Picking the Best Growing Medium for Your Hydroponic System

Hydroponic gardening systems do not require soil to deliver nutrients to plants, but they still require a growing medium. Choosing the right hydroponic growing medium is a crucial step in planning a hydroponic garden, and there are several options available to growers. Growing media must have specific qualities to provide the ideal growing environment, including the ability to support the plant and distribute oxygen and carbon dioxide effectively.

Hydroponic mediums are available at several grow stores, but they are also at www.agron.io. Online stores often offer a greater variety of high-quality hydroponics growing mediums, so growers can be confident in their selection.

Which medium works best for a hydroponic garden depends on which crops are grown and the location, design, and scale of the system. Many gardeners will experiment with different kinds of mediums to find the one that best meets their needs. Below is an overview of the most common types of hydroponic growing mediums.

Soilless Mix Vs. Plugs

Hydroponics growing mediums come in either loose, bulk forms or neat plugs, blocks, or slabs. The loose medium is used to fill bags, buckets, and trays, but many hydroponics growers prefer to use plugs or slabs.

The primary reason for this preference is that seeds can be sown directly into small divots in the plug or slab. As the plant grows, growers can move the plants directly into a larger container without disturbing the plug. Doing this helps prevent plants from experiencing transplant shock.

Some growers will start seeds in plugs, then move them to a larger block once the plant is established. Once the plant outgrows the block, growers will move it to its final pot filled with their preferred soilless mix. Some of the most common soilless mixes are listed below.

Coco Coir

Coco coir, a byproduct of the coconut industry, is made from the husks of coconuts. It is typically sold as plugs, slabs, or blocks, but loose bags can also be found in pet stores and online. Coco coir absorbs an incredible amount of water and holds it for a long period of time, making it perfect for retaining nutrients between irrigation cycles while still providing roots with enough oxygen and carbon dioxide.

Coco coir does not degrade quickly and can be used for several years before replacement is necessary. However, coco coir can contain high salt levels straight from the package. Growers can mitigate this by leeching the coco coir with water before planting. Coir also contains some potassium, so it is recommended to use coco-coir-specific nutrients for plants grown in this medium.

Clay Pellets

Clay pellets, also known as grow rocks, are available in a range of diameters. These rocks contain tiny air pockets that provide excellent drainage and root aeration. Unfortunately, these pellets do not hold water very well, so plants grown in this medium will require frequent irrigation.

Clay pellets are durable and last for several harvests, but diseases are more common in pellets that are reused. Clay pellets can also leach into the water and clog the filters on the irrigation system, so it is important that the pellets are washed well before use.


Growers who use gravel do so because it has excellent drainage, is inexpensive and is widely available. However, it is very heavy compared to other mediums and does not hold water at all. However, it is incredibly useful for those who do not have access to other hydroponic mediums.

Gravel is best used in drip or flood systems rather than ebb-and-flow systems, as ebb-and-flow systems must be used with mediums that can hold water between irrigation cycles. Gravel should also be chemically inert and completely free of lime.


Perlite is a common soil additive, but it can also be used as a hydroponic growing medium on its own. Perlite is a volcanic rock found in lava flows and is available in sizes small enough to start seeds and large enough to support grown plants. Perlite is incredibly lightweight, has excellent moisture-wicking properties, absorbs water well, and provides excellent root aeration.

Perlite does not retain water for very long and dries out quickly between aeration cycles. Additionally, perlite is light enough to float in water, so it is not recommended for use in ebb-and-flow hydroponics systems.


Rockwool is a product made from volcanic rock, coke, and limestone combined at an extremely high temperature. The molten rock is then spun into lightweight fibers similar to the consistency of cotton candy. Once cooler, it is woven into blocks, slabs, or plugs.

Rockwool is completely sterile, has excellent water retention, and perfect root aeration, making it extremely popular among hydroponic growers. Unfortunately, Rockwool is not biodegradable, so proper disposal needs to be arranged. It can be reused several times so long as it is washed well between harvests and there are no issues with plant disease.


Though not the most popular choice, sawdust with a particle size of at least 2mm can be used in hydroponics systems. It also offers excellent water retention, but if the particle size is too small, then inadequate aeration will be an issue.

Sawdust should never come from chemically treated wood. Additionally, growers must never use western cedar, as it is toxic to plants. Wood can sometimes have high amounts of salt picked up in transport from the mill, so salt levels should be tested before planting seeds.

Soilless Mixtures

Soilless mixtures are common, and there are many kinds available at most grow stores, both online and in brick-and-mortar locations. Common components in soilless hydroponics mixtures include peat moss, pine bark, vermiculite, sand, and perlite.

Soilless mixtures are not as long-lasting as some other options and typically break down during the plant’s growing period. Compaction can limit root aeration once the mix starts to break down, so it will need to be replaced periodically. Additionally, many growers avoid using soilless mixes that contain peat moss, as peat moss has a significant negative impact on the bogs from which it is sourced.

Final Thoughts

No matter which medium a grower uses, they should be conscious of the salt levels in their system. Plants do not absorb all the nutrients available to them, which results in a buildup of salts over time. Salts can limit nutrient uptake and harm the plant’s health.

To avoid this buildup, hydroponic growing mediums and the plants’ containers should be flushed with water until the water runs clear. Flushing should be done monthly at the minimum, though many experts recommend doing it weekly.