Growing Media

2. Growing Media Soilless Media, Is it dirt? That is the question

3. Growing Medium • The health and quality of floriculture crops rest largely with the growing medium • GROWING MEDIUM is the material in which plants are grown • In field production or a home garden, soil is the medium. • In greenhouse production, a variety of materials are used as growing media. • Usually soil is not used in the greenhouse.

4. Why is Growing Media So Important? • Growing medium holds water for plant use • Growing medium provides nutrients for the plant • Growing medium permits the exchange of gases to and from the plant roots • Growing medium provides support for the plant

5. Greenhouse Growing Media is Different • Soil that is taken from outside and placed in a pot inside becomes very hard and undesirable for plant growth. • Greenhouses depend upon the media to provide uniform growth in plants. • Greenhouse media is light and easy to ship whereas soil is heavy and would increase the cost of shipping.

6. Desirable Properties of Media • Organic Matter • Bulk Density • Porosity • Aeration • Water Holding Ability • pH • Cat ion Exchange Capacity

7. Organic Matter • Decayed or partially decayed remains of plants and animals • It should remain stable and not break down before the crop is finished • Peat moss and bark are the most common sources of organic matter in growing medium

8. Bulk Density • 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 potted plants • High or heavy bulk density is needed to provide support for plants • Easter lilies need a medium with a high bulk density

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

11. Aeration • The exchange of gases in the medium • Pore spaces that allow air pockets within the medium are vital for healthy root growth • Root cells use oxygen from the pore spaces to convert sugars to energy • This chemical process is known as respiration • A byproduct of respiration is carbon dioxide • It is important that a medium has sufficient pore spaces to allow an exchange of carbon dioxide and oxygen

12. Water-Holding Ability • A growing medium must store water that is available for plant use • AVAILABLE WATER is water that can be absorbed by the plant roots • Available water is found in the pore spaces of the medium • Some water in the medium is considered UNAVAILABLE WATER because it is a thin film of water that binds so tightly on the media particles that it cannot be used by the plant

14. pH • The acidity or alkalinity of the medium is measured as pH • A 14-point scale is used to measure pH • Neutral is 7.0 • 0- 7.0 is Acid • 7.0-14.0 is alkaline or basic

16. pH • The pH is determined by the concentration of hydrogen (H+) ions and hydroxyl (OH-) in the soil solution • A sample of pure water has an equal number of H+ and OH- ions and is therefore neutral • Most essential elements for plant growth are available to most plants when the pH of the soil is between 5.5 and 7.0 • Most plants grow best when the soil pH is between 6.0 and 7.0

18. Cation Exchange Capacity • The measure of a medium’s capacity to hold nutrients • Many nutrients are positively charged cations, such as potassium (K+), Calcium (Ca+2), Magnesium (Mg+), Copper (Cu+), Iron (Fe+3), Manganese (Mn+2), and Zinc (Zn+2)

19. Cation Exchange Capacity • Particles in the medium have negative charged sites • The cations are attracted to these negatively charged sites on medium particles • Cations have the ability to leave a medium particle and be replaced by another cation • This ability to exchange cations is called CATION EXCHANGE CAPACITY

21. Growing Medium Components What’s In That stuff?

22. Soilless Mixes • Most greenhouses today use uniform soilless mixes that are composed of mostly peat moss or bark with perlite and/or vermiculite • Basic components are sterilized to eliminate disease, insect, and weed problems • Nutrients are added and pH is adjusted for optimal plant growth • Soilless mixes can be purchased pre-mixed or you can mix your own

23. Common Components of a Soilless Mix • Peat moss • Coir • Vermiculite • Perlite • Bark • Sand • Plastic foam • Calcined clay • Rock wool • Mineral soil

24. Peat Moss

25. Peat Moss • An organic material dug from peat bogs • Canada, and to a lesser extent, Michigan and Florida are sources of peat for growers in the United States • Canadian peat if very uniform and of high quality • Peat moss has light bulk density, good moisture-holding ability, good air space qualities for the exchange of gases, adequate cation exchange capacity, and a stable pH that is usually between 3.5 and 4.5

26. COIR

27. Coir • Made from waste products of the coconut industry and is therefore considered a renewable resource • Has similar characteristics to peat moss • High water-holding capacity and excellent drainage • Encourages faster rooting of plants • Disadvantage is high salt content because coconuts grow near the sea

28. Vermiculite

29. Vermiculite • A common ingredient in growing media • Origin is a mineral called mica • Mica is heated to 1800o F, which causes it to expand like an accordion • Spaces made by the expansion result in good water-holding ability and aeration • It is very light-weight and can be easily compressed • Has a good cation exchange capacity • Neutral to slightly alkaline pH

30. Perlite

31. Perlite • Originates from volcanic rock • It is crushed, then quickly heated to about 1800o F. The heat causes it to pop like popcorn to form a lightweight aggregate • A good substitute for sand • Stable, sterile, has little cation exchange capacity, has a pH of 7.5 and provides good aeration and drainage • Contains fluoride, which can cause leaf damage to some monocots

32. BARK

33. Bark • From trees • Obtained as a byproduct through the timber industry • Relatively inexpensive • The most widely used is pine • Provides moisture holding ability and aeration • Bark is best next to peat moss as an organic medium

34. PLASTIC BEADS

35. Plastic Foam • Flakes or beads • Styrofoam is the most common • Synthetic polystyrene material • Lightweight and stable • Provides good drainage and aeration • Lacks cation exchange capacity, water holding ability • Neutral pH • Tends to float to the surface of growing media

36. Calcined Clay

37. Calcined clay • Clay aggregate heated to form a hard, stable particle • High bulk density • Improves water drainage and aeration • Has some cation exchange capacity

38. Rock Wool

39. Rock Wool • Human made material from an igneous rock, basalt • Heated to temperatures of 2700o F and once liquefied, is spun into fibers similar in appearance to cotton candy • Used extensively in hydroponics operation • Cubes are used in plant propagation • Granular forms of rock wool are used as a medium component • Good water holding capacity and good aeration • Slightly alkaline • Low cation exchange capacity

40. Sand • Found naturally as a result of weathering rock • Heavy and has a high bulk density that provides solid support for larger plants • Improves drainage and aeration when used with soil • Can actually reduce aeration in peat or bark by filling in pore spaces • pH is between 7.5 and 8.5 • Must be sterilized to destroy disease organisms

41. SOIL

42. Mineral Soil • Obtained from nature as a result of weathered rock • Difficult to find uniform mineral soil with a favorable pH and good structure and texture