Hydroponics

NASA researcher checking hydroponic onions with Bibb lettuce to his left and radishes to the right

Hydroponics is the growing of plants without soil. A variety of techniques exist.

Researchers of plant metabolism have discovered that plants absorb nutrients as simple ions in water. In natural conditions, soil acts as a nutrient reservoir but the soil itself is not essential to plant growth. When the nutrients in the soil dissolve in water, plant roots are able to absorb them. When the required nutrients are introduced into a plant's water supply artificially, soil is no longer required for the plant to thrive. Almost any plant will grow with hydroponics, but some will do better than others. It is also very easy to do; the activity is often undertaken by very young children with such plants as watercress.

Uses

Researcher with hydroponic strawberries

Hydroponics is useful in two main ways. First, it provides a more controlled environment for plant growth than soil thereby removing many unknowns from experiments. Second, many plant species produce more in less time and sometimes of higher quality, which under certain economic and environmental conditions, makes hydroponics growing more profitable to the farmer. With hydroponics there are no soil-borne diseases, weeds to pull, or soil to till, and plants can be placed very close to one another. This allows a large amount of food to be produced in a small amount of space. Hydroponics is also very water-efficient as it uses containers or closed loop systems that recirculate the water, and therefore requires only a small fraction of the water used in traditional farming.

These qualities combine to make hydroponics useful wherever people wish to grow plants in a non-traditional manner. Science fiction writers have long speculated that hydroponics would allow space stations or spaceships to grow their own food. The same qualities make hydroponics ideal for those who wish to grow plants with maximum control over conditions, and maximum density.

History

Some examples of earlier attempts in hydroponics are the Hanging Gardens of Babylon around 600 BC and the Floating Gardens of the Aztecs (chinampas) during the 11th century.

In 1929, Professor Gericke of the University of California, Davis demonstrated that plants could be grown soil-free all the way to maturity, growing tomato plants in water to a quite remarkable size. By analogy with the ancient Greek term for agriculture, geoponics, the science of cultivating the earth, Gericke coined the name hydroponics for the culture of plants in water (from the Greek hydros, water, and ponos, labour).

Techniques

There are a variety of techniques employed in hydroponics. Some, while dispensing with soil, use relatively inert material as a physical support for the plant roots. Other techniques dispense altogether with any growing medium, delivering nutrient solution directly to the roots by a variety of methods.

Passive hydroponics

The simplest method: the plant is planted in a container (pot or bag) of growing medium, and the container stands in a tray of nutrient solution. The medium generally has large air spaces, allowing ample oxygen to the roots, while capillary action delivers water and nutrients to the roots. A variety of materials can be used for the medium: vermiculite, perlite, clay granules, rockwool, gravel, Oasis Horticubes. Some newer media that are becoming popular are coir fibre, and cocoa bean shells. This needs the least maintenance of all hydroponic methods, requiring only topup and occasional replacement of the nutrient solution.This keeps the medium regularly flushed with nutrient and air. It is important in passive hydroponics to wash out the system from time to time to remove salt build up. This may be checked with a PPM meter, a good average reading would be about 1500 PPM. Lettuce grows well at about 800 PPM and tomatoes to 3000 PPM but both will grow reasonably well on 1500 PPM. It is important to keep the pH reading at about 6.3 to enable nutrient uptake. Data are available for the optimum settings for most plants. This is commonly employed for large display plants in public buildings: in Europe a system using small clay granules is marketed for growing houseplants.

Passive hydroponic at home - Semi-hydroponic for growing orchids

Flood and Drain (or Ebb and Flow)

In its simplest form, there is a tray above a reservoir of nutrient solution. The tray is either filled with growing medium (clay granules being the most common) and planted directly, or pots of medium stand in the tray. At regular intervals, a simple timer causes a pump to fill the upper tray with nutrient, after which the nutrient drains back down into the reservoir. This keeps the medium regularly flushed with nutrient and air.

Deep Water Culture (DWC)

Deep Water Culture is a hydroponic method of growing plants in which the roots are suspended above, and allowed to drop down into an aerated nutrient solution. This is not natural but with a properly aerated solution the roots can be continualy submerged without problems because the roots take up nutrients in the presence of oxygen. The solution is usually aerated constantly by using standard aquarium pumps and air stones, which deliver oxygen to the roots. The container holding the roots and aerated nutrient solution must be completely light proof in order to prevent algae growth. The solution must be topped up from time to time.

Drip feeding

Similar to Flood and Drain in its physical setup, except the pump delivers a continuous trickle of nutrients and water onto the medium. The emitters are commonly set to run 5 to 10 minutes every hour.

Wick feeding

A variation on Drip feeding, except that the plant draws water by means of a wick. The wick runs from the base of the plant container (e.g. a pot or a tray) down to a bottle of nutrient feed solution. The solution travels up the wick into the plant through capillary action.

Raft cultivation

A variant of DWC sometimes used for lettuces: sheets of expanded polystyrene have holes drilled through them, and young plants are placed in the holes with the roots hanging down. The sheet then floats in a shallow tank of nutrient solution.

Nutrient film technique (NFT)

In this method, the plants grow through light-proof plastic films placed over shallow, gently sloping channels. A steady flow of nutrients is maintained along the channel, and the roots grow into dense mats, with a thin film of nutrient passing over them (hence the name of the technique). A downside of the technique 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.

Aeroponics

Main article: Aeroponics

A class of hydroponics where the roots of a plant are suspended in a mist or fog of nutrient rich solution. Traditional aeroponic techniques use pumps and misters more commonly found in micro-irrigation systems, whereas state-of-the-art techniques employ ultrasonic nebulizers which render the nutrient solution into an extremely fine fog.

Media

One of the most obvious decisions a hydroponicist has to make is which medium they should use. Different media are appropriate for different growing techniques.

Expanded Clay

Also known as 'hydroton' or 'leca' (=light expanded clay aggregate), trademarked names, these small round baked spheres of clay are inert and are suitable for hydroponic systems in which all the nutrients are carefully controlled in the water. Clay pebbles can be reused provided they are cleaned thoroughly between crops. Baked clay pebbles are highly porous, yet irregularly shaped to create an balance of air space and nutrient solution.

Rockwool

Rockwool is probably the most widely used medium in Hydroponics. Made from basalt rock it is heat treated at high temperatures then spun back together like candy floss. It comes in lots of different forms including cubes, blocks, slabs and granulated or flock. When medium is dry, care needs be taken so as not inhale any particles. Inhaling such particles may carry a health risk.

Coco Coir

Coco is a compressed medium created from the husks of coconuts. Coco coir comes also in bags and in slabs. Some types of Coco coir are very high in sodium (salt) due to the nature of Coconut Palms growing on island environments and being processed in the salt air.

Perlite

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.

Vermiculite

Like perlite, 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.

Oasis Root Cubes

An open cell foam cube with a preset pH and a mild fertilizer added, Oasis root cubes produced by Smithers Oasis is the choice of large scale nutrient film growers. It is availible in many different sizes. Widely marketed in sheets sized to fit commercial trays (10"x20"), it is a convenient propogation media. Each sheet is pre-scored for easy removal of a single cube, block of cubes, or strip of cubes. Each cube has been pre-punched with a dibble hole for quick and easy seed or plant cutting insertion.

Nutrient Solutions

Plant nutrients are dissolved in the water used in hydroponics and are mostly in inorganic and ionic form. Primary among the dissolved cations (positively-charged ions) are Ca²⁺ (calcium), Mg²⁺ (magnesium), and K⁺ (potassium); the major nutrient anions in nutrient solutions are NO₃⁻ (nitrate), SO₄²⁻ (sulfate), and H₂PO₄⁻ (phosphate).

Numerous 'recipes' for hydroponic solutions are available. Many use different combinations of chemicals to reach similar total final compositions. Commonly-used chemicals for the macronutrients include potassium nitrate, calcium nitrate, potassium phosphate, and magnesium sulfate. Various micronutrients are typically added to hydroponic solutions to supply essential elements; among them are Fe (iron), Mn (manganese), Cu (copper), Zn (zinc), B (boron), Cl (chlorine), and Ni (nickel). Chelating agents are sometimes used to keep Fe soluble.

Plants will change the composition of the nutrient solutions upon contact by depleting specific nutrients more rapidly than others, removing water from the solution, and altering the pH by excretion of either acidity or alkalinity. Care is required not to allow salt concentrations to become too high, nutrients to become too depleted, or pH to wander far from the desired value.

Commercial

Due to rising awareness of chemicals and other contaminants in the food supply, people are looking for more wholesome and safer alternatives. Fortunately, hydroponics is the exact fit for the consumer’s new requirements.

Some commercial installations use no pesticides or herbicides, preferring Integrated Pest Management Techniques. There is often a price premium willingly paid by consumers for produce which is labeled "Organic". This means that lawyers and lobbyists are paid to establish rules and laws determining exactly who can charge consumers more and which produce can be legally sold with the label "Organic". Some States in the USA require soil as a "sine qua non" to obtain Organic Certification. There are also overlapping and somewhat contradictory rules established by the Federal Government. So some food grown with hydroponics can be certified organic. In fact, they are the cleanest plants possible because there is no environment variable and the dirt in the food supply is extremely limited. Hydroponics also saves an incredible amount of water; It uses as little as 1/20 the amount as a regular farm to produce the same amount of food. The water table can be impacted by the water use and run-off of chemicals from farms, but hydroponics may minimize impact as well as having the advantage that water use and water returns are easier to measure. This can save the farmer money by allowing reduced water use and the ability to measure consequences to the land around a farm.

The environment in a hydroponics greenhouse is tightly controlled for maximum efficiency and this new mindset is called Soil-less/Controlled Environment Agriculture (S/CEA). With this growers can make ultra-premium foods anywhere in the world, regardless of temperature and growing seasons. Growers monitor the temperature, humidity, and pH level constantly. In an era of farm globalization where each successive year thousands of farms are closed down worldwide due to excess capacity, only the most efficient farms will be passed down to generations in the 22nd century.

Problems with hydroponics

Although hydroponics is useful and an expanding area of agriculture, it is not without problems. One of the biggest problems with hydroponics is the need to balance the Ph of the nutrient mixtures. On large scale commercial operations computers can be used to help control the different factors, making hydroponics more complex and thus more expensive. However, the added benefit of computer controlled growing environments is that manual intervention is kept to a minimum. There are experimental computer systems which allow every aspect of the growing environment to be monitored remotely, via a network.

Luckily, hydroponics is not nearly as difficult when done on a small scale. Hydroponic systems may be as complicated or as simple as the gardener's abilities and needs dictate. Often more advanced systems will produce more abundant or higher quality crops. However even the simplest hydroponic system can yield incredible results when compared to their soil counterparts.

Present and future

With pest problems reduced, and nutrients constantly fed to the roots, productivity in hydroponics is high, plant growth being limited by the low levels of carbon dioxide in the atmosphere, or limited light. To increase yield further, some sealed greenhouses inject carbon dioxide into their environment to help growth (CO₂ enrichment), or add lights to lengthen the day, control vegetative growth etc.

Hydroponics can be used to grow plants anywhere, from Antarctica (where salad vegetables are grown in the 6 month nights) to a coal mine. If vegetables are grown in future space missions, it is likely to be by hydroponic methods.

The fact that plants can be grown almost anywhere, with no natural light by using hydroponics and lighting has not escaped the notice of clandestine marijuana growers, and a large amount of hydroponics equipment appears to be in use for this purpose. In the UK, theft of high intensity (HID) grow lamps from commercial vegetable growers is a chronic problem. However, this trend is being reduced by the increased availability, especially via the internet, of the specialist hydroponics equipment. Wide availability and low cost of equipment in the U.S. makes theft from greenhouses a rare event. In the UK, growing cannabis remains the criminal offence of trafficking. Large scale growing operations using hydroponics are often detected from abnormally high electricity consumption..