Potting-Media Ingredient Research Table

Filter ten container-mix ingredients, compare source-reported properties, or download the research table.

Ingredient properties and sources

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10 ingredients

Potting-media ingredients with source-reported properties and citations
Ingredient	Material and use	Source-reported observations	Limit or caveat
Perlite	Expanded volcanic glass	Purdue reports the ground volcanic ore expands about 4 to 20 times its original volume when heated; it describes the horticultural aggregate as lightweight, porous, and pH 6.5 to 7.5. Purdue Extension HO-255-W Arkansas Extension describes horticultural perlite as a closed-cell aggregate that does not absorb water, so it is used to increase drainage and aeration. University of Arkansas Extension FSA-6097 UF/IFAS lists water-holding capacity as moderate in its hydroponic-media comparison table. This uses a different source/test context from the Arkansas closed-cell description. UF/IFAS EP623	Particle grade and test method matter. Lightweight granules may float during watering; dry perlite is dusty.
Pumice	Porous volcanic rock	Purdue describes horticultural pumice as a light, porous volcanic substrate with pH about 7.0 to 7.4. Purdue Extension HO-255-W UF/IFAS lists pumice as having no CEC, neutral pH, moderate water-holding capacity, and good aeration in its hydroponic-media comparison. UF/IFAS EP623 The ASHS study reports that particle-size distribution changes pumice air/water balance; coarse grades can hold less available water in some containers. ASHS HortTechnology	Do not treat all grades as equivalent. Source and particle-size distribution affect performance.
Vermiculite	Expanded mica mineral	Arkansas Extension describes expanded vermiculite as plate-like and able to hold water and potassium, magnesium, and calcium nutrients. University of Arkansas Extension FSA-6097 UF/IFAS lists vermiculite as having moderate water-holding capacity and good aeration in its hydroponic-media comparison table. UF/IFAS EP623	Source and grade affect pH and retention; avoid compacting wet material.
Sphagnum peat moss	Partly decomposed sphagnum peat	Purdue reports sphagnum peat pH around 3.0 to 4.0 and describes high water- and air-holding capacity for lighter peat grades. Purdue Extension HO-255-W WSU Extension notes that a peat-based mix becomes harder to wet after it dries completely and recommends moistening mix before potting. WSU Extension	Properties vary with decomposition and grade. These are source-specific values, not a universal finished-mix pH.
Coco coir	Coconut fibre	In the named south Florida nursery-substrate trial, coconut fibre retained more water per unit dry weight than the tested pine bark, Florida peat, and prepared mix. UF/IFAS AE562 UF/IFAS lists coir as having high water-holding capacity and good aeration in its hydroponic-media comparison. UF/IFAS EP623	These results describe the tested materials and setup; retail coir products vary. They do not establish one universal coir value.
Composted pine or fir bark	Processed bark aggregate	UF/IFAS lists composted pine bark as high water-holding with good aeration and moderate-to-low CEC in its hydroponic-media comparison. UF/IFAS EP623 Purdue and Arkansas Extension describe bark as a common structural substrate component; bark-heavy mixes are used where aeration and drainage are needed. Purdue Extension HO-255-W	Species, composting, particle size, and age change properties. The row does not claim one recipe suits all plants.
Expanded clay (LECA)	Fired expanded clay aggregate	UF/IFAS lists expanded clay as neutral pH, good aeration, low water-holding, and reusable in its hydroponic-media comparison table. UF/IFAS EP623 Purdue notes lightweight expanded clay aggregate among substrate aggregates used in greenhouse media. Purdue Extension HO-255-W	LECA product and system differ from soil-based potting mix; its inclusion here is for comparison, not a soil recipe recommendation.
Coarse washed sand	Inorganic mineral aggregate	UC Davis advises using coarse, washed sand for media and avoiding beach sand or sand intended for highway de-icing; its root-media notes list bulk density around 100 to 120 lb/ft3. UC Davis Extension UF/IFAS lists sand as low water-holding with good aeration in its hydroponic-media comparison. UF/IFAS EP623	Bulk-density figure is source-reported for sand, not a bag or mix measurement.
Medium horticultural charcoal	Carbonized material	University of Maryland lists medium charcoal as one ingredient in its published orchid-mix example (1 part peat moss, 6 parts fir bark, 1 part charcoal). University of Maryland Extension	The cited extension example documents recipe use, not a universal performance benefit. No general water-holding or nutrient claim is made here.
Worm castings	Earthworm-processed organic matter	LSU AgCenter reports variable NPK values (about 1-0-0 to 5-5-3) and micronutrients; it notes the value depends on feedstock and storage. LSU AgCenter LSU AgCenter describes mixing castings into potting mix and storing them moist but not overly wet, away from ultraviolet light and temperature swings. LSU AgCenter	NPK varies. Castings are not a fixed-dose or replacement-fertilizer recommendation. A commonly repeated percentage was excluded because its primary CSU citation was not verified.

Source values depend on material grade and test method. If a linked source changes or a row needs correction, contact us through the contact form and name the ingredient and source.

Method and corrections

This table reports source observations, not a single tested population. University publications cover different grades, test methods, container heights, and production settings. A value from a nursery-substrate trial is not a guaranteed result in a home pot.

Each CSV row keeps the cited source's context and retrieval date. We do not average values from unlike materials or tests, and blank properties are left out rather than guessed. Derived calculator outputs are kept separate from these observed source notes.

Sources were checked on September 28, 2026. Recheck a source before relying on it for a new recommendation. To flag a broken citation or factual correction, use the contact form and include the ingredient and source title.

The downloadable CSV preserves each source observation as its own row: potting-media ingredient data (CSV).