Aeroponic propagation (cloning)

Aeroponic culturing revolutionized cloning (propagation from cutting) of plants. Firstly, aeroponics allowed the whole process to be carried out in a single, automated unit.
GTi's apparatus cut-away of vegetative cutting propagated aeroponically, achieved 1983

Numerous plants which were previously considered difficult, or impossible, to propagate from cuttings could now be replicated simply from a single stem cutting. This was a major boon to green houses attempting to propagate delicate hardwoods or cacti – plants normally propagated by seed due to the likeliness of bacterial infection in cuttings.

Aeroponics has now largely surpassed hydroponics and tissue culture as means for sterile propagation of plant species. With the Genesis Machine, or other comparable aeroponics setup, any grower could clone plants. Due to the automation of most parts of the process, plants could be cloned and grown by the hundreds or even thousands. In short, cloning became easier because the aeroponic apparatus initiated faster and cleaner root development through a sterile, nutrient rich, highly oxygenated, and moist environment (Hughes, 1983).

Air-rooted transplants

Aeroponics significantly advanced tissue culture technology. It cloned plants in less time and reduced numerous labor steps associated with tissue culture techniques. Aeroponics could eliminate stage I and stage II plantings into soil (the bane of all tissue culture growers).
Cloned aeroponics transplanted directly into soil – its air roots made it all possible (1983)

Tissue culture plants must be planted in a sterile media (stage-I) and expanded out for eventual transfer into sterile soil (stage-II). After they're strong enough they are transplanted directly to field soil. Besides being labor intensive, the entire process of tissue culture is prone to disease, infection, and failure.

With the use of aeroponics growers cloned and transplanted air-rooted plants directly into field soil. Aeroponic roots were not susceptible to wilting and leaf loss, or loss due to transplant shock (something hydroponics can never overcome). Because of their healthiness, air-rooted plants were less likely to be infected with pathogens.

The efforts by GTi ushered in a new era of artificial life support for plants capable of growing naturally without the use of soil or hydroponics. GTi received a patent for an all-plastic aeroponic method and apparatus, controlled by a microprocessor in 1985.

Aeroponics became known as a time and cost saver. The economic factors of aeroponic’s contributions to agriculture were taking shape.

Deep water culture (DWC) is a hydroponic method of plant production by means of suspending the plant roots in a solution of nutrient rich, oxygenated water.

Traditional methods

Traditional methods favor the use of plastic buckets with the plant contained in a net pot suspended from the center of the lid and the roots suspended in the nutrient solution. An air pump powered aquarium air stone oxygenates the nutrient solution; if sufficiently oxygenated, the plant roots can remain submerged indefinitely. Once the plants are ready to flower, the level of the nutrient solution is gradually reduced to expose the roots to the air.

Plants absorb vastly more oxygen directly from the air than from the oxygen dissolved in water. Deep water culture allows plant roots to absorb large quanties of oxygen while also allowing the uptake of nutrients. This leads to rapid growth throughout the life of the plant.

Recirculating deep water culture

Recirculating deep water culture systems (also known as RDWC) use a reservoir to provide water for multiple buckets. Traditional methods using unconnected buckets require individual testing for pH and conductivity factor (CF). This has led to innovations that have seen the removal of air stones in favor of connecting multiple buckets together and recirculating the water. As the water is reintroduced to the bucket it is broken up and aerated with the use of spray nozzles. Constant recirculating oxygenates the water and ensures a good mix of nutrients CF and stabilizes pH throughout the entire system so testing is required only at one point.

The solution is super oxygenized from an air pump combined with porous stones. With this method the plants grow much faster because of the high amount of oxygen that the roots receive.

The DWC system requires adequate water + oxygen nourishing solution.

DWC Hydroponic System usage

It is advisable to start this type of indoor cultivation with cubes of rock wool. Once the seeds are germinated in cubes of rock wool, put them into the DWC baskets previously filled with expanded clay pellets. Fill the DWC system with water and fertilizers that are hydroponic specific up to the level of the solution in contact with the base of baskets.

In this way, the clay will be in contact with the solution that will be absorbed by the plants roots. Soon the plant will develop a large root system that will naturally immerse in the nutrient solution. It will not be necessary to maintain the level of nutrient solution to the same level of the base of the baskets, but results will come with a lower level. It is recommended replacing the nutrient solution approximately once a week and wash the container / tank with hot water to remove any algae, mould and salt deposits. Every time you fill the tank, measure the pH of the solution and ensure that its value is between 5.5 and 6.8. Revise with the pH indicator. Constantly monitor the pH.

Ebb and Flow or Flood and Drain is a form of hydroponics that is known for its simplicity, reliability of operation, and low initial investment, while providing the advantages of hydroponics.

The fundamental principle of hydroponics relies on fertilized & aerated water which provides both nutrition and oxygen to a plant's root zone, often involving relatively sophisticated mechanization which can be daunting to casual hobbyists. Nutrient solutions must usually be below the temperature at which pathogen growth can begin; yet not so cool that root activity is suppressed; active aeration of the fertilizer solution is common, since root systems themselves remove oxygen, creating conditions which also can promote pathogenic bacteria and water borne molds.

E&F utilizes the fact that the solution is not left in constant contact with the roots of plants to avoid the need for oxygenating or chilling of the solution; instead relying on characteristics of root function to provide passive oxygenation at a high level; which tends to suppress pathogen growth.

Simplicity is maintained through usage of a single, bidirectional path for the solution : water flows in, and out, the same tube: when the pump has raised water into the tray briefly submerging the roots, the pump is rendered inactive using a switch - typically a timer; and the water flows back down the same tube it was pumped up in; eliminating the need for more than one sealed fitting and reducing overall complexity of the system.

Ebb and Flood systems come on according to the water holding capacity of the medium the roots sit in; highly water retentive media can require watering only once a day; while others require twice to as many as six; with each "Flood" stage only lasting a few minutes. The time it takes to flood the roots is not a critical parameter; therefore pumps are often moderate in capacity, and can be small for systems sustaining indoor garden plants; making the method popular with amateur and urban gardeners. Gravity itself acts as drain pump; and aeration is accomplished, through thin-filming and positive displacement of air as it is forced out of the root zone by water.

Aeration of an Ebb and Flood system is an important aspect of its operation; automatic displacement eliminates air which has been de-oxygenated by the roots as the water rises to its highest flood stage; when the pump turns back off, gravity pulling the water back downward re-exposes the space around the roots to atmospheric pressure, which re-fills the voids in the medium.

The film of water left around the roots during Ebb has a high surface to mass ratio which means that even as the roots absorb oxygen, its high surface area facilitates re-oxygenation which can sustain the roots as long as their surfaces remain damp; the high oxygen content of water filmed this way suppresses most harmful life forms keeping the root zones disease free; a function that must be performed by cooling the solution in other types of hydroponics, to protect it from pythium, a form of water mold responsible for a condition called 'root rot'; wherein the outer cells of the roots die, turn brown, and slough off when handled. Need for supplementary oxygenation using air pumps is also eliminated which increases reliability; and reduces complexity.

Ebb and Flow hydroponic systems are also quiet, while using less power than other hydroponic systems which means that they can be used in environments where acoustic signature and excessive plumbing is objectionable, such as residential or classroom applications where space is at a premium.

Aeroponics is the process of growing plants in an air or mist environment without the use of soil or an aggregate medium.

Basic Principles of Aeroponics

The basic principle of aeroponic growing is to grow plants in a closed or semi-closed environment by spraying the plant's roots with a nutrient rich solution. Ideally, the environment is kept free from pests and disease so that the plants may grow healthier and quicker than plants grown in a medium. However, since most aeroponic environments are not perfectly closed off to the outside, pests and disease may still cause a threat. These conditions advance plant development, health, growth, flowering and fruiting for any given plant species and cultivars. Oxygen in the rhizosphere (root zone) is necessary for healthy plant growth. As aeroponics is conducted in air combined with micro-droplets of water, almost any plant can grow to maturity in air with a plentiful supply of oxygen, water and nutrients.

Some growers favor aeroponic systems over other methods of hydroponics because the increased aeration of nutrient solution delivers more oxygen to plant roots, stimulating growth and helping to prevent pathogen formation.

Methods

Aeroponics refers to the method of growing crops with their roots suspended in a misted nutrient solution.
Many types of plants can be grown aeroponically

Aeroponics is a form of hydroponic technique. Water is the sole nutrient carrier and typically the method is not hybridized with aeroponic technique; although due to the sensitivity of root systems aeroponics is often combined with conventional hydroponics which is used as an emergency 'crop saver' -backup nutrition and water supply- if the aeroponic apparatus fails.

In an aeroponic system the plant's root zone is suspended into an environment where the roots protrude into an atomized nutrient solution; the leaves and crown, often called the "canopy", extending above. The roots of the plant are separated by the plant support structure. The lowest stem and root system are sprayed or misted for short durations with a hydro-atomized pure water/nutrient solution.[1]

One of the more singular aspects of aeroponic growing is the frequent omission of media, whether organic or not, for anchoring the plant. Many times closed cell foam is compressed around the lower stem and inserted into an opening in the aeroponic chamber, which decreases labor and expense; for larger plants, trellising is used to suspend the weight of vegetation and fruit.

Low-pressure units

In most low-pressure aeroponic gardens, the plant roots are suspended above a reservoir of nutrient solution or inside a channel connected to a reservoir. A low-pressure pump delivers nutrient solution via sprayer nozzles or by ultrasonic transducers, which then drips or drains back into the reservoir. As plants grow to maturity in these units they tend to suffer from dry sections of the root systems, which prevent adequate nutrient uptake. These units, because of cost, lack features to purify the nutrient solution, and adequately remove incontinuities, debris, and unwanted pathogens. Such units are usually suitable for bench top growing and demonstrating the principles of aeroponics.

High-pressure devices

High-pressure aeroponic techniques, where the mist is generated by high-pressure pump(s), are typically used in the cultivation of high value crops and plant specimens that can offset the high setup costs associated with this method of horticulture.

High-pressure aeroponics systems include technologies for air and water purification, nutrient sterilization, low-mass polymers and pressurized nutrient delivery systems.

Nutrient Film Technique or NFT is a hydroponic technique whereby a very shallow stream of water containing all the dissolved nutrients required for plant growth is recirculated past the bare roots of plants in a watertight gully, also known as channels.

Ideally, the depth of the recirculating stream should be very shallow, little more than a film of water, hence the name 'nutrient film'. This ensures that the thick root mat, which develops in the bottom of the channel, has an upper surface which, although moist, is in the air. Subsequently, there is an abundant supply of oxygen to the roots of the plants. A properly designed NFT system is based on using the right channel slope, the right flow rate and the right channel length. The main advantage of the NFT system over other forms of hydroponics is that the plant roots are exposed to adequate supplies of water, oxygen and nutrients. In all other forms of production there is a conflict between the supply of these requirements, since excessive or deficient amounts of one results in an imbalance of one or both of the others. NFT, because of its design, provides a system where all three requirements for healthy plant growth can be met at the same time, providing the simple concept of NFT is always remembered and practiced. The result of these advantages is that higher yields of high quality produce are obtained over an extended period of cropping. A downside of NFT is that it has very little buffering against interruptions in the flow e.g. power outages, but overall, it is probably one of the more productive techniques.

The same design characteristics apply to all conventional NFT systems. While slopes along channels of 1:100 have been recommended, in practice it is difficult to build a base for channels that is sufficiently true to enable nutrient films to flow without ponding in locally depressed areas. Consequently, it is recommended that slopes of 1:30 to 1:40 are used. This allows for minor irregularities in the surface but, even with these slopes, ponding and water logging may occur. The slope may be provided by the floor, or benches or racks may hold the channels and provide the required slope. Both methods are used and depend on local requirements, often determined by the site and crop requirements.

As a general guide, flow rates for each gully should be 1 liter per minute. At planting, rates may be half this and the upper limit of 2L/min appears about the maximum. Flow rates beyond these extremes are often associated with nutritional problems. Depressed growth rates of many crops have been observed when channels exceed 12 meters in length. On rapidly growing crops, tests have indicated that, while oxygen levels remain adequate, nitrogen may be depleted over the length of the gully. Consequently, channel length should not exceed 10-15 meters. In situations where this is not possible, the reductions in growth can be eliminated by placing another nutrient feed half way along the gully and reducing flow rates to 1L/min through each outlet.

Top feed

In Top feed irrigation, nutrient solution is periodically applied to the medium surface. This may be done manually once per day in large containers of some media, such as sand. Usually, it is automated with a pump, timer and drip irrigation tubing to deliver nutrient solution as frequently as 5 to 10 minutes every hour.

Media

One of the most obvious decisions hydroponic farmers have to make is which medium they should use. Different media are appropriate for different growing techniques.

Expanded clay
Hydroton brand expanded clay pebbles.

Baked clay pellets, also known under the trademarks 'Hydroton' or LECA (light expanded clay aggregate), are suitable for hydroponic systems in which all nutrients are carefully controlled in water solution. The clay pellets are inert, pH neutral and do not contain any nutrient value.

The clay is formed into round pellets and fired in rotary kilns at 1200 °C. This causes the clay to expand, like popcorn, and become porous. It is light in weight, and does not compact over time. Shape of individual pellet can be irregular or uniform depending on brand and manufacturing process. The manufacturers consider expanded clay to be an ecologically sustainable and re-usable growing medium because of its ability to be cleaned and sterilized, typically by washing in solutions of white vinegar, chlorine bleach or hydrogen peroxide (H2O2), and rinsing completely.

A less popular view is that clay pebbles are best not re-used even when they are cleaned, due to root growth which may enter the medium. Breaking open a clay pebble after a crop has been grown will reveal this growth.

Rock wool (mineral wool) is probably the most widely used medium in hydroponics. Rock Wool is an inert substrate for both 'free drainage' and recirculating systems. It is produced by aerosolization of molten mineral compounds, resulting in a fibrous medium accessible to capillary action that is not degraded by microbiological activity.

Coco Peat, also known as coir or coco, is the leftover material after the fibres have been removed from the outermost shell (bolster) of the coconut. Coir is a 100% natural grow and flowering medium.

Perlite is a volcanic rock that has been superheated into very lightweight expanded glass pebbles. It is used loose or in plastic sleeves immersed in the water. It is also used in potting soil mixes to decrease soil density. Perlite has similar properties and uses to vermiculite but generally holds more air and less water. If not contained, it can float if flood and drain feeding is used. It is a fusion of granite, obsidian, pumice and basalt. This volcanic rock is naturally fused at high temperatures undergoing what is called "Fusionic Metamorphosis".

Vermiculite is another mineral that has been superheated until it has expanded into light pebbles. Vermiculite holds more water than perlite and has a natural "wicking" property that can draw water and nutrients in a passive hydroponic system. If too much water and not enough air surrounds the plants roots, it's possible to gradually lower the medium's water-retention capability by mixing in increasing quantities of perlite.

Sand is cheap and easily available. However, it is heavy, it does not always drain well, and it must be sterilized between use.

Gravel the same type that is used in aquariums, though any small gravel can be used, provided it is washed first. Indeed, plants growing in a typical traditional gravel filter bed, with water circulated using electric powerhead pumps, are in effect being grown using gravel hydroponics. Gravel is inexpensive, easy to keep clean, drains well and won't become waterlogged. However, it is also heavy, and if the system doesn't provide continuous water, the plant roots may dry out.

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