Tidbits from OFA

The OFA Short Course in Columbus, Ohio, offered a plethora of seminars geared toward growers. We understand that not everybody can make it to the show, so we’re bringing it to you. Here you’ll find summaries of eight of the grower seminars, all written by the presenters themselves. We hope the information will be helpful to you and maybe next year you’ll be able to hear even more by attending in-person.

Understanding the microbial activity of your root media

By Kimberly A. Williams, Kansas State University

While the physical and chemical properties of root media are fairly well understood and applied in greenhouse crop production, the biological properties of soilless mixes are barely on our radar. However, all three properties are components of creating and maintaining a healthy root zone for crops. In fact, a central tenet of sustainable greenhouse production includes fostering a root medium that is “alive” and teeming with beneficial microbial populations. These “good guy” bacteria and fungi are necessary for nutrient cycling and suppression of root diseases.

Through the root medium and our management practices, growers create the environment for microbial populations — it is analogous to their village, if you will. Soilless mixes provide water, oxygen, and food source to bacteria and fungi, and they influence the distribution and variety of microbes that thrive in them. That is, the microfauna is composed of both ‘good guy’ beneficial organisms and ‘bad guy’ pathogenic microbes. And just like in the movie “The Field of Dreams,” “If you build it, they will come.” That is, microbial organisms are ubiquitous and will develop in root media during production. Soilless mixes are not sterile; they are teeming with naturally-present bacteria and fungi. And when we fertilize with organic nutrient sources, these materials also contribute microorganisms — and a food source for them — to our production system. In fact, the plug or rooted cutting that we transplant even brings a dose of (hopefully “good guy”) microbes into the finish container. Suppressing pathogenic, or “bad guy,” microfauna is certainly essential during crop production. Which of the microbe species thrive depends on many factors, many of which are determined through grower management practices.

So is it necessary to treat root media with either commercially-available inoculants or home-brewed compost teas to gain a root environment with a healthy dose of “good guy” microbes? Our recent research at Kansas State University suggests that the answer is “not necessarily.” We 1) have not measured meaningful increases in impatiens shoot growth when commercially-available ‘good guy’ bacterial inoculants and mycorrhizae were applied; and 2) we have measured increased general microbial activity immediately upon application of organic nutrient sources compared to inorganic nutrient sources. However — and this is important — this doesn’t mean that a grower does not want to provide insurance against the village (i.e. the root zone) being pressured by “bad guy” (i.e. pathogenic) microbes — and that is what we do when we incorporate “good guy” microbes like Trichoderma or Bacillus subtilis into our production systems. Using our analogy, think of it this way: we can’t always measure the benefits of the “good guys” presence unless the “bad guys” are present, too, but that doesn’t mean that we don’t want the “good guys” protecting the village, just in case the “bad guys” show up.

Therefore, growers are best off when they build a well-managed village — a root zone that supports microbiological dynamization with appropriate water, oxygen and high quality food sources — and then take out insurance by including “good guy” beneficial microbes early in the cropping cycle in case the ‘bad guy’ pathogens come calling. Because good roots produce good shoots, this attention paid by growers to the biological properties of the root zone yields high quality plants.
 

Tough perennials for tough landscape design

By Rita Randolph, Randolph’s Greenhouses

Not only have I been coming to OFA meetings since I was a teenager, but I grew up in the greenhouses/nursery business and have also been a garden writer and lecturer for years. Continuing education over the years has been crucial to my success in the business of growing plants, and still is. As they say, “You’re never too old to learn,” and in this fast-paced seasonal life, live or die depends on the performance of your plants. Not only do they need to be healthy, grow and bloom, but modern times insist they look good for months at a time.

More and more perennials are being used in the landscape, with annuals used as focal points of intense color. Just as trees and evergreens are known as the “back-bone of the garden,” perennials are the blankets, and turf-grass is the Persian carpet. When the balance of all four comes together, you have a very well-designed garden or installation.

As a grower or retailer, plants should be staged with others they look good with, instead of only offering them alphabetically in rows outside on a black mat. A small area dedicated to displaying them together with their “friends” gives the shopper a clue of how to better use them or gain inspiration from you.

Many times a perennial performs well for a while, then fizzles out, or needs clipping, so companion planting is one way of getting the most out of the plants. Contrasting foliage and flowers with ornamental grasses will help give structure, but combining perennials with sturdy evergreens or bold foliage shrubs provides a stronger contrast in some cases.

An old way of masking seasonal plants was to border them with a short parterre’ or low bordering hedge. That way if the plants were young and immature, or when they needed deadheading, the evergreens stood out. But when the perennials are in bloom, the combination creates a fabulous collar or border. I still see this system used, but a more natural way to design with them is by seeing how they grow in nature too. Simply staging the plants in waves or just the right focal point, as in understory perennial beds, and complementing them with large stone, a wooden fence or some other form of hard-scape items. Ornamentation with rocks and such takes the pressure off certain perennials that do not perform year round.

The toughest perennials are simply the ones that grow well in your area. Plants native to certain parts of the country may not be as adapted to your location, but experimentation is good sometimes and we can be fooled. When choosing ornamental plants that are hybrids or selections, even if they are from other countries, care should be taken that they are from a locale that has similar weather patterns. There are, of course, micro-climates everywhere, and this can be used to great advantage in trying to expand your perennial pallet.

Assuming that the soil has been amended and the plants properly installed, watering is crucial till the plants are established. One day without water when they really need it will cause irreversible stress and damage to the plant, if it survives at all. The best perennials still need to be helped along in their new environment, and occasionally repositioned if it turns out to be too tall, too short, or simply looks out of place. I remember visiting a botanical garden and remarking about how beautiful it was, and how well designed. The horticulturist said, “Are you kidding?! Every plant here has been moved many times to get it to look this way!”
 

New PGR information for greenhouse crops

By Joyce Latimer (Virginia Tech) and Jim Barrett (University of Florida), sponsored by Fine Americas Inc.

We shared the session to provide an update on new uses and research results on the use of plant growth regulators (PGRs) on a variety of greenhouse crops. The session covered both growth retardants and chemical pinchers with specific chemical and use recommendations for specific crops, including herbaceous perennials, annuals, and important potted crops.

The growth retardants are generally considered to be the anti-GA products. These products include ancymidol (Abide, A-Rest), chlormequat chloride (Citadel, Cycocel), daminozide (B-Nine, Dazide), flurprimidol (Topflor), paclobutrazol [Bonzi, Paczol, Piccolo, Piccolo 10 XC, Downsize (drenches only)] and uniconazole (Concise, Sumagic). These products reduce plant growth by inhibiting the biosynthesis of gibberellins (GA), which are the plant hormones that stimulate cell and tissue elongation. Remember these PGRs inhibit plant growth. Therefore, they must be used in conjunction with all the other grower tools employed to produce a high-quality product.

The session included new research results on the chemical pinchers, PGR products that enhance plant branching. These include benzyladenine (Configure), dikegulac sodium (Augeo) and ethephon (Florel). These products all have different modes of action but stimulate plant branching by reducing apical dominance. These products may affect plant growth as well, especially at higher rates.

Joyce described how to use PGRs to improve finished quality of herbaceous perennials with specific recommendations on major crops. For example, several Coreopsis species and cultivars are responsive to Configure to improve branching in both the liner and finished crop stages. Coreopsis is also responsive to all of the growth retardants at moderate rates. Multiple applications at lower rates may result in better finished plant quality. Liner dips provide effective early control of Coreopsis.

Echinacea is also very responsive to Configure, generally doubling the number of basal branches. Multiple applications of 300 to 600 ppm Configure beginning in the liner stage are recommended. Echinacea was not responsive to Augeo when applied in the liner stage but 800 ppm Augeo applied ~one week after transplanting increased branching of ‘Sombrero Hot Pink.’ Higher rates of Augeo can stunt plant growth. Echinacea is also responsive to most of the growth retardants with significant differences in rates with different cultivars.

Jim described similar studies on a variety of annuals, hanging baskets and potted crops. Augeo improved the quality of several coleus cultivars, with increased lateral branching along with a reduction in plant height. Lantana, verbena, vinca and calibrachoa were very responsive to 400 to 800 ppm Augeo applied about one week after transplanting. Again Augeo also reduced plant growth, so be cautious about using other growth retardants until you see the growth reduction effect of Augeo. Augeo also shows promise with poinsettias, replacing manually pinching with two Augeo applications early in crop production. Included was a discussion of new ideas on using Augeo for chemical pinching poinsettias.

Jim also presented an update on the use of early drenches of flurprimol or paclobutrazol to control the growth of poinsettia. These are applied to vigorous cultivars at very low rates but can be applied as needed throughout production without reducing bract size.

Joyce also used this session to launch a new iBook on “Selecting and Using Plant Growth Regulators on Floricultural Crops” written by Joyce Latimer and Brian Whipker (NC State University). Download it free of charge at www.hort.vt.edu/floriculture.
 

Latino work force

Communication and culture

By Claudio Pasian, The Ohio State University

Communication is a process by which information is exchanged between individuals through a common system of symbols, signs or behavior. When you work with Latinos, you need the right tools to ensure effective communication and work productivity. A very big barrier for a new project team where members are from different parts of the world isn’t language. It’s the “baggage” that each member carries in his/her own “cultural suitcase.” Effective communication requires an understanding of the cultural baggage and customs of your team members.

Whether you use the term Latino or Hispanic, both words designate culture, not race because Latino ancestry could be European, African, Native American, Chinese, etc. In fact, people from every continent have immigrated to the Americas. Typically, immigrant Latino workers in the U.S. horticulture industry were born and raised in rural communities in Mexico or Central America. They are young, in their 20s most likely, referring to themselves as Latinos, not Hispanics. Latinos who migrate to the U.S. for work are following a dream. Frequently, they have a basic level of education with little or no knowledge of English. Some move to the U.S. permanently, others plan to stay here for a few years for work, to send money back home, and eventually to return to their hometowns.

Cultural traits are broad, strong, pervasive and dominant generalizations about a culture such as: family, religion, education, nationalism, personal sensitivity, etiquette, personal appearance, status, aesthetics and ethics. All these influence management traits such as: work and leisure, direction and supervision, theory versus practice, control, staffing, loyalty, competition, and training as well as development, time and planning.

A few examples of work situations influenced by culture follow. Most of the advice in this brief article is for newly arrived Latino workers. Eventually, Latino workers learn the U.S. “work culture” with time.
 

Paperwork and names. In many Latino countries, a person adds his/her mother’s last name to the father’s as in “Juan Carlos Garcia Ramirez.” Juan is the first name, Carlos the middle name and Garcia is the father’s last name. Ramirez is the mother’s maiden name. So, when you file the information for this worker, under what letter will you do so? Under G or R? This may seem trivial; however, the wrong choice may result in the U.S. INS rejection of the working permit. Solution: communicate with workers about the correct way of filing their names and make notes in your records.

The work environment. Latinos are accustomed to working in groups composed of family members. While many U.S. workers thrive on competition in the workplace, Latino workers feel very uncomfortable competing against their co-workers, who often are family and friends. They are accustomed to working as a unit and valuing the results of their work as a unit. Also, self-promotion is seen as anti-social behavior.

Who will be in charge of that group? The senior family member? The person whom you select because s/he speaks some English? The person whom you put in charge of a working team may cause tension in the group if social norms are violated. Hence, job quality and productivity suffer.

The solution: in a very subtle way, ask the workers to tell you about the relationships of the workers — the hierarchy — so that you can put the right person in charge. An alternative is to let them tell you who should be in charge. Appreciation for good work usually should go to the group, not the individual.

Role of boss and employee. Latino employees expect clear, detailed instructions of what to do. In the U.S., we empower employees. For a Latino, empowerment can be misunderstood: “Isn’t that my boss’ job?” New Latino employees do not innovate on the boss’ instructions. Furthermore, they would find it inappropriate to come to you with bad news (e.g., the machine is broken).

The “No problem” problem. Also known as the “Yes problem.” Latinos desire to please others, especially the boss. Saying “No,” “I can’t do it,” or “I don’t understand,” is perceived as bad manners or controversial. The result is frustrating for U.S. co-workers and supervisors. Solution: Supervisors should explain very clearly and with specific details what needs to be done. After explaining, the supervisor should ask the worker: “Now show me how you would do it.” Stress to Latino workers that it’s perfectly OK for them to bring you “bad news.” This becomes very important because it can affect work safety.

There is no silver bullet solution that will cover all situations that an employer will face when dealing with a Latino work force. Being open minded and a constant observer of worker reactions may help in addressing the challenges that result from having a multi-cultural force.

Claudio Pasian, Ph.D., was born and raised in Argentina where he first entered the ornamental horticulture industry.

Finishing New Guinea Impatiens and SunPatiens

By Jim Faust, Clemson University

The recent concern about the future of bedding plant impatiens (Impatiens walleriana) due to downy mildew has renewed interest in New Guinea impatiens due to their resistance to this pathogen. Also, the relatively new impatiens hybrids, e.g., SunPatiens, are resistant to downy mildew and exhibit superior landscape performance to traditional New Guinea impatiens.

The genetic variation within New Guineas and SunPatiens is relatively large, so cultivar selection is key for grower success. Cultivars within any series can be selected for time to flower, since plants can be classified as early, mid and late flowering cultivars. Similarly, cultivars within any series can be classified as compact or vigorous. Therefore, varieties can be selected for uniform performance in the greenhouse, high-density production, landscape performance, etc.

For SunPatiens, Compact series varieties are easier to finish in containers and typically have greater retail appeal without the need for plant growth regulators, while Vigorous series varieties produce impressively large plants for the home or commercial landscape.

Many factors play into plant vigor besides genetics. For example, Vigorous SunPatiens are relatively compact when grow cool (<70°F), however, their true vigor is particularly noticed at warmer temperatures (>70°F). Tight spacing and water availability also impact stem elongation. Water restriction can be a more effective technique for height management of impatiens species than plant growth regulators, since over application of plant growth regulators can stunt plants for an extended period of time. Growth regulators are best used early in the crop cycle while water restriction is better for finishing, as this helps to “pop” the flowers up above the foliage, making a better retail display.

The nutrition and fertilizer needs for New Guinea and SunPatiens are similarly low. Weekly applications of 100 ppm N are usually sufficient to grow a nice and healthy crop assuming that a starter charge is in the growing media.

The temperature range at which SunPatiens can be grown expands the possibilities for finishing these plants. For example, New Guineas grow very slowly at <65°F and can be damaged by temperatures near 55°F. In contrast, SunPatiens grow very well at 65°F and can even be grown as low as 55°F. This also extends the flowering season in the fall landscape.

New Guinea impatiens have larger flowers than SunPatiens, so one open flower on a 4-inch crop or a few flowers on a hanging basket can be sufficient to generate retail sales. SunPatiens flowers are a bit smaller and often require five or more open flowers per plant to produce a high impact retail product.

Both types of impatiens are easy to propagate. SunPatiens are ready for transplant in just two weeks after stick due to aggressive rooting, and thus direct stick propagation is a viable technique for many growers. The timing of New Guineas is usually 12 to 16 weeks to market from stick, while SunPatiens can be ready in eight to 11 weeks.

While SunPatiens obviously can be grown in full sun, they have many advantages over traditional New Guinea impatiens as noted above. Perhaps the greatest is their landscape performance. SunPatiens are likely to continue to gain in popularity with landscapers gaining experience using them in both shade and sun locations. Like all impatiens, adequate water is essential for landscape success.
 

Plant Nutrition: Sherlock Holmes style

By Brian A. Krug and Claire Collie, University of New Hampshire Cooperative Extension

Understanding plant nutrition, including identifying nutrient deficiencies on the fly, can be a bit of a mystery to many growers. Identifying the nutrient deficiency is really only a fraction of the mystery; if we can’t identify why our plants have the deficiency, we are bound to experience it again and again. To unravel this mystery we need to put on our plant detective hats and go to work. And I do mean work. It is unrealistic to think that you can just look at a plant sitting on the bench and tell what is going on with it. To become the resident Sherlock Holmes in your greenhouse, you need to learn the process of diagnosing the problem.

Deficiency symptoms
Knowing nutrient deficiency symptoms is essential, yet can be one of the largest stumbling blocks. Spend some time honing your skills on identifying the symptoms

Knowing the causes of symptoms
Keep the big picture in mind because many symptoms associated with nutrient deficiencies can also be caused by a number of other factors.

Pests and diseases: To determine if the problem is caused by a biotic (pest or disease) or an abiotic (nutritional or environmental) pressure look at the pattern of the symptoms. Biotic pressures usually result in symptoms that do not follow a pattern, but have a point of origin. They spread from that point but are not necessarily symmetrical. Abiotic pressures on the other hand do typically follow patterns affecting an entire crop or section of a greenhouse evenly. Symptoms caused by the lack of nitrogen will show up evenly everywhere a particular injector is delivering (or is not delivering) fertilizer.

Water: Over-watering can predispose roots to disease and lead to root damage. When the roots become damaged they can no longer take up nutrients, even if the nutrients are present and available in the substrate. Under-watering has obvious results but can have residual effects as well. Water stress effects plant metabolism and can result in the reduction of nutrient uptake, even days after the stress event occurred.

Fertilizer: In the controlled greenhouse environment in which we work, nutrient application is required. Fertilizers can be potentially basic, potentially acidic, or neutral, therefore they can drive the pH of the substrate up or down. Fertilizer selection is crucial; selecting the wrong fertilizer for your water type (alkalinity) can cause a problem even when it is adequately delivering nutrients.

Diagnosing the problem
Once the symptoms and causes of the symptoms are understood we can get our detective’s magnifying glass (and diagnostic tools) and do some detective work. There are a few simple steps to take that, again, use the process of elimination to narrow down the cause of the nutritional disorder at hand.

Substrate testing: The first and probably most valuable tool you should use is a pH and E.C. meter, properly calibrated of course. Knowing the pH and E.C. of your substrate will begin to tell you what path to start down. Testing substrate pH and E.C. Allows you to watch trends in the substrate.

Inspect the roots: When was the last time you took a pot off of a plant and inspected the roots? Unhealthy roots cannot function properly. They may be waterlogged, diseased, or absent for one reason or another. Getting into practice of looking at roots on a regular basis can allow you to curb any problems before they get out of hand.

Fertilizer: Double check the recipe for your fertilizer and make sure that everyone in the greenhouse is mixing up stock solution using the correct recipe. Be sure to calibrate your injector. This is often overlooked but should be done regularly throughout the growing season — www.nhfloriculture.com has a short video to demonstrate how to easily calibrate your injector.

Environmental conditions: Look back at records to determine if there was a drastic change in temperature or light. As mentioned before, these parameters could be causing look-a-like symptoms.

Substrate: While you are inspecting the roots, inspect the substrate. Is it draining correctly, or is it holding too much water? Substrate physical properties can change over time, especially in long-term crops like poinsettias or hanging baskets. The breakdown of substrate physical properties can affect the health of plant roots.

Watering: Inconsistent watering can also mean inconsistent fertilization. Are all pots being consistently watered?

Tissue and Substrate Analysis: In most mystery cases, the proceeding steps will have solved the problem. However, in some cases you may opt to send out a tissue and/or substrate sample to the crime lab (aka testing laboratory) to determine exactly what nutrients are present.

Practice
Even Sherlock Holmes did not come upon his mastery of his detective skills without practice. The more time you spend keeping a close eye on your crops and using this systematic approach, the better you will become at recognizing and diagnosing nutritional disorders. With practice, the process will become easier and quicker. In short order you will be dazzling your boss by seemingly pulling the answer out of thin air, but you will know how you really worked your way through the scenario.
 

Biofungicides for soil diseases

How and why you should use them

By Pam Marrone and Chris Hayes

Overview of biopesticides
Biopesticides, regulated by the Biopesticide Pollution Prevention Division at the EPA, are naturally occurring Microbials (microorganisms used to control pests, weeds and plant diseases and Biochemicals (e.g., natural or nature-identical substances with a nontoxic mode of action, including some extracts of plants, pheromones, fatty acids). Biopesticides enjoy more than 60 years of history of safe and effective use.

The use of biopesticides is growing rapidly for pest and plant disease management in crops, turf, ornamentals, and consumer uses. While chemical pesticides are growing at 3 to 5 percent per year, biopesticides are growing at more than 15 percent per year. It is increasingly more difficult to find a new chemical pesticide that meets all of today’s requirements for efficacy along with health and safety. The cost to develop one new chemical pesticide is $250 million, so often ornamental and greenhouse uses are not top priority for registration and development.

The growth of biopesticides is driven by the benefits they bring:

• Improved pest and disease control ­— Use biopesticides alone, in rotation or tank-mixed with conventional chemistries for improved control.
• Increase yield/quality/plant health — Use biopesticides alone, in rotation or tank-mixed with conventional chemistries to get better results than chemicals alone.
• Reduce development of resistance. Most modern chemicals are single-site mode of action, so pests and pathogens can overcome them more easily than multi-site mode of action biopesticides.
• Manage residues and pre-harvest intervals — Use late season to manage residues/MRLs especially for export.
• Manage re-entry intervals — Short re-entry intervals gets workers back in quickly for pruning and other tasks.
• Low risk to beneficial organisms — No issues with water and air pollution.

Soil biofungicides
Using the right tool in the tool box can make a difference; selecting and using the proper tool can help prevent future problems. Know which biological fungicide (Biofungicide) to use and how to effectively use it will work to prevent a variety of root rotting pathogens.

Why use biofungicides? Good question. Most EPA-registered soil biofungicides are made up of two major microbial groups; fungal (Trichoderma and Gliocladium spp.) and bacterial (Bacillus and Streptomyces spp.). Since they are living, they may grow around and on the roots for weeks up to months defending the roots against a variety of root rotting fungi including Pythium, Fusarium, Phytophthora, Rhizoctonia and Thielaviopsis species. Zero to low hour REI’s allow the grower to apply in their mix line, drench tunnels or booms shortly after sticking or transplanting. Because of EPA-registration, commercial soil biofungicides have been tested not only for effectiveness but also for safety on workers, animals and the environment.

Apply soil biofungicides early to prevent root rots; if plants are sick, it may be best to apply a curative chemical before or with a biofungicide. Some biofungicides can be mixed with chemicals for an inside/outside tool of protection. Soil biofungicides can help maintain curative chemicals’ effectiveness by promoting rotation for a resistance management program. Talk about tools in the tool box.

Soil biofungicides demonstrate a variety of Modes of Action (MOA). Growing on or around roots (termed Rhizosphere Competency) allows fungal-based soil biofungicides to block fungal pathogens access to root tissue. In addition, these beneficial fungi “eat” fungal pathogens by releasing digestive enzymes that eat sugars in the cell wall of root rots (termed Mycoparasitism). Bacterial-based soil biofungicides can release cell membrane damaging metabolites that inhibit fungal pathogen growth.

Soil biofungicides are tools that work and are used by growers throughout the U.S. and Canada. Selecting the proper tool for you depends upon the root pathogen(s) you are trying to control, the environment you grow under and other inputs used in the crop cycle.
 

Understanding the nutrient management triangle - basic level

By Kimberly A. Williams, Donald Merhaut and Salvatore S. Mangiafico

Inter-relationships between root media, irrigation and fertilization are the foundation of nutrient management programs. Most growers know, as a matter of intuition and experience, that a change in one affects the performance of the others. The relationship among these components can be visualized as the Nutrient Management Triangle with fertilization, irrigation and root medium characteristics comprising the three sides, and the requirements of the particular crop in the center. If there is a change made to a component on one side of the triangle, a change in a component on another side is often necessary in order to preserve the growth, health and appearance of the crop.

To consider how to apply this conceptual water and nutrient management framework to the daily task of irrigating and fertilizing, growers should have the goal of integrating their root medium choices, fertilization program and irrigation practices into a complete, fine-tuned production system. To begin, start with consistent, repeatable, medium-handling and irrigation practices, but keep the root medium mix and fertilization program flexible enough to optimize production for individual crops or production situations.

Perhaps the most obvious relationship between the characteristics of the root medium and an appropriate irrigation program is that the water retention of a mix affects irrigation frequency. The tighter the mix, the less often irrigation is required. Another connection is that air porosity of the root medium influences percolation rate, or how quickly the irrigation solution flows through a container. This is directly related to how effectively irrigation systems like drip tubes and capillary mats will function.

Considering the effects of root medium on crop nutrition, the nutrient retention of a root medium will influence aspects of an optimum fertilization program. In general, media that have a greater ability to retain nutrients are a little more forgiving of fertilization and water quality problems. Media also house microfauna that influence, primarily, pH of the root zone.

Because irrigation water is frequently used to deliver fertilizer to crops, the irrigation schedule and fertilization program will be inherently intertwined, with irrigation frequency and amount determining optimum fertilizer application rates. The total amount of fertilizer applied to a pot through fertigation can be altered by changing irrigation volume or frequency, fertilizer concentration or the frequency of clear irrigations. In considering how root medium characteristics affect this relationship, imagine two benches of the same crop are growing side by side but in different root media, one looser. The plants in the looser mix will inevitably need to be irrigated more frequently during production. If fertilizer is applied at each irrigation at the same concentration, these plants will have more fertilizer applied to them over the course of production, though (depending on root medium physical properties) much of this “extra” fertilizer will leach out of the pot. If, on the other hand, clear irrigations are sometimes applied, these plants will be leached more over the course of production.

If the volume of leachate is large (high leaching fraction, LF), the concentration of fertilizer needs to be higher than if the volume of leachate is small (low LF) to allow the build-up of fertilizer in the root medium to optimum levels. The relationship between the amount of leaching and fertilizer concentration applied is a handy one when customizing a nutrient management system; if the LF is constant, fertilizer concentration can be easily adjusted up or down to establish varying levels of fertilizer in the root medium for different crops.

The quality of crops produced will depend largely on the root medium chosen, the fertilization and irrigation programs employed, and the interactions of these factors with environmental conditions in the production space. Understanding these components and their relationships to one another is critical to meeting production goals and addressing nutritional problems that may arise.