Plants & Hydroponics

What Is Hydroponics?

In its simplest definition, hydroponics is growing plants without using soil! In soil, plant roots receive all the mineral nutrients, water, gases and physical support they need from the soil but plants need to expend a lot of energy to maintain access to them.

Examples of hydroponics: (clockwise from top) rooftop vertical hydroponics, commercial- scale hydroponics, kitchen-top hydroponics

Examples of hydroponics: (clockwise from top) rooftop vertical hydroponics, commercial- scale hydroponics, kitchen-top hydroponics.

In today’s hydroponic systems, many of the biggest challenges faced by plants (such as maintaining  access to water and nutrients within a soil) are totally taken care of. Hydroponics systems deliver water containing the exact proportions of dissolved, mineral nutrients, right to the plant’s doorstep; whilst providing all the other requirements for healthy plant growth.

This means that the plants growing within a hydroponics system can divert all the extra energy that would have been used to maintain access to water and nutrients within a soil to growing more leaves, flowers and fruits- in short, the bits that we as humans like to use! The result is that the plants produce more, with fewer inputs, in less time and with less space, which are just a few of the reasons why hydroponics is being adopted around the world for commercial and home food production…

Hydroponics: A Brief History Up to the Present.

The word ‘hydroponics’ comes from the Greek ‘hydro’ (meaning water), and ‘ponos’ (meaning labour).

The historical roots of hydroponic gardening go deep into history and indeed are the stuff of legends! The mythical Gardens of Babylon, the much worshipped flooding of the Nile in Ancient Egypt, and The Floating Gardens of the Aztecs are all examples of ancient hydroponics.

The ‘modernisation’ of hydroponics began in the 1600’s with relatively simple, scientific experiments to deduce the basic requirements for plant growth. Throughout the 17- and 1800’s, more specific experiments were conducted to further our understanding nutrient, water and gas cycles within plant growth, and to discover how soil could be replaced by other materials . The biggest leaps in hydroponic knowledge were made in the 1900’s. The work of several people, Dr Gericke is notable amount them, paved the way for the first large, commercial scale hydroponic installations… In the 1940’s, the US Air Force decided that it needed a way to grow food for itself on hard-to-reach pacific islands which were rocky and had very little soil. The US Air Force decided to go for hydroponics system and managed to produce enough fruit and vegetables to sustain hundreds of their military personnel! Today, hydroponic systems are a real hit with commercial market gardeners: approximately 90% of all cut flowers purchased in the UK, and 65% of all fruit and vegetables purchased in the UK are currently grown in hydroponic systems. The development of hydroponic systems continues to this day.

What Are the Benefits and Limitations of Hydroponic Gardening?

Hydroponics can boast some big benefits over more conventional, soil-grown crops. Some of the benefits of growing plants with hydroponics are:

  • Plants can be grown in regions that were previously out of bounds due to a lack of suitable soil: this means inside big cities, dry deserts, or arctic research stations…
  • The amount of water and fertilisers required is significantly reduced. Much of the water and fertilisers applied to fields simply evaporates or flows past the plants into ground water or rivers.
  • Much less of the plants available energy is directed into growing big root systems that actively search out water and nutrients. All the water and nutrients a plant needs are right below it. This results in a more efficient use of space and significant improvements in the development of upper foliage, flowers and fruits.
  • Weeds, the arch nemesis of many traditional gardeners, are almost non-existent (and the same can be said, of most pests that can only walk or crawl): weeding time is decreased; tea-drinking time is increased.
  • Exceptional levels of gas exchange in the root zone as long as the water is fully aerated and the roots are never completely submerged. This also means that over- or under- watering is not an issue.

However, it’s not all fun and games with hydroponics! Here are some of the problems:

  • Hydroponic systems rely on the careful and continual dilution of man-made nutrients into sterile water. This process requires that the all the nutrient levels within the water are continually monitored so that none reach toxic concentrations. This process is both expensive and time-consuming.
  • The above notwithstanding, salts and chemicals inevitably build up to toxic levels, becoming wastes that need to be discharged. This creates the inconvenient and problematic issue of where to dispose of all that toxic water…

But, I hasten to add, the problems outlined above are all virtually none-existent in aquaponics due to the fact that aquaponic systems rely on a biological community to turn many of the problems inherent in hydroponics (otherwise known as wastes) into resources; this arrangement is opposed to hydroponics in that wastes are seen as just that, and thus are a problem! Consequently, aquaponic systems commonly outperform hydroponic systems: for further information on aquaponics outperforming hydroponics , see this article from the Aquaponics Journal: http://www.aquaponicsjournal.com/docs/articles/Greenhouse-Aquaponics-Proves-Superior.pdf . More information on aquaponics is available throughout the site, but for now, back to hydroponics!

 

What Are The Most Common Types of Hydroponic System?

Nutrient Film Technique (NFT) Systems:
NFT was the original hydroponics technique and it remains popular today due to its simplicity and cheapness.

The premise is that the plants are held above a table that is slightly slanted to one side. Water is pumped from a reservoir to the top of the table and allowed to flow down over the surface of the table in a thin film, 1-3mm deep. When the water reaches the bottom of the table, it is directed back into the reservoir to complete and completes the cycle. Nutrients and air are added into the reservoir.

The main disadvantages of this technique are that: the roots are constantly submerged in water, increasing likelihood of bacterial disease and reducing aeration of the root ball; their small pumps are prone to breaking; and because the roots don’t have much to cling to, big plants have a hard time standing up! However, despite the above, these systems are very productive, and as mentioned before, both simple and inexpensive. NFT systems are sometimes modified to support aquaponics.

Drip Irrigation Systems:
Drip irrigation systems grow plants in a rockwool slab. The plants are individually fed using drippers, which in turn are fed from a central reservoir. Commercial systems are usually fed under high pressure and only allow the water to circulate the system once; after that, the nutrients are bled-off and the water directed into a drain for disposal. Such systems dominate the Dutch horticultural industry. Domestic systems on the other hand are largely the same but are low pressure, and usually recycle their water.

On the plus side: drip irrigation systems are very versatile; productive; and cheap to build. On the negative side: running costs are high- the rockwool is replaced with every crop; nutrient losses are high if you run a system that goes straight into a drain after one drip through the rockwool; and high levels of maintenance are required on both high and low pressure systems. Not recommended for a beginner!


Deep Water Culture (DWC) Systems:
DWC systems are the simplest of hydroponic systems and evolved for domestic use. They are cheap, work well, but do require a fair amount of maintenance.

Essentially DWC hydroponic systems are all contained within one container with a lid. A hole is cut in the lid through which a plant is suspended by a plastic basket filled with clay balls. An air stone is placed in the bottom of the container which serves to: mix the nutrients with the water; cause spray to hit the clay balls above creating a moist growing environment; and of course, to aerate the water with oxygen. Once the roots of the plant have grown down below their basket, they will be continually submerged in water. Essentially, DWC systems grow plants in their own water reservoir.

On the plus side, DWC systems are extremely cheap to make due to their simplicity. However, there are two main disadvantages to DWC systems. Firstly, the roots of a mature plant are continually submerged and thus, are very vulnerable to water-logging and oxygen starvation if  the pump stops working or becomes clogged. Secondly, the containers for DWC hydroponic systems are generally not very big and cannot hold large volumes of water (maybe5- 10 litres). This means that the nutrient concentrations and pH level within the system can fluctuate very quickly, as can the water level depending. The result is that the system needs to be checked very regularly to prevent your plant from suffering. Unless you only fancy growing one or two plants, DWC systems are not recommended.

Flood and Drain (also known as Ebb and Flow) Systems:
A Flood and Drain does exactly what it says on the tin- it floods a grow bed (filled with a permeable media), and then drains it. The advantages of this system are that as the bed is filled with water old air is pushed out of the air pockets between the media; and as the water drains out, new air is pulled in- this means that aeration of the rootball, which sits in the media, is excellent, whilst access to water and nutrients remains high!

The grow beds are fed using a pump submerged in a large reservoir, located beneath the grow beds. The flood and drain pattern can be achieved in one of two ways. Either the pump is on a timer, meaning that it will pump water into the grow bed until it is full, after which time the water drains back into the reservoir under gravity. Or, the pump is on constantly and an automatic bell siphon causes the water level within the grow bed to continual fill and drain. Pumps that are continually turned on and off break more often than those that are continually on. Therefore, the latter method will probably be cheaper!

The flood and drain system is a real winner. It is very simple and effective! The only negative I can think of is that if you use clay balls as your media, they need to be washed before they are used to prevent clay dust engulfing every part of your system.
(This is the system most popular with home aquaponic gardeners!)

Aeroponics:
The theory of aeroponics is that the roots of a plant are suspended in the bare minimum of media and are continually sprayed with a fine mist of nutrient rich vapour. The misting action means that aeration of the water is second to none. This is all very well but the nutrients dissolved in the water tend to precipitate (separate from the water and solidify) around the mouth of the misters very quickly, rendering them useless- sometimes in a matter of hours! More modern aeroponics systems, to some degree, solve this problem by using a spinning, high-frequency sprayer which sprays the root ball from below. However, the high- pressure systems tend to blast fine roots into a tangled soggy clump whilst low pressure systems don’t generally deliver enough water and nutrients. The equipment is also fairly expensive. Although, despite these drawbacks, aeroponics systems can still deliver good results.

See more about planting in aquaponics here…

What Factors In A Hydroponic System Require Management?

The primary difference between hydroponic gardening and gardening in soil is just that; there is no soil. However, the majority of principles that apply to growing plants in soil-base systems also apply to growing plants in hydroponic systems. Therefore, it is the job of the hydroponic gardener to uphold and apply the normal principles of growing plants in soil, when growing  plants without soil! This requires that many environmental factors, such as the concentration of nutrients and oxygen within the water, are artificially controlled and managed. The factors listed below all require management:

  • Nutrients:
    Nutrients are absolutely critical to raising healthy plants that reach their full potential. In hydroponic systems, plant nutrients are dissolved within the water- each nutrient at a different concentration according to their importance for plant growth. It is the job of the gardener to monitor and maintain these concentrations so that they remain at an optimum level for plant growth. Nutrient levels are measured indirectly using a digital EC (electric conductivity) meter. Nutrient concentrations are maintained within the water by the regularly dissolving a ‘nutrient solution’ directly into the circulating water (bottles nutrient solution can be purchased from any hydroponics equipment supplier).Nutrients can be divided into two groups: macronutrients; and micronutrients, also known as trace elements. Macronutrients are need in relatively high quantities; micronutrients, are needed in ‘trace’ amounts. It’s worth getting to know all of them and why they are important, and essential to know how to administer and monitor them. Below is a list of all the know nutrients know to be essential for plant growth, (describing the ins and outs of all them is beyond the scope of this article though, so we recommend getting a good book on the topic!):The macronutrients: Nitrogen (N);  Phosphorous (P);  Potassium (K); Calcium (Ca); Magnesium (Mg); and Sulphur (S).
    The micronutrients: Iron (Fe); Boron (B); Manganese (Mn); Zinc (Zn); Copper (Cu); Molybdenum (Mo); and Aluminium (Al).
  • Water Aeration:
    The purpose of aeration is to dissolve as much oxygen into your water as possible! Plants absorb around 1% of their total oxygen requirement through their roots. In addition, a large dissolved oxygen concentration (DO) helps to keep the water free of pathogens and the roots to absorb nutrients.
    Good dissolved oxygen concentrations are achieved by placing aerators directly into the water (these blow bubbles into the water) and by breaking the surface of your water (as when water splashes from a tap into more water). Leaving the roots of your plants to dry out occasionally is a good idea too!
  • Water pH:
    The pH value of a water body is a measure of how acidic or basic it is. pH is measured on a logarithmic scale of 0- 14: 0 being the most acidic; 14 the least. Water pH is important in hydroponics because it affects the solubility of nutrients within water, and thus influences how accessible they are to plants. As can be seen from the graph below, the majority of nutrients that plants require are soluble, and thus available to them, within a range of  pH 6 to 7 (width of bar indicates availability). It is worth noting that if  your growing medium is particularly alkaline, you should keep your water pH at a slightly lower level than normal to compensate. The pH of your water can be measured using either: paper test strips; liquid pH test kits; or digital pH meters.

 

  • Temperature:
    Like all living things, temperature is crucial to healthy growth. Some plants like it cool; and some like it hot…:  knowing what temperature is best for the particular plants in your system (in both the air and in the water) is crucial to promoting healthy growth.
  • Ventilation:
    Plants require carbon (C), oxygen (O), and hydrogen (H) to grow. They obtain the vast majority of these elements from gases in the atmosphere, so keeping your grow-room ventilated is very important. If you are growing in a closed environment, this will usually mean installing an extractor fan in the top of the room to pull stale air out; and a corresponding hole in the bottom of the room to allow fresh air in. If you are growing in a green house, leave some windows open.
  • Light:
    Plants require light to photosynthesize- the more they have, the faster they can produce the food they need to grow and thrive. Lighting requires either that you use natural sun light, or that you buy specialised growing bulbs which emit the full spectrum of light that plants require. Care should be taken not to ‘burn’ plants by exposing them too much to the sun or to artificial lighting- the level of light required to burn a plant depends on the species.
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