Soilless Grow Media for High-Efficiency Systems

The Advantages of Growing in Pumice

Pumice is one of Mother Nature's unique and widely useful creations. Born of earth and fire, pumice is essentially a whipped foam of volcanic glass—each stone made up of highly vesicular strands permeated with tiny air bubbles.

The physical and elemental properties of pumice give it its unique and infinitely useful qualities—qualities that are welcomed in a wide range of industrial and practical applications. That includes horticulture.

Pumice in Horticulture

Pumice is used widely to improve the growability of soils—combating compaction and runoff, improving friability and aeration, and holding moisture and nutrients in the root zone. The same properties that make pumice an excellent soil amendment and conditioner also translate to soilless grow media systems. With the rising popularity of high-efficiency growth systems, especially aquaponic flood-and-drain systems, pumice provides many advantages as a soilless grow media.

Pumice vs. Perlite

Of interest to those familiar with the use of horticultural perlite is a study done by the University of Illinois’ Department of Horticulture that found pumice to be physiochemically analogous to perlite, which translated into similar behaviors and results in horticultural applications. A snippet from the report summary: “It (pumice) proved equally, if not even more effective in some ways, than perlite[1].”

Pumice also provides a greener alternative to perlite and other expanded-to-foamy-usefullness products (see sustainable and green, below).

Why Pumice Excels as a Soilless Grow Media

When considering which grow media to use, these key points should be considered:

Nutrient Holding Capacityan effective grow media must have the ability to retain that nutrient-rich water for a time, making it continuously available to the roots between watering cycles. Ponics Stone™ is entirely made up of pure, natural pumice. This foamed glass stone is riven with countless tiny pores that function as microscopic reservoirs to capture and store nutrient-rich moisture and give it back to the root system as needed. That allows for less frequent watering cycles and avoids problems like algae growth. It also saves energy and reduces wear and tear on the watering system.

The porous, foamy nature of pumice also makes for an ideal environment for beneficial microbes to thrive.

DrainageBalance is so important: a grow media must be able to shed water quickly to allow air into the root zone, yet retain enough nutrient-rich moisture between irrigation cycles to fuel rapid growth. The pores that perforate and pock the sponge-like surface of a Ponics Stone Soilless Grow Media stone are not the same size— and it is this natural variety in pore size, shape, and depth that provide the needed balance for proper drainage. The tiny, microscopic pores hold water and make it available on demand to the root system. The large pores drain quickly, shedding water and taking in air. The hardness and varied shape and size of the stones themselves also prevent compaction of the media.

Gas Exchangea grow media must allow free-flowing exchange of oxygen and carbon dioxide in the root zone. The highly porous, low-bulk nature of Ponics Stone™ facilitates an effective and positive exchange of gases between the root zone and the environment.

Stabilitythe grow media must be substantial enough to support a plant’s root system, as it is the root system that support the plant and the fruit it bears. Pumice grow media is lightweight, yet substantial enough not to float away. The grippy surface of the little pumice stones form a stable bedding matrix to support thriving plants.

WeightGrow beds tend to be positioned above ground/floor level to allow a sump tank underneath and/or to provide easy access when planting and harvesting, and that means grow media weight is an issue. Since pumice is essentially a foamed glass stone, it is less dense and weighty than gravel or sand. 1.5 cubic feet of pumice media weighs 75 pounds. Yet it is weighty enough to stay in place during irrigation cycles.

Crop Balance—As a grow media, pumice provides good drainage, excellent moisture retention, and increased gas exchange necessary for both vegetative and reproductive (fruit) growth.

Media Particle Sizes—Ponics Stone-brand stones are not man-made, but rather natural pumice crushed and screened to the ideal size. Available sizes:

• PONICS STONE™ (3/4" - 5/16") All-purpose soilless grow media for ponic media beds and other growing systems. This pumice stone size blend provides good drainage and germination.

• PONICS STONE™ PREMIUM (5/16" C) Premium Ponics Stone™ demonstrates increased germination rates when sown directly in top-dressed media beds and net pots. This is the ideal media for shallow microgreen beds.

Long LifeTo be able to continually replant in the same grow media saves time and money. Ponics Stone™ is enduring—lasting years in a properly designed and maintained system.

Nutrient Value Contributed by the Grow Media—Ponics Stone™ is more than an inert bedding media, rather, over time, through the activity of microbes, it is slowly mined on a molecular level, contributing valuable nutrients to a ponics system—nutrients like silicon dioxide, iron, ferric oxide, ferrous oxide, sodium, potassium, calcium, magnesium oxide, titanium dioxide.

Sustainable and Green

Since the entire suite of pumice's useful properties are bestowed by nature, the process to prepare pumice for market is simple, sustainable, and green.

Our pumice grow media is not manufactured—it is simply removed from the deposit, crushed, dried, and screened to size.

• No super-heating was necessary, which means lower carbon production emissions than the “expanded” and recycled growing medias on the market.

• No chemicals are used to produce Ponics Stone™.

• No water is needed in the production of Ponics Stone. Even the pumice dust that clings to the particles is useful—providing readily soluble trace minerals and nutrients to the system.

• Hess uses a low-impact, surface mining process to acquire the pumice. The soil (overburden) is set aside and used to reclaim and replant the mined area, returning the land to its natural state of high-desert grassland.


Pumice: An Ideal Soilless Grow Media (PDF)

Ponics Stone Technical Data Sheet (PDF)

[1] Evaluation of Pumice as a Perlite Substitute for Container Soil Physical Amendment. Dianne A. Noland , L. Art Spomer & David J. Williams; Department of Horticulture, University of Illinois, 1201 South Dorner Drive, Urbana, 61801–4720