Chapter 18
Apr 01, 2015
Chapter 18
Challenges & rewards of greenhouse plants
Materials used for rooting mediaFormulating & pasteurizing rooting
mediaTiming & methods of wateringFertilizers & amendments common
in greenhouse cultures
Horticulture vastly growing industryGreat reliance on container-growth
plantsAbility to start/grow plants in
favorable conditions Match plant preferences to potting
mediaGreater ability to manipulate
climate, fertility, water etc.
Soilless culture can yield much higher per acre than soil culture –not realistic Expensive Difficult to manage More consistent aeration, water retention
Important Properties of Root Media Stable organic matter or low C:N Water retention w/ adequate aeration Moderate/high CEC Suitable pH
Stable organic matter Moderately decomposed – don’t want it to
shrink too much decreasing aeration Greenhouse media tends has little
natural fertility, needs ability to retain nutrients
Components of Root Media Mixes Peat moss▪ Decompose slowly▪ High water-holding capacity▪ Can be acidic
Bark▪ Can replace peat moss▪ Less expensive▪ Should be composted
Sawdust, straw, manures▪ Sawdust & straw should be composted 1-2
mos.▪ Manures▪ Used little due to ammonium toxicity▪ Can be good in certain situations
▪ Vermiculite▪ Silicate material▪ High water holding capacity▪ Great aeration▪ High CEC, w/ some K, Ca, Mg
▪ Sand▪ Best drainage & aeration▪ No CEC or nutrient availability▪ May work for starting plants
▪ Perlite▪ Heated volcanic rock▪ Sterile & inert▪ Good substitute for sand
Soil-Based Root Media 1/3 sand, 1/3 peat moss, 1/3 soil Keep clay content low Can make at home/lab w/ ability to sterilize
soil Soilless Root Media
Materials to use▪ Vermiculite, organic matter, sand, perlite,
sphagnum peat moss▪ Can mix yourself, or buy premixed
Pay close attention to fertility management
Pasteurization controls Weed seeds, pathogens, insects,
nematodesSteam pasteurization
Most used Pump steam through soil mixture to kill
most pathogensChemical pasteurization
Cheaper Must allow to aerate after treatment Chemicals are nasty to handle
Methyl bromide ▪ Severely injurious to humans▪ Can be damaging to some plants
Chloropicrin (tear gas)▪ Can’t use where plants are growing
Incorrect watering most frequent cause of reduced crop quality or failure
Watering Guides Use well drained rooting medium Wet entire root media w/ each watering
(till it drips)▪ Leaching can then remove excess soluble salts▪ All root area is wet
Wet before dry stress occurs
Watering Systems Hand▪ Frequency often questionable▪ Quantity inconsistent▪ Plant damage
Automated▪ Sprinklers, drip, microirrigation, water tables
& capillary action▪ More consistent timing, and amount▪ Must have good equipment, proper air flow,
humidity control
Plant Nutrients Vary w/ rooting media & crop May need to pay close attention to
micronutrients▪ May are available as mixtures or can be
incorporated into irrigationSlow-Release Fertilizers
Release over first 3-4 mos▪ Some may be 6-15 mos
Many greenhouse production problems related to soil fertility
Can sample root media (every 3 mos)
Tissue sampling can be done to troubleshoot a problem May be critical in large greenhouse
production operations w/ high value crops
All nutrients must be supplied in solution Can control fertility very specifically Takes specific equipment for metering
Plant support Fixed above, or floating Keep aeration in water, or w/ wool, perlite,
sand▪ Used commonly in research on roots to keep
soil out of way
Root Aeration & Darkness Bubble air Baffles in water flow Keep root system in dark▪ Inhibits algae growth