Your choice of growth media is central to the way you irrigate your plants. Here’s our quick guide to some common, and not so common media to help you know what options are out there.

Jargon Buster

Cation Exchange Capacity – CEC
The ability of a growing media to hold and release positive charged elements (cations). Important nutrient cations include calcium, magnesium, sodium and potassium. Growing media with a low CEC allows cations to be easily leached away whereas growing media with a high CEC withhold cations and act as a long term store.

Air Filled Porosity – AFP
The amount of air space in the growing media.

Water Holding Capacity – WHC
The ability of a growing media to hold and store water.

Coco Fiber (Coir)

What is it? The shredded inner pith of the coconut husk
Where does it come from? Mostly from coconut palms in Sri Lanka and India.
Cost? $13–$50 (3 cu. ft.)
Reusable? Yes
pH: 6.0
CEC: Medium
AFP: Medium
WHC: High
Pros: Naturally contains the beneficial fungus Trichoderma, slowly releases potassium.
Cons: Draws down calcium, easily over-watered.
Irrigation: Manual top-fed, ebb/flow, drip.
Nutrient Requirements: Many growers choose coco coir specific nutrients, others add calcium-magnesium additives.
Usage notes: Coco coir comes in various compressed forms: bricks, bales and slabs. Also available in ready to use loose fill bags.

Coco Chips (Croutons)

What is it? Cube-shaped coconut husk chips
Where does it come from? Mostly from coconut palms in Sri Lanka and India.
How much? Around $65 (3 cu. ft.)
Reusable? Yes
pH: 6.0
CEC: Medium
AFP: High
WHC: Very low
Pros: Naturally contains the beneficial fungus Trichoderma, slowly releases potassium, natural alternative to clay pebbles.
Cons: Tends to float when flooded, needs frequent irrigation.
Irrigation: Ebb/flow, drip
Nutrient Requirements: When using on their own consider incorporating a calcium-magnesium additive to your nutrient regimen.
Usage notes: Excellent for mixing with coco coir fiber to lower the WHC, ideal for using as a mulch on the top of other growing media; excellent for growing orchids.

Vermicrop’s Coco Not

What is it? a soilless medium made from the bark of sustainably harvested redwood trees blended with the fibers of a Kapok fruit
Where does it come from? Mostly California
How much? TBC
Reusable? Yes
pH: Normally 5.5 but increased to a range of 6-7 with oyster flour.
CEC: Low
AFP: Medium
WHC: Low
Pros: Locally made, natural and organic
Cons: Low water retention
Irrigation: Manual top-fed, ebb/flow and DWC
Nutrient Requirements: no special requirements
Usage notes: Does not need to be rinsed but should be fed water only for the first 5-10 days

Perlite

What is it? Superheated and expanded volcanic glass
Where does it come from? Produced worldwide but now mostly in China.
How much? $45 3 cu. ft.)
Reusable? Yes
pH: Neutral
CEC: Low
AFP: High-medium
WHC: Medium
Pros: Lightweight, readily-available, great for rooting cuttings
Cons: Has no buffering qualities, leaches nutrient easily and tends to float when flooded
Irrigation: Manual top-feed, Drip, ebb/flow and aeroponics
Nutrient Requirements: Naturally Inert medium, suits most hydroponic nutrient solutions.
Usage notes: Perlite is available in many grades. 4-12mm is most common for horticulture. Perlite can be used alone or amended into coir, vermiculite, peat moss, or soil mixes to improve aeration/drainage. A 50/50 mix of perlite and vermiculite is ideal for rooting most cuttings.

Vermiculite

What is it? A natural micaceous mineral that expands when heated
Where does it come from? South Africa, China, USA, or Brazil
How much? $40 (3 cu. ft.)
Reusable? Yes
pH: Neutral
CEC: Medium
AFP: Medium-Low
WHC: High
Pros: Lightweight, excellent buffering qualities
Cons: Easily over-watered,
Irrigation: Drip, ebb/flow, and manual top-feed
Nutrient Requirements: Naturally Inert medium, suits most hydroponic nutrient solutions.
Usage notes: Used neat, vermiculite holds too much water for most plants’ needs. Amendment is necessary (see also perlite)

Diatomaceous Earth

What is it? A sedimentary rock made from fossilized remains of diatoms
Where does it come from? Worldwide
How much? $55 (40 litres)
Reusable? Yes
pH: Neutral
CEC: Medium
AFP: High
WHC: Medium-low
Pros: Does not roll, contains silica, sterile (but harbors beneficials well), holds more water than clay pebbles
Cons: Heavy weight; releases sediment
Irrigation: Ebb/flow, drip, DWC, aeroponics
Nutrient Requirements: No special requirements. Diatomite contains silica, which is absorbed into plant tissue and helps improve plant structure and resistance to pests / diseases
Usage notes: Prewash, as sediment may clog drippers. Many growers mix it with hydroton; this makes for improved air / water ratio. Also acts as a good killer of soil dwelling pests.

Sure To Grow

What is it? Recycled polyethylene terepthalate (PET) fibers
Where does it come from? North Carolina (USA)
How much? $60 (9 6”x6” blocks + 3 slabs)
Reusable? Not recommended by the manufacturer
pH: Neutral
CEC: Low
AFP: Medium-High
WHC: High – can hold up to 82% of its total volume when saturated
Pros: Sterile, lightweight, contains no residual particulates, recyclable
Cons: Larger plants will need extra support (i.e., staking / screening)
Irrigation: Top-feed, drip (except waterfarm systems), ebb/flow, DWC, NFT, aeroponics
Nutrient Requirements: Inert medium, suits most hydroponic nutrient solutions.
Usage notes: STG comes in starter cubes, grow blocks, loose-fill cubes, flock, net pot inserts, capillary mats, and starter tray mats.

Rockwool

What is it? Heated basalt rock spun into a fibrous, lightweight material
Where does it come from? Mainly Europe
How much? $80 (9 4”x4” blocks + 3 slabs)
Reusable? No
pH: 8.0
CEC: Low
AFP: Medium
WHC: High
Pros: Lightweight, sterile, recyclable
Cons: Skin irritant, needs pre-treating before use.
Irrigation: Manual top-fed, ebb/flow, drip, DWC, NFT
Nutrient Requirements: Inert medium; requires pre-soaking, suits most hydroponic nutrient solutions.
Usage notes: Presoak with a water and pH Down solution of no less than 5.5 pH. After soaking, allow to drain and irrigate with a suitable nutrient solution before planting. Rockwool comes in starter cubes, plugs, blocks, slabs, mats, and loose-fill (absorbent or repellent granulate).

Clay Pebbles

What is it? Heat-expanded, round-shaped clay pebbles of mixed sizes (8-16mm most commonly used)
Where does it come from? Worldwide, mainly Europe
How much? $70 (100 liters)
Reusable? Yes
pH: Neutral
CEC: Low
AFP: High
WHC: Low
Pros: Difficult to over-water, maintains an excellent air to water ratio when irrigated correctly.
Cons: Bulky, nutrient precipitation on outer surface is common, needs washing before use
Irrigation: ebb/flow, drip, DWC, aeroponics
Nutrient Requirements: Inert medium, suits most hydroponic nutrient solutions.
Usage notes: Spills can be messy. Wash thoroughly before use to remove the small clay particles, this messy sediment may clog pumps and drippers.

Growstones

What is it? Porous rocks made from recycled glass beverage containers received from either the landfill or another source collecting and processing waste glass.
Where does it come from? Santa Fe, NM (USA)
How much? $80 (3.75 cu. ft.)
Reusable? Yes
pH: Neutral
CEC: Low
AFP: High
WHC: Medium-low
Pros: Lightweight; 35% water-holding capacity while maintaining an 85% air-filled porosity; capillary action up to 6″ (15 cm).
Cons: Bulky, needs frequent irrigations.
Irrigation: ebb/flow, DWC, aeroponics.
Nutrient Requirements: Inert medium, suits most hydroponic nutrient solutions.
Usage notes: Wash thoroughly before use to remove small particles. Ideal for using neat or for mixing into coco coir, peat and other growing media.

Peat

What is it? A naturally occuring deposit of partially decomposed vegetation, mainly mosses.
Where does it come from? Peat forms in wetland areas of North America, Ireland, Russia and Northern Europe
How much? Varies
Reusable? Yes
pH: 3.4 to 4.8
CEC: Medium – High
AFP: Medium
WHC: Medium-high
Pros: Readily available,supports beneficials, excellent at holding nutrients and has a good air to water ratio.
Cons: Limited natural resource, extaraction is harmful to the environment, does not re-wet well if left to dry out, naturally acidic.
Irrigation: Manual top-fed, drip
Nutrient Requirements: ‘Soil’ specific nutrients are recommended.
Usage notes: Peat is found in many grow stores in pre-mixed bags or bales. It usually has perlite added for improved drainage, a wetting agent for good re-wetting, and dolomite lime to raise the pH.

SteadyGROW

What is it? Phenolic resin and air
Where does it come from? USA and Canada, out of materials from India
How much? $41 (9 4″x4″ blocks and 3 slabs)
Reusable? Not recommended by manufacturer
pH: 6.0
CEC: Low-medium
AFP: Medium
WHC: High
Pros: No algae growth, sterile
Cons: Reports of phenolic resin’s carcinogenicity by NTP, IARC, and OSHA
Irrigation: Manual top-fed, ebb/flow, DWC, and NFT
Nutrient Requirements: inert medium, suits most hydroponic nutrient solutions.

Usage notes: Comes in two varieties: SteadyGroPro (low water retention) and SteadyGroPro H+ (high water retention)

Water (DWC, NFT)

What is it? Although pebbles may be used to anchor the stem, the plant’s bare roots are in direct contact with an oxygen-rich nutrient solution.
Where does it come from? Good question. Obtain a water analysis.
How much? 0.1 cent per liter for domestic volumes, and 0.03 cents per liter for industrial volumes.
Reusable? Yes (in recalculating systems)
pH: varies; distilled water is 7.0 pH
CEC: N/A
AFP: % of dissolved O2 increases as temperature drops
WHC: N/A
Pros: Readily-available, roots love it when properly aerated and at the correct temperature (64-70F)
Cons: Poor buffering capacity, pH-fickle, may harbor pathogens
Irrigation: DWC, NFT
Nutrient Requirements: inert medium, suits most hydroponic nutrient solutions.
Usage notes: Requires constant aeration to maintain dissolved oxygen levels necessary for healthy roots.

Sand

What is it? a naturally occurring granular material composed of finely divided rock and mineral particles
Where does it come from? Varies
How much? $10-$15 (3 cu/ ft.)
Reusable? Yes
pH: Varies according to its mineral content
CEC: Low
AFP: Low
WHC: Medium
Pros: Cheap, excellent drainage
Cons: heavy, must be irrigated on a schedule for optimal results
Irrigation: manual top-fed, ebb/flow, drip
Nutrient Requirements: Most are inert, some may contain lime. Suits most hydroponic nutrient solutions.
Usage notes: Wash thoroughly before use. Check and correct pH of runoff prior to planting.

Sawdust

What is it? Wood shavings
Where does it come from? Varies, usually as the byproduct of sawmills and retail hardware stores
How much? If you ask nicely, they may give it to you for free!
Reusable? Not recommended
pH: 6.1
CEC: Medium
AFP: Medium-High
WHC: Medium
Pros: Inexpensive, lightweight, biodegradable, harbors beneficials
Cons: pH-fickle, needs frequent irrigations
Irrigation: Manual top-fed, ebb/flow, DWC
Nutrient Requirements: Diligent pH monitoring and adjusting is of the essence. Suits most hydroponic nutrient solutions.
Usage notes: Best used for cycle crops and annuals.

Gravel

What is it? Any loose rock that is larger than 2 mm (0.079 in) in its smallest dimension (about 1/12 of an inch) and no more than 64 mm (2.5 in).
Where does it come from? Worldwide, mostly USA
How much? $12-$15 (3 cu. ft.)
Reusable? Yes
pH: neutral
CEC: Low
AFP: Medium-high
WHC: Low
Pros: Inexpensive, easily-available
Cons: Heavy weight, bulky
Irrigation: Ebb/flow, DWC, Aeroponics
Nutrient Requirements: Mostly inert medium, may contain soluble minerals. Suits most hydroponic nutrient solutions.
Usage notes: Wash thoroughly before use. Gravel is an old school hydroponic substrate.

by Eliab Lozada