PP_lecture 2_media_2025 (2)

Common Names: Medium/media, propagation mix/media, potting soil, soilless mix, substrate.
It is important to note that "dirt" is not an appropriate term for propagation media.

Support: Holds cutting or seed in place during propagation.
Aeration: Allows oxygen to reach the root zone, enabling healthy growth.
Moisture and Nutrient Retention: Needs to balance air and water to retain sufficient moisture while allowing drainage.
Nutrient Retention: Holds essential nutrients for plant growth.

A single medium can meet diverse needs by utilizing a mixture of several components, each imparting unique properties to the mix.

Porosity: Should be porous and well-drained but still retain water.
Composition: Ideally consists of 50% solid particles and 50% pore space.
Soluble Salts: Must be low in soluble salts to prevent toxicity.
Uniformity: Should be uniform in texture.
Sterility: Must be clean, free of diseases, pests, weed seeds, and harmful chemicals.
Decomposition: Should be slow to decompose.
Soilless: Preferably soilless for optimal growth conditions.

Made from partially decomposed marsh or bog plants, serving as the bulk component of most propagation mixes.
Properties:
- Low bulk density, making it lightweight.
- Hydrophobic when dry, leading to increased water retention and nutrient capacity.
- Considered clean due to its acidic pH (as low as 3).
- Percentage of peat in the mix should decrease as container size increases.

Sourced from loblolly, longleaf, and other pine species; a byproduct of the timber industry.
Properties:
- Hammer milled and screened with a mix of particle sizes.
- Improves drainage and increases water holding capacity.
- Percentage of bark should increase as container size increases.

Made from coconut husk fiber; a byproduct of the coconut industry.
Properties:
- Similar properties to peat, with a higher pH (5-7).
- Commonly used to replace a portion of peat (10-50%).
- Potential issues include higher salt and chlorine levels.

Derived from volcanic rock that is crushed and heated.
Properties:
- Holds water on the surface while increasing drainage/aeration.
- Lightweight with low bulk density.
- Stable and inert; different grades based on particle size.

A mica mineral that expands when heated.
Properties:
- Excellent for water retention and nutrient holding.
- Lightweight and low bulk density.
- Structure can be easily destroyed; available in different grades based on particle size.

Used to increase bulk density and water retention in bark-based substrates.
Properties:
- Fills pore spaces to retain water but decreases aeration.
- Not commonly used; should make up less than 10% of the mix if included.

Wetting Agent: Helps hydrate dry peat and aids rewetting if plants dry out.
Limestone: Raises pH to closer to neutral (5.5-6.5) to improve nutrient availability.

A combination of components is essential for desired properties.
Common Mix Ratios:
- 3 parts peat / 1 part perlite / 1 part vermiculite.
- 2 parts peat / 1 part perlite.
- 1 part peat / 1 part perlite for optimal water retention and drainage.

Available in various forms:
- Loose fill bags (2.8 cu ft, approximately 30-50 lbs).
- Small compressed bales (3.8 cu ft, approximately 75 lbs).
- Large compressed bales (100+ cu ft, approximately 2,000+ lbs).
- Bulk loose fill loads, often delivered by dump truck.

Options include wood substrate, recycled cardboard (PittMoss), rice hulls, and peanut hulls.
These components may not be as common as traditional ones and can offer regional specificity in availability.

Examples include Rockwool, Oasis Rootcubes, Oasis Terra Plug, and various phenolic foam plugs.