Article 2-4 Links in the Chain
Gardening is the most popular recreational pastime in North America. It is little surprise that hydroponic gardening is gaining acceptance since a great variety of crops can be cultivated hydroponically in locations which otherwise could not be used for gardening at all. Urban residents can convert rooms, garages and patios into a family farm for food and ornamental plant production. The satisfaction derived from cultivating plants can be a deeply spiritual experience. In the truest form of "getting back to nature", a hydroponic grower is able to participate in nature by fulfilling all the needs of the crop.
In exchange, the plants help fulfill the needs of the grower by providing truly pure, fresh food; by absorbing toxic chemicals from household air and releasing oxygen; and, of course, providing visual enjoyment.
Success depends upon a variety of considerations. Just as a chain is only as strong as its weakest link, your success as a grower will be limited by the degree to which you fulfill all of the needs of your crop. Some of the links in the chain to successful cultivation include: crop selection, light, temperature, ventilation and humidity.
The type of hydroponic system and nutrient solution used are also links in the chain.
Crop selection is the primary controlling factor. Different types of plants may require significantly different environments in order to flourish. Plants have evolved in vastly differing regions throughout the world. Each region will have plant types indigenous to it which are fully adapted to the unique characteristics of that region. Tomatoes, chilies and tobacco all originated in Central America; potatoes originated in the Andes of South America; Redwood trees originated in the coastal range of Northern California. Each of these plants differ in environmental requirements.
In order to successfully cultivate a given crop is it necessary to either adapt your existing environment to meet the needs of that crop, or adapt the crop so that it will flourish in the environment which you can provide. Through selective breeding and genetic engineering we have made great leaps forward in the development of new, highly productive and disease resistant plant cultivars. These achievements constitute the foundation of modern agriculture. As a hydroponic grower, it is important to select crops which will flourish together in the same environment. Cool season crops which prefer temperatures from 60° to 65° include: strawberries, basil, lettuce, spinach, Brussels sprouts, cauliflower and peas. Warm season crops which prefer temperatures from 60° to 65° include: tomatoes, cucumbers, melons, squash, okra, eggplant and peppers. Try to choose crops that do well in the climate in which you live. Many seed companies provide plant varieties that are especially well adapted to certain areas and growing conditions. Ask a local nursery or call your local extension agent for advice.
North America is unique in that we have great climatic variations. Alaska is arctic, the Southeast and Hawaii are sub-tropical, the Southwest is arid, the Northwest is coastal-marine, and the Northeast has four distinct seasons. The result of all this great environmental diversity is that the rules which apply in one region may not apply to another. In some regions you may need to heat the growing area, in another region it may be necessary to cool the growing area. You may have to control humidity, purify the water, or make other adjustments in your area in order to meet the needs of a given crop. This is why crop selection is so important to your success.
Plants are solar collectors. They turn light into biomass through the process of photosynthesis. Many types of plants respond to changes in day length. As the daily photoperiod shortens it signals that winter is close; many plants are triggered into flowering and fruiting growth in order to produce seed for the next generation.
High intensity is a controlling factor in determining growth rate and day length is a controlling factor in determining growth phase. Long days will encourage structural growth, short days will encourage fruit production in fruiting crops. Since many urban growers must grow indoors, it is necessary to provide artificial light. The most efficient type of indoor light is called High Intensity Discharge (HID) which includes Metal Halide (MH) and High Pressure Sodium (HPS) lights. These lights will put out more light per dollar of electricity than any other type of lighting and for this reason are the only types of lighting used for commercial agriculture.
In Europe HID lights are often used in greenhouses to supplement relatively low levels of natural light, especially during the winter. The spectrum or color of artificial light is a consideration in lighting selection. Plants require primarily blue and red wave lengths, or colors. HPS are the most efficient but put out a yellowish light which is high in red light, but low in blue. MH lights provide a more natural looking "white" light and are probably the best choice if you are going to use 100 percent artificial light.
Full spectrum fluorescent lamps provide the best color balance but lack intensity and are best used for starting seedlings and cuttings. The best light by far is natural sunlight since its color balance and intensity cannot be easily matched with artificial light. However, since sunlight varies seasonally, it is likely that you will be in need of a good artificial light source to extend day length and light intensity.
MH systems are available in 100 watt through 1000 watt intensities. Generally the greater the wattage, the greater the efficiency of the light. On the other hand, it is important to know that light intensity drops off dramatically with distance. In other words, it may be best to have several lower wattage lights in various locations within the growing area instead of a single high-wattage light located in the center.
Each environment is different so this is just intended to get you thinking and not to provide all answers. Generally, inadequate light is the weakest link in the chain for most indoor growers.
Temperature, ventilation and humidity are each separate links in the chain, but they are closely interrelated. Each crop will have a range of preferred temperatures, low and high. As the temperature drops below the ideal for a given crop, growth rate will usually slow. As temperature rises above the ideal, growth rate will again slow. At extremes, the crops will die.
Plants are sensitive to temperature at both the root zone as well as above ground. Many crops will respond well to cooler nights and warmer days. Warm nutrient solution can help a crop when atmospheric temperature is on the cooler side. Warm nutrient solution will also help cuttings to develop roots more rapidly. Temperature is a controlling factor in overall growth rate.
Ventilation is also critical because plants have to breath. Leaves absorb carbon dioxide from the air and roots absorb oxygen. If a crop does not receive free flowing air, it will grow slowly. In some commercial hydroponic facilities it is not uncommon to add carbon dioxide to enrich the atmosphere. For the home hobbyist this could be hazardous if the carbon dioxide were to mix with household air.
Commercial growers using carbon dioxide enrichment must also control temperature and humidity in order to achieve a significant increase in growth rate and yield. Nonetheless, it is essential for a hobbyist to be aware of the importance of atmospheric conditions in order to cultivate a satisfactory crop.
Humidity plays a more subtle role. In order for plants to grow, they must absorb nutrients through their roots and transpire water through their foliage. In a very hot and dry environment a great deal of water can be released by the crop. In a cool, moist environment transpiration will be considerably slower. The rate at which a crop can absorb nutrients and the resulting growth rate, can be significantly affected by environmental humidity.
Plants have evolved to deal with their indigenous environmental humidity in a variety of interesting ways. The physiological character of different types of plants will often reflect the type of environment which is preferred. Plants which grow well in very humid conditions will often have lots of surface area -many broad leaves. This enables them to transpire more moisture despite the high humidity. Bananas grow in warm humid environments, lettuce grows best in cool humid environments. Both use high surface area to release moisture even in a humid environment. Plants which evolved in dry environments will have less surface area in order to slow the loss of water, a good example includes cactus, and succulents. In general, the drier the environment the more moisture the crop can transpire and the more nutrients it will be able to take in. In very humid environments many plants will grow slowly. If the environment is both cool and humid, some crops may become infested with fungus. It is important to know what temperature and humidity your chosen crop prefers.
In the final analysis this all boils down to environmental control. Success depends upon fulfilling all of the needs of the crop and doing so in a balanced way. It does little good to install a state of the art hydroponic system if you do not also provide proper lighting. The perfect hydroponics and lighting systems will not work if the conditions-temperature and humidity-are not right for the plant. Poor ventilation and very high humidity can cause crop failure even if all other conditions are perfect.
It is not necessary to become a complete fanatic and spend a fortune on equipment in order to enjoy hydroponic cultivation. However, it is essential to choose crops whose needs you can satisfy with the resources available to you.