Lecture 9A: Container Media

Introduction to Horticulture Lecture 9A

Overview of Lecture 9

  • This lecture is the first in a series of three smaller lectures (9A, 9B, 9C) that cover specialized topics within the subject of soils.

  • Focus on the following concepts:

    • Soilless media and amendments

    • Organic matter contributions to soil

    • Plant nutrition and soil management

  • The week will conclude with a discussion on fertilizers in Lecture 10.

Soilless Media and Amendments

Definition of Soilless Media

  • Soilless media: Anything that can be used as a growing medium without the inclusion of soil.

  • The key function is to provide:

    • Moisture

    • Nutrients

    • Oxygen

    • Suitable growing temperature

    • Structural support for plants.

Characteristics of Soilless Media

  • The mix frequently consists of both organic and inorganic materials including:

    • Organic materials:

    • Composted fir bark

    • Peat moss

    • Forest humus

    • Inorganic materials:

    • Sand

    • LICA (light expanded clay aggregate)

    • Hydroton (expanded clay balls)

  • Some mixes may or may not contain fertilizers.

Soil Amendments

Definitions and Distinctions

  • Amendments: Materials used to improve soil's physical and chemical properties, but are distinct from fertilizers.

  • Fertilizers: Legally defined products that provide nutrients to plants. For example, composted manure is an amendment, but not considered a fertilizer despite having nutrients.

Importance of Soilless Media

  • Advantages of using soilless media include:

    • Lightweight: Easier to handle compared to garden soil.

    • Inexpensive: Generally affordable to produce and obtain.

    • Storage: Easier to store if space allows.

    • Control: Allows for ease in controlling growing conditions and creating customized recipes for various plant needs.

  • Misconceptions around sterility:

    • Most potting mixes and media are not completely sterile. Sterilization can be achieved with various methods but should not be assumed by consumers.

  • Benefits of soilless media versus garden soil:

    • Garden soil can be heavy (70 to 100 pounds per cubic foot) which isn't practical for container gardening.

    • Better aeration, drainage, and regulated moisture retention are associated with soilless mixes.

Composition and Recipes of Soilless Media

  • There are numerous variations and recipes for potting mixes, but all should aim to control:

    • Water

    • Air

    • Nutrients

    • Temperature

    • Structural support

  • A typical mix may include:

    • A combination of various organic materials (like wood products, peat moss, compost) and inorganic materials (like perlite, vermiculite, or sand).

Maintenance of Soilless Media

Characteristics of Fresh Media

  • Fresh potting mixes are desirable for maintaining fertility, low toxins, and consistent particle size which all enhance water holding capacity and drainage.

  • Should generally be used within six months of purchase to ensure optimal performance.

Testing Older Media

  • Methods to evaluate older media include:

    • pH Testing:

    • Ideal media pH usually between 6.5-7.0.

    • Electrical Conductivity (EC):

    • Indicates salt concentrations and overall nutrient availability. Healthy readings generally between 600-1200 parts per million (ppm).

Managing Used Media

  • Used potting mixes can still be effectively utilized by mixing them with garden soil or using as mulch, provided they do not exhibit excessive salinity.

Water Management in Soilless Media

Field Capacity in Container Gardening

  • Container capacity likened to field capacity for natural soil, referring to the volume of water held against gravity after drainage.

  • Different from garden soil due to discontinuity in soil columns in containers, leading to unique watering needs and challenges, such as perched water tables.

Importance of Proper Watering Techniques

  • Techniques like "drain and dump" – where collected runoff from pots is returned to avoid nutrient loss, ensuring thorough hydration of the soil without over-saturation.

Types of Soilless Media Ingredients

Primary Ingredients in Soilless Mixes

  • Notable components:

    • Peat Moss:

    • Harvested from peat bogs and used for its water-holding capabilities while being slightly acidic.

    • Fir Bark:

    • Used often in mixes for non-terrestrial orchids but is gaining traction in tropical plant mixes.

    • Coconut Coir:

    • Eco-friendly and sustainable alternative derived from coconut husks, known for its stability and water retention capabilities but typically incurs high shipping costs.

    • Organic Composts:

    • Examples include mushroom compost, leaf mold, horse manure, etc. ensuring to use well-composted varieties to avoid introducing weed seeds.

  • Inorganic additives include perlite, vermiculite, and sand primarily to enhance aeration and drainage.

Special Considerations

  • Materials like rice hulls and mushroom compost can be used beneficially in moderation.

  • Cautions against common myths in potting, notably regarding the addition of gravel for drainage.

Conclusion

  • Distinguishing between amendments and fertilizers is critical for gardening success.

  • Understanding the roles and nuances of soilless media improves both plant management and soil health.

  • Continuing education through experimentation with various media blends tailored to specific plant needs is encouraged.