Getting To Know Your Grow Mediums

Getting To Know Your Grow Mediums main image Getting To Know Your Grow Mediums image

Hydroponic Grow Mediums 

There are a few different types of growing mediums that can be used in hydroponics and choosing the right one will depend on the system you plan to use. Here is a list of the most used mediums and the system they are most compatible with.


Coconut fiber, or “coconut coir,” is arguably the most widely-used of hydroponic grow media. Made from the discard outer husks of coconuts, this recycled coconut coir lays claim to the most environmentally-friendly grow medium used in hydroponics. That said, it is also one of the best. Some advantages of coconut fiber include: pH neutral, anti-fungal, retains moisture, slow to decompose, and it provides plenty of aeration for plants rooting system to remain healthy. Not recommended for ebb-and-flow systems. 

A mix of recycled glass and calcium carbonate comprise another popular hydroponics growing medium: Growstones. These are unevenly-shaped (yet not sharp-to-the-touch), lightweight, and porous, making them an effective hydroponic grow medium, providing beneficial moisture and aeration to the root zone. Growstones are not considered a reusable hydroponic grow medium, however. Plant matter tends to remain inside the pores of these stones, which may make them unsafe to reuse in future growing endeavors. All things considered, the inherent properties of growstones make them one of the top choices as a hydroponic grow medium.

Lightweight Expanded Clay Aggregate (L.E.C.A) are more often used in 'ebb & flow' systems, and as a bottom layer to help drainage when using coco fibre..  These pellets are essentially balls of clay – processed at a super-high temperature – to form a highly porous and effective grow medium. They are light-weight, yet heavy enough to provide good support to a plant. LECA are pH-neutral, non-degradable, and release almost no additional nutrients into the water. Being porous and shaped spherically help to maintain a beneficial oxygen to water balance. These clay pebbles are also re-usable, which makes them an economical hydroponic grow medium for years to come. Note that LECA tends to drain and dry out quickly, and may not be the best choice when used stand-alone in drip systems or wick-type set-ups. Overall these clay pebbles make a great choice for most other hydroponic growing systems. Clay Pebbles are also very popular in DIY Aquaponics Systems.

Rockwool, while once a staple used by almost every 'hobby' grower known to man, has waned in popularity since the advent and continually increasing popularity of coco fibre. 

It is composed of rock (granite or limestone) which is heated, melted, and spun to form long, thin fibers. On the upside, rockwool makes a great seed-starter medium, is porous, sterile, retains moisture, and generally provides similar benefits to other grow media. On the downside, rockwool is non-degradable, which means it essentially lasts forever. Additionally, rockwool has a high pH level and requires soaking before using. The dust from rockwool can be harmful to humans, so caution is advised. That said, Rockwool has a long history in hydroponics, having been an effective and popular grow medium for hydroponic growers for many years.

Perlite and vermiculite are both used to improve moisture retention (Vermiculite) and to improve aeration (Perlite) by mixing through other hydroponic media. A popular and very effective blend is 30% Perlite mixed with 70% coco fibre, and usually available in pre-mixed bags at most good hydroponic retailers. Determining which is better for use in your garden depends on your plants and their needs, and the desired charasteristics of media used.

And they make great liners for outdoor pizza ovens!! (so we're told).



Vermiculite is an aluminum-iron-magnesium silicate that resembles mica in appearance. For use in horticultural applications, vermiculite is heated to expand the particles. This expansion enables it to absorb moisture when used as a potting medium. Vermiculite can soak up 3 to 4 times its volume in water. It also attracts plant nutrients such as potassium, magnesium, calcium and phosphorus. Perlite is an amorphous volcanic rock that is rich in silicon. When mined for use as a potting medium, perlite is crushed and also heated to expand the particles. The microscopic bubbles in perlite granules absorb and hold water as well, but they also hold air.


Vermiculite is a spongy material that is dark brown to golden brown in color. It is shaped like flakes when dry. Perlite is a porous pumice-like material that looks like white granules. Sometimes perlite is mistaken for tiny plastic foam balls when used in potting soil mixtures.


Water Retention

Perlite and vermiculite are both good at retaining water, but vermiculite acts more like a sponge, holding much more water than perlite and offering less aeration for the plant roots. Perlite retains water because of its large surface area with nooks and crannies available for water storage. Because it is porous it allows excess water to drain more readily than vermiculite and improves soil aeration.

Horticultural Uses

Both vermiculite and perlite are used in the garden to prevent soil compaction, improve aeration and retain moisture. They’re also used in propagation of new plants and seed cultivations, as well as in indoor container growing, composting and on lawns. However, the way that each material retains water, and how much water is retained, makes each one suitable for different plants. Vermiculite is ideal for plants that prefer lots of water, such as forget-me-nots and some irises. Perlite would dry out too rapidly for water-loving plants. However, the amount of water vermiculite holds is not ideal for plants such as cacti or rhododendrons, which need a well-drained soil. The moisture retained by vermiculite would lead to root rots or plant death.