Chapter 18

 Challenges & rewards of greenhouse plants  Materials used for rooting media  Formulating & pasteurizing rooting media  Timing & methods of watering  Fertilizers & amendments common in greenhouse cultures

 Horticulture vastly growing industry  Great reliance on container-growth plants  Ability to start/grow plants in favorable conditions  Match plant preferences to potting media  Greater 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, nematodes  Steam pasteurization  Most used  Pump steam through soil mixture to kill most pathogens  Chemical 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 irrigation  Slow-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