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Growing Mediums

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4 Function of Growing Mediums

  1. Anchor and physically support plants
  2. Retain (water holding capacity)
  3. Provide air for gas exchange (porosity)
  4. Nutrient reservoir (CEC)

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Physical Properties

  • Bulk Density: mass of dry soil per unit of volume
  • Porosity: how well the media can retain water and provide air for gas exchange (pore space)
  • Durability: how long will it hold up?

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Chemical Properties

  • Cation Exchange Capacity: determines the ability of a given media to hold on to cations (K+ or Ca+2) aka nutrients
  • pH: measure of the concentration of H+ in the media (pH affects nutrient availability)
  • Electroconductivity (EC): measure of fertilizer salts present

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Growing Mediums Comparison Activity

  • Rockwool
  • Oasis Foam
  • Perlite
  • Sand
  • Gravel
  • Expanded Clay
  • Volcanic Rock
  • Coco Coir
  • Rice Hulls
  • Choose any 2 of the growing mediums from the right on the left
  • Create a Venn Diagram (example below) to compare and contrast your chosen 2 GM on a sheet of copy paper
  • You need to have titles at least 5 points in each of the 3 sections
  • Draw and color a picture of each of the growing medium
  • Resources: This Google Slide Notes and reliable internet sources

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Rockwool

  • Sterile, non-toxic
  • Light weight when dry
  • High water holding capacity
  • No CEC or buffering capacity
  • Ideal for seed germination and long term plant growth
  • Prone to algae growth
  • Not biodegradable

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Oasis Foam

  • Similar to rockwool
  • Popular for ornamental propagation
  • Sterile
  • High water holding capacity
  • Low CEC
  • Brittle damage easily

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Perlite

  • Free-draining
  • Lightweight
  • Sterile
  • No CEC or buffer capacity
  • Creates dust >> potential respiratory irritation
  • Readily available

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Sand

  • Inexpensive
  • High bulk density
  • Low water holding capacity
  • Used as amendment to add weight and improve drainage (depends on grain size)
  • Varying grain size/mineral composition

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Gravel

  • Size: 5 - 15 mm
  • Free draining, good drainage
  • Low water holding capacity
  • High bulk density
  • May require thorough leaching or sterilization
  • Heavy, not easy to work with

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Expanded Clay

  • Free draining
  • Reusable, if sterilized
  • Size: 1 - 18 mm
  • Expensive
  • Mostly used in hobby systems

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Volcanic Rock

  • Mostly used in tropical location for stock plants of ornamental plants (unrooted cutting of poinsettias, geraniums)
  • Used in tropic because available
  • Higher in miner elements
  • Course = drainage but also increased irrigation

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Coco Coir

  • Fiber from coconut husk
  • Sustainable
  • Slow breakdown
  • pH neutral
  • High water holding capacity
  • Can be formed into blocks/slabs
  • Must be leached of Na because grown in coastal area

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Rice Hulls

  • Used in cut flower rose production in South America
  • Naturally occurring: by-product of rice production
  • Added to potting soil to increase pore space and has slightly higher water holding capacity than perlite