Greenhouse Growing Media

1. Greenhouse Growing Media

2. Mixing Media Like Making Soup • When first made, each ingredient still easily identified • Eventually chemical and physical properties become blended creating unique characteristics. • Characteristics are chosen to meet specific needs of plants.

3. Functions of Media • Provide water • Supply nutrients • Permit gas exchange • Provide support These functions can be controlled by the grower by choice of component blends.

4. Problems with Sub-Optimal Media • Poor growth • Nutritional disorders • Increased risk of root diseases • Inefficient/ineffective irrigation • Unstable (toppling) plants

5. Rootzone Environment Creating a rootzone environment: • blending selected components • filling pot • initial watering of containers after transplanting

6. Rootzone Environment • Constantly changing as roots grow into medium. • Roots: • Extract nutrients • Exude chemicals such as H+ and phytochemicals • Contribute organic material to the medium.

7. Chemical Properties of Media 1. pH • measure of the concentration of hydrogen ions (H+) in media solution • controls availability of all essential plant nutrients • soilless (highly organic) media pH 5.4-6.0 • mineral soil pH 6.2-6.8

8. Influence of pH and Media Typeon essential nutrients

9. Chemical Properties of Media 2. Cation Exchange Capacity (CEC) • measure of media nutrient holding capacity • defined by sum of exchangeable cations (+ charged nutrients) that media can contain per unit wt.

10. Chemical Properties of Media 3. Soluble Salts • dissolved mineral salts found in media • fertilizer, impurities in the irrigation water, organic matter • all nutrients available for absorption are called soluble salts

11. Physical Properties of Media(Air- and Water-holding Capacity) Determined by: • size and type of solid components • how medium is handled (compaction, amount per pot, watering technique, etc.) prior to planting

12. Physical Properties of Media • Bulk Density- weight per unit volume • Total Porosity- Percent volume of media comprised of pores • Water Holding Capacity- % volume of media filled with water after saturating and draining

13. Determining Physical Properties(approximation method for growers) Method [use metric units (g and cc) throughout] • cover inside of container (must have hole for drainage) with cheese cloth or screen material and cover container hole with tape • fill with a measured volume of media1 • add H2O slowly from a known volume until medium is saturated to surface • allow to equilibrate for 15 min, add more water if necessary

14. Determining Physical Properties(approximation method for growers) Method cont’d. • record vol. of H2O added2(original volume minus remaining volume) • remove tape, collect drained H2O for 60 min, record volume3 • weigh wet sample4, air dry the sample, reweigh5 The measurements recorded from this procedure are then used where indicated by superscript(1,2,3,4,5) in the following formulas:

15. Bulk Density- weight per unit volume 5Mass of dry media (g) 1 Media volume (cc) (to convert to ~pounds/cu. ft., multiply answer by 62.4) Physical Properties of Media

16. Total Porosity - Percent media volume comprised of pores • 2Volume of water added • 1media volume • most mineral soils have less pore space than organic based media x 100 Physical Properties of Media

17. Physical Properties of Media • Water Holding Capacity -% moisture in the media after saturating and draining • (4wet weight - 5dry weight) x 100 • 1media volume • It is the maximum amount of water media can hold

18. Media Components

19. Organic ComponentsPeat • formed by decomposition of bog plants • low bulk density • high CEC • manageable pH • non renewable (at least in human lifespan terms)

20. Organic ComponentsPeat Peat being ‘harvested’ Processed by: • Sieving for uniform size • Compressed into uniform size and weight bales

21. Organic ComponentsCoir • coconut husk, treated as substitute for peat • physical properties similar to peat • pH ~7 • low porosity • inexpensive • lower CEC than peat

22. Organic ComponentsBark • improves aeration • inexpensive • hardwood or softwood bark can be used • must be composted • various sizes used, most common are: 1/8” to 3/4”

23. Organic ComponentsWood Products - sawdust • Inexpensive way to get organic matter into media • Must be composted • Considered too variable for use in commercially available media • Can be too ‘reactive’

24. Organic ComponentsProcessed Sludges and Composts • Sludge - sewage processing by-product • high CEC • high bulk density • little pore space • make-up dependent on starting material, may contain high concentration of heavy metals

25. Inorganic ComponentsSand • Used primarily to increase bulk density • Very porous • Inert (no CEC properties)

26. Inorganic ComponentsPerlite • from volcanic rock • low CEC, inert • good drainage • neutral (in terms of pH • may contain fluoride ions (F)

27. Inorganic ComponentsVermiculite • Aluminum-Iron-Magnesium silicate (mica like) • pH depends on source • High CEC • provide nutrients Ca, Mg, K • great water holding • low bulk density

28. Inorganic ComponentsRock wool • From basalt rock or slag liquefied and spun into fibers • high total porosity, air space, and water holding capacity • low CEC • neutral pH

29. Inorganic ComponentsCalcined Clay • Fired clay aggregates • Increases drainage and air space • Minimal CEC • Low bulk density

30. Inorganic ComponentsStyrofoam • Polystyrene foam • Improves aeration and drainage • No CEC • No water holding capacity • Broken down by UV light • Environmental Nuisance

31. Selection and Storage of Commercially Prepared Media

32. Selecting Media • Important- one size does not fit all • Consider crop needs • What is the optimum growing pH? • What kind of moisture level does it require? • Particle size (germinating seeding vs established plant) (size and type of root system - fine or coarse) • Watering methods (high pressure watering requires a media resistant to compaction and erosion)

33. Trial New Media • Test new product to determine suitability Be sure you have a big enough sample size! • Consider Cost • Quality and quantity of the finished plant are the most important considerations

34. Media Storage • Use within 3 months of production (follow manufacturers recommendation) • If dries out, may be difficult to re-wet • If it gets wet - algae and moss may grow, fungus gnats and shoreflies may infest it. • Store off the ground (on pallets) with good air circulation • Keep out of direct sun

35. Avoid Overhandling • Commercially prepared media are formulated with certain “built-in” aeration and water retention properties • Properties altered when handled by: • potting machines • flat fillers • mixers • untrained human media handlers

36. Formulating and Mixing Media

37. Mixing Options • Can buy commercially prepared media • Can custom mix your own media The choice is up to the grower/owner. In general smaller greenhouses tend to buy while larger tend to mix, but this is not a hard and fast rule.

38. Mixing Options • Considerations: • mixing equipment • transportation costs • raw materials • skilled labor • storage • consequences of mixing errors • quality control testing

39. Hoppers for Custom Mixing Media

40. Soilless Formulations • Whether commercial or mixed on site, most mixes are derived from two groups of media mix formulations established at University of California and Cornell University.

41. Media Formulations • Based on combinations of peat, vermiculite, perlite • Nutritional and other additives depend on the crop

42. Wetting Agents • Non-ionic wetting agent added to improve initial wetting of media mix • Granular and liquid forms • High concentrations toxic to plants • Most commercial mixes contain wetting agents

43. Media Testing

44. Tests • pH, EC, and specific nutrients • pre-plant analysis • amend as necessary • after planting analysis • monitor changes in pH and nutrient accumulation • adjust fertilizer composition accordingly

45. Sampling • Factors to consider when sampling media • number of samples to take • when to take samples relative to fertilization (be consistent) • sampling location with pot or bed

46. Sampling Units • Pooling- mixing small random samples together to form a larger collective sample • potted plants - collect sample from root zone, sample minimum of 10 plants • plugs/cell pack - sample from 5-10 different flats, plants sacrificed • BE CONSISTENT in your sampling method

47. If you are trying to diagnose a problem, include samples from healthy and affected plants in order to compare results.

48. Determining pH and Soluble SaltMedia Extraction Methods • 1:2 dilution* • 1:5 dilution* • Saturated Media Extract (SME)* • Pour-through** It is VERY important when sending soilless media samples to a lab to label them as soilless * Guidelines are available to interpret results ** Few guidelines are available, you have to develop your own

49. 1:2 or 1:5 Dilution • Air dry media • 1/4 - 1/2 cup (50-100cc) media mixed with 2 (or 5) parts deionized or distilled H2O • Mix well & equilibrate (15-30 min) • Gravity filter through coarse filter paper • Test pH and EC

50. Saturated Media Extract • Starting water content does not matter • Starting media amount does not matter • Add deionized or distilled H2O to container of media until media is saturated • Equilibrate (30 min) • Vacuum filter through coarse filter paper and collect leachate • Test EC and pH (can also test pH before filtering)