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.

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.

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

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

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.

Chemical Properties of Media 1. pH l measure of the concentration of hydrogen ions (H + ) in media solution lcontrols availability of all essential plant nutrients l soilless (highly organic) media pH l mineral soil pH

Influence of pH and Media Type on essential nutrients

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

Chemical Properties of Media 3. Soluble Salts ldissolved mineral salts found in media lfertilizer, impurities in the irrigation water, organic matter lall nutrients available for absorption are called soluble salts

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

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

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 media 1 add H 2 O slowly from a known volume until medium is saturated to surface allow to equilibrate for 15 min, add more water if necessary

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

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

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

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

Organic Components Peat §formed by decomposition of bog plants § low bulk density § high CEC § manageable pH § non renewable (at least in human lifespan terms)

Organic Components Peat Peat being ‘harvested’ Processed by: Sieving for uniform size Compressed into uniform size and weight bales

Organic Components Coir § coconut husk, treated as substitute for peat § physical properties similar to peat §pH ~7 §low porosity §inexpensive §lower CEC than peat

Organic Components Bark § improves aeration § inexpensive § hardwood or softwood bark can be used § must be composted § various sizes used, most common are: 1/8” to 3/4”

Organic Components Wood 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’

Organic Components Processed 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

Inorganic Components Sand § Used primarily to increase bulk density § Very porous § Inert (no CEC properties)

Inorganic Components Perlite § from volcanic rock § low CEC, inert § good drainage § neutral (in terms of pH §may contain fluoride ions (F)

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

Inorganic Components Rock wool § From basalt rock or slag liquefied and spun into fibers §high total porosity, air space, and water holding capacity § low CEC §neutral pH

Inorganic Components Calcined Clay § Fired clay aggregates § Increases drainage and air space §Minimal CEC §Low bulk density

Inorganic Components Styrofoam § Polystyrene foam § Improves aeration and drainage § No CEC § No water holding capacity § Broken down by UV light § Environmental Nuisance

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)

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

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

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

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.

Mixing Options §Considerations: lmixing equipment ltransportation costs lraw materials lskilled labor lstorage lconsequences of mixing errors lquality control testing

Hoppers for Custom Mixing Media

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.

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

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

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

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

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

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

Determining pH and Soluble Salt Media 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

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 H 2 O § Mix well & equilibrate (15-30 min) § Gravity filter through coarse filter paper § Test pH and EC

Saturated Media Extract §Starting water content does not matter §Starting media amount does not matter §Add deionized or distilled H 2 O 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)

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.

Specific Nutrient Analysis §Most effectively done by labs. §Some test kits available for growers.