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