Greenhouse

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 contd.
• 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
Physical Properties of Media
16
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

• 12 dilution
• 15 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
12 or 15 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)

51
Pour Through

• Volume of water used will depend on the
  container (grower must experiment)
• Collect leachate in tray shortly after
  irrigating
• Filter leachate
• Test pH and EC
• Easy method but few guidelines available,
  although more becoming available. You can
  develop your own guidelines by keeping records
  and being very consistent in your technique.

52
Specific Nutrient Analysis

• Most effectively done by labs.
• Some test kits available for growers.