Monday, September 17, 2007

MODULE 6 - Root Substrate and Root Substrate Pasteurization - DUE Tues, Oct. 2nd

Vermiculite, Pine Bark, Perlite, and Sand.

In the past soil or soil mixes were commonly used in greenhouse production. However, the difficulty, expense, and sustainability issues of dealing with soil have lead to the almost exclusive use of soilless media mixes for greenhouse production. There are some important exceptions such as organic in-ground tomato production and cut flower production, but in general if you go to work for a greenhouse you can expect to see soilless media being used. Soilless mixes are more uniform, lighter to ship, and perhaps most importantly sterile and free of disease. This module introduces you to different types of media that are used in greenhouse production both current and historical. You will also learn about the properties of this media. This module requires mostly reading and learning some new vocabulary. It is relatively short, but will build the foundation required for some more intense modules in upcoming weeks.

  • Describe the uses of soil and soilless media in the greenhouse industry
  • Review proportions of solids, water, and gases in soils
  • List the functions of soilless media an soil used as root substrates
  • List and describe the common materials used to produce soilless media
  • Familiarize yourself with the vocabulary of root substrates
hardwood bark
softwood bark
plant nutrients
growing medium
peat moss
sphagnum moss peat
peat bogs
rock wool
fine texture
C:N Ratio
bulk density
polystyrene foam
medium texture
coarse texture

  1. Chapter 6. Root Substrate. pages 197-236

  2. Chapter 7. Root Substrate Pasteurization. pages 237-256

  3. Review Media (PDF of PPT) File from Colorado State (this will be a good review AFTER reading the chapter)

  1. Review Slide Show Introducing Root Substrates (shown below)

  2. Go to the Greenhouse Digital Repository and search the images using 'Root Substrate', choose 5 images of interest to you and describe how the image relates to the material covered in this module. (20 pts)

  1. What are the functions of any root substrate? (soil-based or soilless) (4 pts).

  2. Why are soil-based root-substrates rarely used in the greenhouse industry today? (6 pts, answer in complete sentences)

  3. Explain in your own words how root substrate texture is related to plant water availability and aeration (6 pts, answer in complete sentences).

  4. In number 3, how does the relationship you describe manifest itself into greenhouse management where different sizes and shapes of pots must often be used. (4 pts)

  5. Design a table of desirable root substrate properties. For each property describe the optimum condition and quantitative recommendations when available (i.e., in the case of pH give a common recommended range of values) (15 pts, you can create a table or create a spreadsheet for this exercise).

  6. Based on available water alone which root substrate would be the best for a greenhouse crop and which would be the least preferable? (4 pts, Table 6-1 of textbook).

  7. Produce a graph of %Water and %Air available in 8,6, and 4 inch pots filled with a media made from 1 peat moss: 1 vermiculite (Table 6-2). What physiological process can be impacted by decreased air availability to the roots. (10 pts)

  8. In the first video following the questions the business produces all their own media. What are some of the challenges associated with custom producing your own root substrate? (6 pts)

  9. In the second video, a greenhouse tomato producer uses compost as a regular amendment. What are some benefits and potential hazards of this practice? (5 pts)

  10. Discuss reasons why coir use in the greenhouse industry has increased greatly in recent years. (Answer in complete sentences, 5 pts).

  11. You are growing 5,000 poinsettias for the holiday market. You are producing 'Prestige Red' in 6" standards. How many cubic feet of media will be required? (5 pts, show your work).

  12. In a special native plant project you have made the highly unusual decision to use soil. You heat the soil up to 185 F, but are still having unacceptable losses due to disease. Hypothesize what your problem might be. (5 pts).

  13. Methyl bromide at one time was the chemical pasteurization agent of choice. Explain why its used is being phased out and discuss some alternatives (5 pts).
Locate a picture of an automated root substrate process utilized in the greenhouse industry. Briefly describe how this could be of economic benefit to the business using it.

Monday, September 10, 2007

MODULE 5 - Environmental Controls and Basic Plant Biology - Due Tuesday, September 25th

Tomatoes being produced in a simple, but profitable High Tunnel. Dr. Lewis Jett is an expert on these types of 'greenhouses'.

This week's module covers the short Environmental Control Chapter in your textbook and a short review of plant biology. This course has no prerequisites, so this review needs to happen somewhere. Hopefully, it will be a review for some of you.

The greenhouse environment is a highly variable one. The level of environmental control is also quite variable. Ranging from the basic control provided by passively ventillating "high tunnels" to banks of computers managing everything from active cooling, heating, CO2, HAF fans, irrigation, and fertilization (like you might see in an operation the magnitude of Eurofresh Farms, Inc.) It is important to realize that what the greenhouse grower is striving to do is use the available environmental controls to maximize plant growth towards horticultural goals.

A high tunnel operator may strive to have organic late season tomatoes available. The growers customers may tolerate certain size variation and blemish issues in order to by an organic product locally. However, an organization like Eurofresh may use every environmental control manipulation at their disposal to produce a uniform high quality blemish free tomato at the same stage of ripeness. They may have a delivery wholesale target price and volume that they are contracted to meet. In both cases the individuals in charge of growing plants are manipulating the environment to achieve certain results in plant growth.

In order to understand fully the role that environmental control plays in plant development one must have a good foundation in plant biology. There are entire degrees offerred in plant biology, so the task of packaging this into a single module is relatively daunting. I have tried to boil down some of the most important factors from your reading, but in order to master this subject you will have to do substantially more reading in the future.

Differentiate between manual controls, step controllers, and automated environmental control
Discuss the advantage of integrated control
Briefly Describe the future of Model-based control
Be able to draw and label a typical plant cell
Learn the differences between meristematic and permanent tissues
ID the various parts of a leaf
ID the various parts of a complete flower

manual controls
on/off switch
dedicated microprocessors
Integrated control
model-based control
primary walls
guard cells
cambial meristem
intercalary meristem
pallisade layer
root hairs


  1. Read Chapter 5. Environmental Control Systems in text. (pgs. 185-196)

  2. Watch Slide show on Environmental Controls. Watch two Eurofresh videos on structure and computers.

  3. Review Animation: Flower anatomy (200.498 Kb)

  4. Review Animation: Plant Transpiration Process (371.266 Kb)

  5. Review Animation: Water and nutrient uptake by roots (168.561 Kb)

  6. Review the components of the plant cell at Cells Alive. It will help you answer the study questions.

  7. If you need a basic review you can try this set of HTML pages on the plant Cell from Wellesley College.

  8. For an excellent review of leaf anatomy and leaf tissue organization review the following page and links at the Molecular Expressions Website.

  9. You should be able to label the basic parts of a plant cell, leaf cross section, and flower.
The animations above were made possible for educational use through the Plant and Soil Sciences eLibrary. Please see credits under each animation for further information.

Short essay (answer in complete sentences)
  1. Compare and contrast on/off switches and step controllers. (10 pts).

  2. What are the advantages of integrated control using computers. Why do you think there are still so many growers who don't use integrated control? (20 pts)

  3. Watch the Eurofresh video on structure again. Summarize how computerized environmental control is so critical to their operation. How do you think computer use has made them more profitable. (15 pts)

  4. Briefly describe the evolution of environmental control in greenhouses. (15 pts)

  5. Describe where a "Speaking Plant fits into the evoloution of computer control (6 pts).

Fill in the blank (2 pts each)
  1. The aboveground light absorbing system of plants is made up of primarily_______________ and sometimes___________________.

  2. The basic units of which all plants and animals are made are ______________.

  3. The small bodies within the cell tha contain cholorphyll are called ______________.

  4. Large groups of cells that act together to perform the same function are known as ______________.

  5. Apical meristems are responsible for an increase in the _____________ of a stem.

  6. The epidermis of the root provides _____________ for the inner plant cells.

  7. A group of cells at the tip of a root is called the root ____________.

  8. Most of the absorption of water and nutrients takes place through the ___________.

  9. Water moves from the roots to the leaves through the vascular tissue called the ____________.

  10. The other vascular tissue is called the ______________.

  11. The point at which a plant will no longer recover from a lack of water is known as the _____________ point.

  12. The process of photosynthesis occurs mainly in the leaf ________________.

  13. A bud that grows in the angle between the petiole and the main stem is called an ___________ bud.

  14. Pores or openings in the leaf where gas exchange takes place from the outer air to the intercellular leaf spaces are called _____________.

  15. The male parts of the flower are a slender stalk called the _______________ and the enlarged part at the end called the ______________ where pollen grains are formed.

  16. The female parts of a flower are the ______________, ________________, and _______________.

  17. The showy, colorful parts of the poinsettia are called ___________

Sunday, September 2, 2007

MODULE 4 - Greenhouse Cooling - DUE Tues. Sept. 18th.

Image Source: Munter's

One of the first considerations for greenhouse cooling is to decide what you will be growing. The necessity for greenhouse cooling may increase depending on the things you plan to grow. Once your greenhouse temperature exceeds 85 degrees F, some plants may be stressed from the excessive heat. Your greenhouse cooling requirements may also depend on the climate you live in. If you live in a cooler climate you may not have a concern with greenhouse cooling until summer arrives. (from The Greenhouse Catalog)

  • Review the basic principles of greenhouse ventilation and cooling.
  • Discuss advantages and disadvantages of different cooling systems
fan and pad
passive cooling
active cooling
winter cooling
summer cooling
Chlorine/Bromine injector
relative humidity
sling psychrometer
light intensity
temperature gradient
exhaust fan

  1. Explain why disease incidence may be higher in a greenhouse with a pad-and-fan cooling system than one with fog cooling? (5 pts)

  2. Why is necessary to have a convection tube for air distribution for active winter cooling systems where you plan to use the cooler outside air on those sunny bright winter days? (5 pts)

  3. When the area of cooling pads needed is calculated by a greenhouse designer the thickness of the cooling pad to be used is important to know. For example when a 6" pad is used only 66% of the total square footage of pads is needed as when 4" thick pads are used. Why is this the case? (5 pts)

  4. How do HAF fans assist with active winter cooling? (5 pts)

  5. Describe the major components of a pad-and-fan cooling system and explain the role of each. (15 pts)

  6. Why is a chlorine/bromine injector important to maximize the functional life of the cooling pads? (5 pts)

  7. Why is water quality much more critical in a fog cooling system than in a pad-and-fan cooling system? (5 pts)

  8. One future system that engineers have suggested would be spraying fog directly into existing pads in pad-and-fan systems. What parts of the system you described in question 5 might you be able to eliminate? (5 pts). Do you think this would eliminate the temperature gradient that exists with current pad-and-fan cooling systems? (5 pts).

  9. Conditions for workers are of greater concern now than ever before. What are two advantages of fog cooling systems for employees that spend long hours in the greenhouse? (10 pts).
Watch Microlecture Cooling 1 Now
Watch Microlecture Cooling 2 Now
  • Watch both microlectures.

  • Review calculations for greenhouse cooling on your own. I expect you to know what factors are important and why? For example the role that light intensity, elevation, and allowable temperature rise play in the greenhouse, but you will not be responsible for the direct calculation in this course.

  • Go to the following website and determine the wetbulb temperature for the following scenarios: (TWB = Wetbulb Temperature at the website) You will have to convert between metric and English units is a great site you should bookmark.
Location, Dry Bulb Temp (F), RH
Tucson, AZ 98 F, 27
Clyde, NC 92 F, 59
Fort Pierce, FL 84 F, 77

Based on what you learned in the microlectures answer the following questions based on the above scenario for July 28th, 2007:
  1. What is the wetbulb temperature for the given dry bulb temperture and RH at each location? (15 points)

  2. If the same greenhouse was constructed at all 3 locations which one could achieve the lowest tempterature given the scenario above if the greenhouses were equipped with pad-and-fan cooling (5 pts).

  3. What would be the lowest temperature possible for the clyde location on this day (correct for pad-and-fan) system? (5 pts)

  4. What would be the lowest temperature possible for the Clyde location and scenario if a fog cooling system was installed? (5 pts)

  5. Explain why the lowest temperature possible at the Fort Pierce and Clyde locations is essentially the same on this particular day with these conditions? Afterall it is 8 F cooler in Fort Pierce due to Ocean breezes. (5 pts)
Switching careers is never easy. See the road one grower took. Watch the 'Starting A New Business'