Horticulture Science Lesson 20 Understanding Properties of Growing Media

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Horticulture Science Lesson 20Understanding
Properties of Growing Media
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Interest Approach
Collect samples of growing media. Some
suggestions are water, sand, peat moss, gravel,
garden soil, potting mix, etc. Have the students
vote on which growing medium would be most
effective for growing plants. Then lead
a discussion on what each sample contains that
allows it to be used as a growing media.
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Student Learning Objectives

• Define the types of growing media.
• Describe the functions of the growing media.
• Determine desirable properties of growing media.

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Terms

• aeration
• available water
• bulk density
• cation exchange capacity
• growing medium
• hydroponics
• leach
• organic matter

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Terms

• pH
• pore spaces
• porosity
• soil
• soilless media
• unavailable water
• water-holding ability

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What are the types of growing media used in
floriculture production?

• The health and quality of horticultural crops
  rest largely with the growing medium.
• The growing medium is the material in which
  plants are grown.
• In field production and the home garden, soil is
  the growing medium.

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What are the types of growing media used in
floriculture production?

• Soil is the outer portion of the Earths crust,
  which supports plant growth.

• In many cases, soilless media or media that
  contain no soil are used.

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What are the types of growing media used in
floriculture production?

• Some greenhouse operations grow plants in a
  nutrient solution without any soil, which is a
  practice known as hydroponics.
• The plants in a hydroponics unit are sometimes
  supported in sand or gravel substrate for
  support.
• However, these materials do not provide any
  nutrients.

• With some hydroponic systems, the roots float in
  the nutrient-rich solution or a nutrient solution
  is sprayed directly onto the roots.

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What are the functions of the growing media?

• Growing medium serves four basic functions for
  plants.
• 1. Growing medium holds water for plant use.
• 2. Growing medium provides nutrients for plant
  growth and development.
• 3. Growing medium permits the exchange of gases
  to and from the plant roots.
• 4. Growing medium provides support for the plant
  by giving roots firm anchorage.

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What are desirable properties of growing media?

• Through research, desirable properties of growing
  medium have been identified.
• Some desirable properties for growing medium
  include organic matter, bulk density, porosity,
  aeration, pH, and cation exchange capacity.

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What are desirable properties of growing media?

• Organic matter is decayed or partially decayed
  remains of plants and animals found in the
  medium.
• The organic matter in the medium must be stable
  and must function throughout the life of the
  crop.

• It should remain stable and not break down
  before the crop is finished.

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What are desirable properties of growing media?

• Peat moss and bark are the most common sources of
  organic matter in growing medium.
• In recent years, a material from coconuts called
  coir has gained wider use.
• Organic matter gives soil its dark color.
• Organic matter contributes to the soils
  fertility as well as improved aeration and
  water-holding capacity.

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What are desirable properties of growing media?

• Bulk density is the ratio of the mass of dry
  solids in a medium to the volume of the medium.
• Light bulk density eases handling and shipping of
  the potted plants.
• High or heavy bulk density is needed to provide
  support for plants.

• For potted plants the growing mediums bulk
  density should be light enough to ease handling
  and heavy enough to support the plant.

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What are desirable properties of growing media?

• The spaces between the solid particles of a
  growing medium are pore spaces.
• A higher percentage of pores or porosity in a
  media results in better water drainage and
  aeration or the exchange of gases.
• Good mineral or garden soils have about 50
  percent pore space.
• Organic media used in greenhouses have between 75
  and 85 percent pore spaces.

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What are desirable properties of growing media?
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What are desirable properties of growing media?

• Aeration is the exchange of gases in the medium.
• Pore spaces that allow air pockets within the
  medium are vital for healthy root growth.
• Cellular respiration conducted in the root cells
  requires oxygen to convert sugars to energy.

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What are desirable properties of growing media?

• A byproduct of this respiration is carbon
  dioxide.
• It is important that a medium has sufficient pore
  spaces to allow an exchange of carbon dioxide and
  oxygen.

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What are desirable properties of growing media?

• For optimal plant growth, a growing medium should
  have good water-holding ability.

• Available water is water that can be absorbed by
  the plant roots.
• Available water is found in the pore spaces of
  the medium.

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What are desirable properties of growing media?

• Some water in the growing medium is considered
  unavailable for plant use.
• Unavailable water is a thin film of water that
  binds so tightly on media particles that it
  cannot be used by plants.

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What are desirable properties of growing media?

• Medium pH plays a large role in the availability
  of nutrients in the medium and is the measure of
  acidity or alkalinity of the medium.
• 1. A 14-point scale is used to measure pH.
• A neutral pH is 7.0.
• Any reading between zero and 7.0 is acid, and a
  solution between 7.0 and 14.0 is said to be
  alkaline or basic.
• The pH is determined by the concentration of
  hydrogen (H) ions and hydroxyl ions (OHB) in the
  soil solution.
• A sample of pure water has an equal number of H
  and OHB ions and is therefore neutral.

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What are desirable properties of growing media?

• 2. Most essential elements for plant growth are
  available to most plants when the soil pH is
  between 5.5 and 7.0.
• If the pH is above or below that range, the
  availability of nutrients may be restricted.

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What are desirable properties of growing media?

• Cation exchange capacity is the measure of a
  medias capacity to hold nutrients.
• 1. Many nutrients are positively charged
  cations, such as Potassium (K), Calcium (Ca2),
  Magnesium (Mg), Copper (Cu), Iron (Fe2 or
  Fe3), Manganese (Mn2), and Zinc (Zn2).

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What are desirable properties of growing media?

• Clay and organic matter particles in the medium
  have negative charged sites.
• The cations are attracted to these negatively
  charged sites on media particles.
• This is the same principle of attraction that
  applies to magnets.

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What are desirable properties of growing media?

• 2. The cations can leave the medium particle and
  be replaced by a cation held in the medium
  solution.
• For instance, a potassium atom may leave the
  particle and be replaced by a copper atom
  dissolved in the soil water.
• This replacement of one cation for another is
  called cation exchange.
• The fertility of a medium is directly related to
  the number of cations a medium can attract and
  hold.
• The greater the cation exchange capacity, the
  greater the fertility of the medium.

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What are desirable properties of growing media?
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What are desirable properties of growing media?

• 3. Nutrients leach or wash out of the medium
  during watering.
• The loss of nutrients requires the grower to
  replace them with fertilizers.

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What are desirable properties of growing media?

• In the greenhouse industry, the growing medium
  must provide conditions that encourage uniform
  plant growth.
• This is because a crop in which all the plants
  have the same rate of growth and development is
  highly valued by customers.
• A uniform growing medium helps to ensure that the
  plants grow at the same rate.

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Review/Summary

• What are the types of growing media used in
  floriculture production?
• What are the functions of the growing media?
• What are desirable properties of growing media?