What is The Best Hydroponic Growing Medium? 5 Factors

There are countless hydroponic growing mediums. But how do you choose one? The first time I bought a growing medium for hydroponics, I did not ask any questions, I just placed my order, and I was not able to see a single sprout grow in my seedling tray. It was a failure. Choosing the right medium requires considering a few factors, so do not buy yet..

To choose a hydroponic medium it is necessary to consider 1) water holding capability, 2) porosity, 3) pH 4) particle size and 5) plant height. This is because the hydroponic growing medium must be compatible with the specific plant and hydroponic system.

When I started to ask questions, I discovered the best options based on my growing purpose, what my garden needs, and how it can elevate my harvest of veggies and herbs. If that sounded awesome, let us continue this conversation below.

How to Choose Your Hydroponic Growing Medium?

Before buying a hydroponic growing medium, decide on the plant and hydroponic system first. Identifying these compatibility measures is the determining factor to narrow down possible choices.

Various hydroponic growing media have different characteristics. Some have higher pH, water-holding capacity, and porosity. While, others are cheaper and easier to use. Now, it is all up to you to weigh which is better depending on your hydroponic system and plant.

The most common hydroponic growing mediums are:

• Coco Coir
• Clay Pebbles
• Gravel
• Growstones
• Peat Moss
• Perlite
• Pumice
• Rice Hull
• Rockwool
• Vermiculite
• Wood Chips
• Zeolite

Criteria to Choose the Best Hydroponic Growing Medium

Considering physical properties such as water-holding capacity, porosity, and pH are most vital in relation to the growth of hydroponic vegetables or herbs.

To easily give you an overview, we have summarized different hydroponic growing mediums in terms of these physical properties.

Growing Medium	High water-holding capacity?	High porosity and aeration?	pH neutral?
Coco coir	Yes	Yes	Yes
Clay pebbles	No	Yes	Yes
Gravel	No	Yes	No, limestone can be present
Growstones	Yes	Yes	Yes
Peat moss	Yes	Yes	No, some are slightly acidic
Perlite	Yes	Yes	Yes
Pumice	Yes	Yes	Yes
Rice hull	Yes	Yes	Yes
Rockwool	Yes	Yes	Yes
Vermiculite	Yes	Yes	Yes
Wood chips	Yes	Yes	No, it is acidic
Zeolite	Yes	Yes	No, they are available in acidic and basic forms

1. Water Holding Capacity

Passive hydroponic systems should not use a growing medium with high water retention capability like coco coir.

This property must be associated with the type of hydroponic system. For instance, Kratky hydroponics and DWC will not strictly require a growing medium with high water retention. Why? Because the roots are already soaked in water!

What will happen, you may ask. When a passive system is partnered with a high water holding growing medium, you increase the risk of root rot and algae development. Remember, these organisms like high moisture, low oxygen, and stagnancy.

Other bad growing mediums for passive hydroponic systems are peat moss and wood chips.

2. Porosity

Growing medium should be porous to allow respiration, especially in passive systems where no air pumps are present.

Air is also important for the roots of any hydroponic plant. Your plants also breathe! Science calls it cellular respiration. Considering this, providing a growing medium with spaces gives your plant a healthy space to manage its air and water needs.

3. pH

Hydroponic growing medium can alter the hydroponic pH of the nutrient solution. Acid zeolite is harmful if placed to an hydroponic system with an acid nutrient solution.

Surprisingly, we have a growing medium that can adjust pH. Studies revealed that zeolite can act as a buffering agent that eradicates harmful ions. When we say buffering agent, they can shift the pH from being acidic to alkaline, vice versa.

This is the reason why if you will go back to the table above, zeolite is available in acidic and basic forms. This information becomes handy if your hydroponic nutrient solution is too acidic or basic.

4. Particle Size

Growing mediums may come in big and circular forms like clay pebbles; while others are fine like coco peat. In active systems with big air pumps, using clay pebbles is not advised as these can be sucked by hoses and damage the pump.

The quick draining mechanism of clay pebbles makes them unfit for nutrient film technique (NFT) systems. Why? Because this hydroponic system circulates nutrient water. If the nutrient water cannot hang on to the clay pebbles then the plant will not get enough nutrients and can further die.

Clay pebbles are compatible with deep water culture (DWC) where the roots are submerged for a long period of time. Another example is gravel which does not hold water well. With this characteristic, it is more fit for flood and drain systems.

On the contrary, there are also growing mediums that retain water well like perlite, peat moss, and wood chips. These hydroponic growing mediums are compatible.

5. Plant Height

Accounting for the plant height is key in choosing the right hydroponic growing medium. The best growing medium for lettuce might not be optimum for growing tomatoes. Projected plant height and anchorage are specific factors to consider.

Imagine growing tall tomato plants in rockwool. Do these two elements fit? Absolutely no! Rockwool is often being used in leafy vegetables such as lettuce, bok choy, and kale because they have a rosette growth pattern. This specific growth pattern balances crop anchorage itself, thus a small growing medium like rockwool is already sufficient for them.

On the other hand, tomatoes, peppers, and eggplants need a growing medium that can support their height and stature. Some of the compatible growing mediums for them are clay pebbles, vermiculite, and coco coir.

Full List: Best Hydroponic Medium For Vegetables, Plants and Herbs

Here is a list of the growing mediums we use and recommend for our plants.

Plant	Best Hydroponic Growing Medium
Tomato	Clay pebbles
Jade	Perlite
Kale	Rockwool
Lettuce	Rockwool
Orchid	Clay pebbles
Onion	Coco coir
Zucchini	Clay pebbles
Microgreen	Coco coir
Basil	Rockwool

Do I Need a Hydroponic Grow Medium That Heightens Quality?

The presence of essential nutrients in some hydroponic growing mediums must be taken advantage of. However, choosing these depends on the growing purpose, for instance, harvesting fruits.

Wood chips are known to contain relevant amounts of nitrogen and carbon, which are macronutrients needed by our plants for growth and development.

Zeolite is another fantastic example! Scientific research has proven its ability to prevent plant diseases and disorders such as the blossom end rot in tomatoes. Reduction of the disease incidence resulted in higher harvest.

However, if your hydroponic growing medium does not have nutrients in it, do not be disheartened. The nutrient solution will be sufficient in its job to nourish your veggies and herbs!

Which Hydroponic Grow Medium is More Practical to Use?

Practicality in choosing hydroponic growing mediums encapsulates better options price-wise, easy and clean utilization, and reusability.

Cheap Options

Coco coir, vermiculite, and wood chips are the cheap choices to use as a hydroponic growing medium.

For hydroponic beginners, I highly suggest using coco coir. Not only because of its price but because it is also compatible with the non-complex hydroponic systems like Kratky and DWC, which can be DIY!

Vermiculite is also practical since it is lightweight and is already sterile. On the other hand, wood chips must be sterilized before utilization. That’s an additional step for you, but still worth doing considering its cheap price.

Easier and Cleaner to Work With

For hydroponic garden beginners, working with a clean growing medium might be an issue. Fortunately, coco coir, clay pebbles, gravel, oasis cubes, perlite, rockwool, and vermiculite are all clean growing media to work with.

Reusability

Investing in a reusable growing medium is a wise choice. Clay pebbles, gravel, growstones, perlite, and vermiculite are options with this characteristic.

But, reusing them requires cleaning. This step will ensure that no disease from fungi and bacteria will be present when you start your next growing season.

Cleaning Reusable Hydroponic Growing Mediums

Hot tap water or food-grade hydrogen peroxide can be used to clean used hydroponic growing mediums.

The first step is to make sure that all plant debris is removed from the growing mediums. If you are using hot tap water, you need to submerge the growing medium and mix it. Rinse them, and repeat this process for two to three more times.

If you are using hydrogen peroxide, dilute it first by adding 2-3 teaspoons of it per gallon. Afterward, fill a large bucket with this solution. Place the pebbles, stir them around, and let it soak for 15 minutes. Lastly, strain and rinse them well.

Properly Cleaning Growing Media: Semi-Hydroponics

Sources

• “Basic characteristics of media for container-grown plants” by McCall, W.W. in University of Hawaii
• “Comparison of the use of zeolite and perlite as substrate for crisp-head lettuce” by Ongun, A.R. et al. in Scientia Horticulturae
• “Compost Chemistry” by Cornell Waste Management Institute in Cornell University
• “Improvement of Hydroponic Culture Medium by Adding Calcium-Zeolite” by Fukuyama, T in Acta Horticulturae
• “Measuring a medium’s airspace and water holding capacity” by Gessert, G. in Oregon State University
• “Soil pH in the Home Garden” by Hannan J. in Iowa State University Extension and Outreach