Hydroponics

Questions & Answers for Successful Growing

Howard M. Resh, HowardM. Resh

• Publisher: Routledge
• Year: 2017
• eBook ISBN: 9781351439510
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Biology
• Index: Biological Sciences

Drawing on the knowledge of an international leader in hydroponic food production, this book reviews many questions associated with hydroponic culture and offers useful suggestions. The questions relate to hydroponic systems, plant varieties, plant nutrition, plant culture, plant disease and pest management, environmental factors, optimum ranges, production and marketing.

Hydroponics vs. Other Cultures

1.    Many people tell me that hydroponics is any culture using an artificial medium. Is that correct?

Hydroponics is defined by word meanings as “water working,” a definition derived from the Greek words hydro=water and ponos=labor. So defined, hydroponic culture is the culture of plants, using only water as a substrate, or base, with the addition of plant essential nutrients. No substrate other than the water is used. This definition restricts true hydroponics to water culture—in systems such as nutrient film technique (NFT), the deep flow or raft culture system, aeroponic systems and possibly ebb-and-flow culture of seedlings in growing cubes.

2.    If “true hydroponics” is water culture, what are the other cultures using artificial media?

Other cultures using artificial media, as well as true hydroponics, are usually included in the term “soilless culture,” The growing of plants using substrates, or media, other than soil. Such substrates include, but are not restricted to: water (hydroponics), sand, gravel, haydite (fired clay), pumice, perlite, vermiculite, charcoal, peat, moss, bark, sawdust, wood chips, rice hulls, peanut hulls, plastic foams, styrofoam, petroleum based rigid foam-like cubes, rockwool and any mixtures containing a number of these products. Any medium that provides adequate oxygenation, water retention, good drainage, and is relatively sterile and inert is suitable for soilless culture. Note that while soilless culture includes hydroponics, hydroponic culture, by strict definition, consists of water culture without any other substrate. Both cultures use a nutrient solution to provide the plant essential elements. The choice of medium depends upon availability, cost and the plants to be grown.

Thus, in general, when we speak about hydroponics we include all forms of soilless culture. I feel that this is fine, as the cultural techniques are basically the same for all soilless cultures in that the management of the nutrient solution is key to its success.

3.    Many people argue with me that hydroponics is not organic. Do you consider hydroponics as organic or inorganic?

This is a real “red herring” question. I like to argue that greenhouse hydroponic culture is almost organic. The biggest argument between organic and non-organic centers around the use of synthetic pesticides. Pest control in greenhouse hydroponics is over 90 percent by biological agents. Pest control through integrated pest management (IPM) is the widely accepted method. This includes the use of predatory agents, which kill the pests. Some soft pesticides such as soaps (M-Pede), extracts from plants (Azatin, Neemix), bacteria (Dipel, Vectobac), fungi (Mycoprop, BotaniGard) and others are safe to use with biological agents in controlling outbreaks of infestations without damaging the predatory-prey balances. This places the hydroponic produce in “pesticide-free” status, but organic growers argue that it is still not organic due to the use of chemical fertilizers.

To be truly organic hydroponic culture should use organic sources of nutrients such as fish fertilizers, sea plant extracts, and other “natural” fertilizers, not refined ones. Many of these organic fertilizers are suitable for field crops as the soil always provides a certain level of nutrition for the plants. Hydroponic culture, on the other hand, begins without any nutrients in the substrate and generally inadequate amounts in the raw water. However, raw water often has calcium and magnesium carbonates, iron, boron, zinc and other microelements. Their levels are generally non optimum and therefore the water requires additional nutrients. Sometimes levels of micronutrients can be too high and will have to be removed from the water by reverse osmosis. Organic nutrient formulations are available for hydroponics, but often they are lacking in several elements, which will have to be added from other fertilizers, and they may be too costly for larger, commercial greenhouses. I am presently working on the development of an organic complete nutrient source from prehistoric composts that have not formed into coal. The material is steeped with water for a 24-hour period to remove the nutrients in a concentrated form. It then is prepared as a concentrated two-part liquid.

However, I suggest that inorganic fertilizers act in the same manner as organic ones in terms of plant uptake. All have to break down into ionic forms and attach to soil colloids (in the case of soil culture) and then are released into the water surrounding the plant roots (which is the same as the nutrient solution of hydroponics). Ionic exchange then takes place between the plant roots and the nutrient solution (or soil solution in soil culture). Physiologically the plant experiences no difference between the soil solution or nutrient solution ionic exchange. Therefore, I suggest that if the plants are grown pesticide free, hydroponically, it can be argued that they are really organically grown.

4.    People tell me that hydroponics is the answer to the food problems of the world. What do you think is the future of hydroponics?

Hydroponics has its niche, but I would not say it is the answer to the food problems of the world. Its primary function is in the growing of fresh, perishable crops under intensive culture. Hydroponics has become a key factor in “controlled environment agriculture” (CEA). CEA is the growing of plants for agriculture in structures—generally greenhouses—which enable us to control the environment of the enclosed crop. In addition to greenhouses, other structures such as large warehouses having artificial lighting may be used. This may be extended to highly sophisticated systems like “Controlled Ecological life Support Systems” designed for the growing of plants in zero gravity, in NASA’s space station program. Hydroponic culture is the component of these systems providing plants with water and essential elements.

Hydroponically grown products are recognized as having superior flavor and high quality, free of pesticides and disease-causing organisms. In many areas of the world such as Mexico, Central and South America, where human diseases like dysentery and cholera spread by contaminated water used in irrigating crops, hydroponic culture is becoming the method of choice for providing safe, clean vegetables. This is particularly true for fresh salad crops, including tomatoes, cucumbers, peppers, lettuce, radish, watercress, herbs and sprouts, all eaten without cooking. With consumer confidence in hydroponic products, the market for hydroponic vegetables is expanding rapidly. We will find in the near future many more commercial hydroponic greenhouse and cold frames established in developing countries as the politics and economies stabilize, creating an established middle class of people who will be looking for high-quality fresh veg etables They will be willing and able to pay a premium price for the superior quality of hydropooic vegetables, as is the case in Venezuela.

In areas like North Amenta and Europe. where a Large middle class of people demand high quality vegetables, very large greenhouse hydroponic operation are developing, especially In areas with high solar radiation and adequate water. I see a prosperous future in commercial greenhouses, concentrating on a large scale in the sunbelt areas of the southwestern Umied States and in Mexico to supply the North American demand for fresh salad crops. In Europe, such concentration of large greenhouse operations have developed in Spain (and also in Morocco) to supply the European markets.

As efficient, low-cost, artificial lighting is developed, emphasis may shift to the use of Large warehouses in or near the central core of cities, to grow low-profile crops such as strawberries, spinach. lettuce, herbs, etc. These may be tiered on shelves. Such growing of very high-density crops, efficiently utilizing the vertical space, can be automated for planting and harvesting, thus reducing production costs. Crops such as tomatoes, peppers, cucumbers, etc., which themselves grow vertically and require much higher light Intensity than the leafy crops will be more difficult and costly to grow outside the areas of naturally high solar radiation.

Of course, in space, growing crops hydroponically is the only practical method. This production, however, will serve to provide fresh vegetables to the workers of the space station itself and not be of any significance in relation to “the world food problem.” However, technology developed for the space program may have application to hydroponic growing on earth. For example, new technology in artificial lighting. water purification, disease and pest control, recirculation of nutrients and the management of long-term use of the nutrient solution will all benefit commercial hydroponics here on earth.

Site Selection

5.    People tell me that it is important to orient my greenhouse so that the crop rows will run north-south. How important is this orientation and for what crops?

Whether or not the orientation of a greenhouse is important for crop growth depends upon the crop. Low profile crops do not cast significant mutual shading among the plants. Vine crops growing vertically in the greenhouse, such as tomatoes, peppers and cucumbers, shade adjacent rows. To balance the amount of shading from one row to another the rows need to be oriented from north to south. In large operations, rows of greenhouses should be oriented in the same direction, as crop rows are normally parallel to the gutters. Of course, as you approach the equator this effect becomes less significant, as the sun is located more or less overhead. The shading effect is most pronounced during winter months in northern latitudes when the angle of incidence of the sun is very low. If rows are oriented from east to west, the most southern row of plants will receive most sunlight, with adjacent rows on the northern side receiving substantially less sunlight. This effect will be at a maximum from 10:00 AM to 3:00 PM. the period when the sunlight is of sufficient intensity to be of photosynthetic value.

6.    I have been told by other growers that greenhouses use a lot of electricity and that it is a significant cost of production. Do you have some pointers on electrical service?

The amount of amperage of electricity is a function of the size of the greenhouse operation and the number of electrical components. The more fans, pumps, lights, etc. installed the more amperage will be needed. One general rule, however, is to have three-phase power, especially for a large operation. This enables the motors of pumps, fans, etc. to be operated on 220 volts or higher, which is more efficient and less expensive.

7.    I have heard people say that if you are growing hydroponically you do not need much water. How much water do the plants use?

Availability of water is critical in greenhouse location. Even if you plan on growing low profile crops, I would suggest that you base your planning for a water supply upon the water needs of vine crops, even if you aren’t, at first, going to grow vine crops. Then you will not be short in the future should you find it necessary to change your crop according to market demand and prices, or personal interest.

A general rule for water consumption by vine crops is 1 liter (1 quart)/square foot of greenhouse area/day, during maximum usage of summer months with mature plants. Add to this volume the need for water in cooling pads, sprinklers, and water usage in the greenhouse operation itself, or packing and office facilities if those are involved.

Thinking of commercial operations, one acre of greenhouses would need at least 50,000 to 60,000 liters (about 15,000 gallons) per day. This is equivalent to a well capacity of 21 gpm (gallons per minute) over a 12-hour period. Most wells of an 8-inch casing should be able to pump 300 gpm or more as long as the drawdown on the water is met by the underlying water table. The capacity of available water can be increased by use of large storage tanks, filled from the well pump 24-hours per day. The greenhouses are then supplied with water from the storage tank by a booster pump.

8.    I have heard people say that if water can be used for drinking it can easily be used to grow plants. How important is water quality?

It is not necessarily true that drinking water can be used by plants; some drinking water may have higher than acceptable levels of micronutrients. Before formulating your nutrient solution you have to know what is in the raw water. A reputable laboratory must be called upon to test the raw water for all macro- and microelements. The elements include nitrate-nitrogen, ammonium-nitrogen, phosphorous, potassium, calcium, magnesium, sulfate-sulfur, iron, chloride, manganese, copper, boron, zinc, molybdenum, fluoride, and sodium. In addition, test for the following elements which could be toxic, or accumulate in your crop, if present in relatively high levels: chromium, lead, aluminum, cadmium, nickel, strontium, barium, vanadium, cobalt and tin. It would also be prudent to test for biological contaminants such as E. coli. If any of the microelements are in excess, it will be necessary to remove them by water treatment, such as reverse osmosis. If biological contaminant counts exceed acceptable levels, they will have to be reduced through chlorination and filtration processes.

High levels of microelements can be phytotoxic, while the presence of biological contaminants is not acceptable. Remember that hydroponically grown vegetables must be free of any disease-causing organisms. They are marketed as being high quality and clean, and therefore command a premium price.

Plant Nutrition

9. If my nutrient solution is missing an essential element can this harm the plant? What is an essential element?

An essential element is one that the plant cannot do without (it cannot complete its life cycle), no other element can substitute for it and it is an essential constituent for a plant process (metabolite). There are 16 essential elements. According to the relative quantities required they are classified as macroelements and microelements (trace or minor elements). If the plants do not have all 16 of these elements, they will not develop properly.

10. The terms major and macroelements confuse me. What are the macroelements and their sources?

There are nine macroelements: hydrogen (H), carbon (C), oxygen (0), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sulfur (S). Carbon comes from the atmosphere in the form of carbon dioxide. Hydrogen comes from the water, as does oxygen. The remaining six must be added to the water as fertilizers as part of the nutrient solution.

11. What are the microelements?

The microelements include iron (Fe), manganese (Mn), boron (B), copper (Cu), zinc (Zn), molybdenum (Mo), and chlorine (cl), Nickel (Ni) is thought to be an essential element, but as yet not proven to be one.

12. There are many scientific documents showing that other elements exist in plants. What other elements accumulate in plants and what are their functions?

A number of microelements serve a function in plants or accumulate in plant tissues, but have not met the criteria of being essential. Silicone (Si), aluminum (Al), cobalt (Co), vanadium (V), selenium (Se), platinum (Pt), lead (Pb) and others accumulate in plants. Silicone adds strength to plant cells, giving resistance to fungal infection, and is added to the nutrient solution as potassium silicate for the growing of cucumbers. Lead can be taken up, reaching levels toxic to animals or people eating the plants. Such has been the case with grasses grown in high traffic areas when cars used leaded gasoline. This was one of the reasons for eliminating lead from gasoline, to reduce its presence in the environment.

Many of these additional elements are found in raw water. They are also present as Impurities at very low levels in most fertilizers, and you add them to the nutrient solution when you use these fertilizers. If your raw water contains more than the acceptable levels of these trace elements it will be necessary to treat the water to reduce of remove them.

13. What is the source of oxygen for the plants?

Often growers overlook some of the basic functions of the nutrient solution. The nutrient solution is the principal source of oxygen to plant roots. This is termed dissolved oxygen. Oxygen is needed in metabolism, the chemical reactions of photosynthesis and respiration of plant growth and development. One of the by-products of root respiration is carbon dioxide. This may be carried in the nutrient solution in addition to other waste metabolites.

14. I understand that plants need oxygen, but what are the effects of low dissolved oxygen levels in the nutrient solution?

If the...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Dedication
• Table of Contents
• Introduction
• Hydroponics vs. Other Cultures: Questions 1 to 4
• Site Selection Questions 5 to 8
• Plant Nutrition Questions 9 to 42
• Tomatoes
• Lettuce and Herbs
• European Cucumbers
• Peppers
• Backyard Greenhouses: Questions 271 to 287
• Closing Remarks
• References
• Glossary
• Topical Index