AND they require a lot of nutrition because they're in a vigorous grown phase. If you apply foliar fertilizer during one of these times, you're likely to get fantastic results.

Make Foliar Fertilizing Part Of Your Gardening Routine

While your nutrient reservoir will always be the most important source of nutrition for your plants, you should add foliar fertilization to your arsenal of plant care techniques. Study after study has shown that hydroponic plants treated with a foliar spray had a sizeable increase in yield vs. the same crop that wasn't treated with a foliar spray.

So while one of the main reasons to feed your plants via foliar application is to quickly fix any nutrient issues you see cropping up, it will also help boost your yield from otherwise healthy plants!

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