1. Horticulture Science Lesson 20 Understanding Properties of Growing Media

2. 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.

3. Student Learning Objectives
Define the types of growing media.
Describe the functions of the growing media.
Determine desirable properties of growing media.

4. Terms aeration available water bulk density cation exchange capacity
growing medium
hydroponics
leach
organic matter

5. Terms pH pore spaces porosity soil soilless media unavailable water
water-holding ability

6. 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.

7. What are the types of growing media used in floriculture production?
Soil is the outer portion of the Earth’s crust, which supports plant growth.
In many cases, soilless media or media that contain no soil are used.

8. 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.

9. 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.

10. 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.

11. 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.

12. 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 soil’s fertility as well as improved aeration and water-holding capacity.

13. 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 medium’s bulk density should be light enough to ease handling and heavy enough to support the plant.

14. 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.

15. What are desirable properties of growing media?

16. 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.

17. 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.

18. 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.

19. 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.

20. 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.

21. 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.

22. What are desirable properties of growing media?
Cation exchange capacity is the measure of a media’s capacity to hold nutrients.
1. Many nutrients are positively charged cations, such as Potassium (K+), Calcium (Ca+2), Magnesium (Mg+), Copper (Cu+), Iron (Fe+2 or Fe+3), Manganese (Mn+2), and Zinc (Zn+2).

23. 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.

24. 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.

25. What are desirable properties of growing media?

26. 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.

28. 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.

29. 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?