Cloning 101

Cloning allows you to grow an exact copy of your plant by using the original plant roots. Here is a basic guide to cloning your plants.

What You'll Need...

Tray & Dome                             Light                         Growing Medium      
          1. On your plant look for a spot where there are branches growing out and a new top, and cut a little bit below that. Cut the branch away at a 45 degree angle. You want probably around 5-8 inches to cut for your new clone. 
          2. Now choose the growing medium you are going to use. There are Jiffy pellets, Rockwool, Rapid Rotter cubes, or loose soilless mix. Pre-soak which growing medium you prefer. Also choose which rooting hormone you prefer- powder or a gel. Give a light coating of either on the stem of your cut and insert it into the medium. 
      1. Arrange your "planted" cuttings in your tray and your dome. The dome will provide humidity and keep heat in. Under the tray it is preferable to put a heating mat. This will increase your chances of rooting. Make sure there is no water in the bottom of the tray.  
      2. On top of your dome you will want to put a propagation light. We recommend the T5HO Sunblaster 6400k light or even better, the 18" Clone LED from Quick Grow Supercenter.                                                                                                                                                                                                                                                                                                                                                                                                                                  
      3. Do Not Spray your cuttings. We are trying to get the clones to want to look for water, in order to do that they must grow roots to find it. If the humidity in the dome is too high they will have sufficient moisture to be able to survive without growing roots. After 5-7 days you will need to water the cuttings. You can remove each one and dunk them in water or you can water in tray, but remember to drain the excess water.                                                             
      4. Within 14 days you should have signs of new roots that signify you can transplant to a new container.


Plant Hormones and Thiamine (Vitamin B1)

Hormones are produced naturally by plants, while plant growth regulators are substances applied to plants to influence growth and development in some way. All plant hormones and plant growth regulators (PGR) are in fact ‘organic’ in that they contain carbon and nitrogen however these can be divided into either synthetic (man made) compounds (such as IBA used in rooting powders/gels, or cycocel) that mimic naturally occurring plant hormones, or they can be naturally occurring substances that have been extracted from plant tissue (e.g the cytokinin ‘zeatin’ is extracted from maize). Whether a plant growth regulator is naturally derived and extracted from plant tissue or synthetic can have a major effect in terms of the result on plant growth. Naturally derived PGRs, can be absorbed and deactivated inside plant tissues where as synthetic PGRs due to their chemical structure are resistant to break down inside the plant.

Plant growth regulator substances are usually applied in low concentrations to plants as only a few parts per million is sufficient to have the required affect. Most often these types of compounds are applied as a foliar spray, although some work best if applied as a seed soak, or media drench around the plants base. The method of application of various PGRs depends on what compound is being used for a particular purpose, but usually their effects are short lived, and repeated applications are required to achieve the desired result.

There are 4 groups of PGR compounds: these are Auxin, Gibberellins (GA), Cytokinin and Ethylene. While auxins, gibberellins and cytokinins are considered to be growth promoters. Ethylene is a gas which can cause leaf abscission and ripening of certain types of fruit, however when applied at the correct concentration as Ethrel (foliar spray) it has been used to induce femaleness in flowers of cucumber and other dioecious plants.

Auxins are most widely used to stimulate root formation on cuttings and are often used in the form of NAA or IBA, although they have other horticultural applications as well such as promoting fruit set in some plants such as tomatoes.

Gibberellic acid (GA) can have the effect of increasing plant height by elongation of the internodes on plants. GA also increasing the rate of germination and break bud dormancy. GA stimulates cell division and elongation, and will stimulate bolting or flowering in some plants by causing cells in the flower bud to divide and expand lengthwise more rapidly than normal. Synthetic compounds such as Cycocel have been produced which are ‘anti-gibberellins’ and force a plant to remain dwarfed by blocking the elongation effect of the plant’s natural Gibberellins.

Cytokinins (such as BA or BAP, or Kinetin, Zeatin): Cytokinins promote cell division, they also promote the growth of lateral buds and stimulate leaf expansion resulting from cell enlargement. Cytokinins also slow down ageing or senescence in leaves, allowing them to stay green and actively photosynthesising for longer.

When using PGRs the timing of application is important. Many PGRs only work when applied at a certain stage, and some are more effective if applied in the root zone where up take can be much greater than when spayed on the foliage.

Many of the other naturally derived PGRs are best applied to the plant part which they are to effect (i.e sprayed on the flower buds, foliage, or applied to where roots are to form).

Thiamine (Vitamin B1):

B1 is produced in the foliage of plants and transported down to the root system where it has an effect on root growth and development. In tissue culture and rooting preparations, B1 helps to stimulate the growth of roots on new plants but this is best used in combination with rooting hormones. B1 can assist at any time in a plant’s life with root regeneration where the root system has been damaged or stressed through high salinity, pathogens such as pythium, nutrient deficiencies and toxicities, high fruit loading etc but only if the foliage of the plant is unable to produce sufficient supplies for this purpose. Use of B1 is seen as a ‘back up’ or ‘insurance policy’ as it is difficult to determine if a plant which has come under stress is capable of producing sufficient B1 to send down to the root system to assist in cell development. Use of Vitamin B1 in plants is the same as in humans – it is most useful where a deficiency exists for some reason. B1 is best applied as a seed soak to speed up germination (root growth), or as a foliar spray.

B1 is an organic compound and as such is rapidly broken down by microbes in the nutrient solution (they love to eat carbon based compounds), adding high amounts of B1 may ensure sufficient thiamine stays in the nutrient for a few hours for some plant uptake, but generally microbes will break this down rapidly as well.

Hydrogen Peroxide and Horticulture

Hydrogen Peroxide and Horticulture

By Bryce Fredrickson

Hydrogen Peroxide (H2O2) is a clear sharp smelling substance very similar in appearance to water (H2O). Like water it is made up of Hydrogen and Oxygen, however H2O2 has an extra Oxygen atom in an unstable arrangement. It is this extra atom that gives H2O2 its useful properties. H2O2 has been used for many purposes including cleaning, bleaching, sterilizing, rocket fuel, animal feed treatment and in addition many miraculous claims about its health benefits have been made. This article isn’t about any of these; instead it will concentrate on horticultural applications. H2O2 is of great use for both hydroponics and dirt/soilless gardening.

1. What Does Hydrogen Peroxide do?

H2O2 is an unstable molecule, when it breaks down a single oxygen atom and a molecule of water is released. This oxygen atom is extremely reactive and will attach itself to either another O- atom forming a stable Oxygen molecule or attack a nearby organic molecule. Both the stable and O- forms will increase the level of dissolved oxygen. This is the method by which H2O2 is beneficial. Pretreating the water supply with H2O2 will drive out the Chlorine many cities use to sterilize it. This will also degrade any pesticides or herbicides that might be present as well as any other organic matter. Well water can be high in methane and organic sulfates, both of which H2O2 will remove. Many disease causing organisms and spores are killed by Oxygen, the free Oxygen H2O2 releases is extremely effective at this. H2O2 will help eliminate existing infections and will help prevent future ones. It is also useful for suppressing algae growth. The free Oxygen atom will destroy dead organic material (i.e, leaves roots) in the system preventing them from rotting and spreading diseases.

2.Over Watering 

Roots require Oxygen to breathe and low levels are the main cause of almost all root diseases. Both soil and hydroponic plants often fall prey to the same syndrome although it is rarely recognized as what it really is. Hydroponic crops often fail due to “root rot” and soil crops succumb to “over watering.” The real cause of both these problems is a shortage of Oxygen at the root zone. In a soil system the soil consists of particles, a film of water on the particles and air spaces between the particles. When too much water is put into the soil the air spaces fill with liquid. The roots will quickly use up what Oxygen is dissolved in the water, if they haven’t drunk enough of the liquid to allow air back in to the soil spaces they will stop working. In this situation roots will start dying within twenty-four hours. As the roots die the plants ability to drink water and nutrients will decrease, this will cause symptoms of nutrient deficiencies (mostly pale, slow, weak growth), and strangely they will start to wilt like they don’t have enough water. It is easy to make a fatal mistake at this point and add more water.

In a Hydroponic system the cause is a more direct simple lack of oxygen in the solution, this may be from inadequate circulation and/or aeration. High reservoir temperatures also interfere with Oxygen’s ability to dissolve in the water. Temperatures above 70F (20C) will eventually cause problems, 62F-65F (16C-18C) is recommended. The same symptoms will appear as with soil plants but you can also check the roots. Healthy roots should be mostly white with maybe a slight yellowish tan tinge. If they are a brownish colour with dead tips or they easily pull away there is at least the beginnings of a serious problem. An organic dirtlike rotting smell means there is already a very good chance it is too late. As roots die and rot they eat Oxygen out of the water, as Oxygen levels are even further depleted more roots die, a viscius circle may be well under way. Reduced Oxygen levels and high temperatures both encourage anaerobic bacteria and fungi. The plants may still be saved but you will have to work fast.

3. How Hydrogen Peroxide prevents root rot/overwatering. 

When plants are watered with H2O2 it will break down and release Oxygen into the area around the roots. This helps stop the Oxygen from being depleted in the water filled air spaces until air can get back into them. High Oxygen levels at the roots will encourage rapid healthy root growth. In a Hydroponic system H2O2 will disperse through out the system and raise Oxygen levels as it breaks down. Strong white healthy roots with lots of fuzzy new growth will be visible. This fuzzy growth has massive surface area allowing for rapid absorption of the huge amounts of water and nutrients needed for rapid top growth. A healthy plant starts with a healthy root system.

4. How to use it. 

H2O2 comes in several different strengths 3%, 5%, 8% and 35%, also sold as food grade Hydrogen Peroxide. The most economical is 35% which we recommend be diluted to three percent before using, as at this high concentration it can cause damage to skin and clothing. When working with food grade H2O2 it is very important that you clean up any spills or splashes immediately, it will damage almost anything very quickly. This is extra important with skin and clothing. Skin will be temporarily bleached pure white if not washed cleaned. Gloves are strongly recommended when working with any strong chemical.

Food grade H2O2 can be diluted to three percent by mixing it one part to eleven parts water (preferably distilled). The storage container should be opaque to prevent light from getting in and it must be able to hold some pressure. If three-liter pop bottles are available in your area they are ideal for mixing and storing H2O2. There are twelve quarter liters (250ml) in three liters, if you put in one quarter liter H2O2 and eleven quarter liters (250ml) water in the bottle it will full of three percent H2O2 and the bottle can hold the pressure that the H2O2 will generate. Three percent Hydrogen Peroxide may be added at up to three ml’s per liter (2 1\2 tsp. Per gallon), but it is recommended that you start at a lower concentration and increase to full strength over a few weeks. Use every watering even on fresh cuttings. For hydroponics use every reservoir change and replace twenty-five percent (one quarter) every day. Example: In a 100L reservoir you would add three hundred ml’s (3%) H2O2 when changing the nutrient. You would then add seventy-five ml’s more every day.

5. Where to get it. 

35% food grade: called food grade because it has no toxic impurities
Of course your local hydroponics retailer, whom you can locate over the web at Direct order off the web (there may be shipping restrictions on high strength peroxides). H2O2 is used to bleach hair so the local hairdresser may have a source. The local feed supplier may have it in small towns. Prices range from fifteen dollars per quarter liter to eighty dollars a gallon. One gallon will treat up to fifty thousand liters of water.

3%5%, 8%
Can be found at most drugstores or pharmacies, prices start at a less than a dollar for a one hundred-ml bottle that will treat one hundred liters.

6. What to do if you already have root rot.

In Dirt:
Use peroxided water with anti-fungicide (benomyl) and a high Phosphate fertilizer (9-45-15, 10-52-10, 0-60-0) for root growth. Root booster (5-15-5) or any other product with rooting hormone dissolved in it is helpful in regrowing roots and is strongly recommended. If a plant is wilty adding Nutri-Boost may save it. Water heavily until liquid pours out the bottom of the pot. This sound like bad idea, but it flushes out stagnant dead water and replaces it with fresh highly oxygenated water. Don’t let plants sit in trays full of water, the soil will absorb this water and stay too wet. Don’t water again until the pot feels light and the top inch or two of the soil are dry.

In Hydro:
Change your nutrients. Add H2O2 to the system. This will add oxygen and chemically eat dead roots. If roots are badly rotted and can be pulled away by hand you should pull them off. They are already dead and will only rot, causing further problems. Add a fungicide to kill any fungus that is probably present in the rotted tissue to prevent it from spreading. Root booster will speed recovery. If plants are wilty Nutri-Boost may help save them. Increase aeration of the water, get an airpump and air stones, or more of them, for the reservoir. An air stone under every plant is usually very effective, but will require a larger air pump. Models that will do from forty to four hundred stones are available. Decrease the reservoir temperature, oxygen dissolves better in cold water and disease causing organisms reproduce slower as well. A good temperate range is 62F to 65F; anything above 70F will eventually cause a problem. It is also a good idea to remove any wilty plants from the system and put them on a separate reservoir so they don’t infect plants that are still healthy.


The key to big productive plants is a big healthy root system and Hydrogen Peroxide is a great way to keep your roots healthy. It is a must to ensure the biggest best crops possible and to increase the chances of your plants thriving to harvest. Peroxide users will rarely lose plants or crops to root disease and will harvest larger and more consistent crops. 

Dissolved Oxygen Levels and Nutrient Temperature- Battle the Pythium Virus in Hydroponics

The essential for consistence in harvests with the utmost quality and yield.

The hydroponic nutrient solution is not just a mix of fertilizer salts and water, there are a number of organisms and compounds commonly found in our hydroponic systems that we need to be aware of. One of the most important of these is dissolved oxygen which is vital for the health and strength of the root system as well as being necessary for nutrient uptake.

Most growers are familiar with the need to have some form of aeration in their nutrient solution – whether they be in a recirculating or a media based system. In NFT systems, this is often accomplished with the use of an air pump or by allowing the nutrient to fall back into the reservoir thus introducing oxygen. However, the effect of temperature of the solution on the dissolved oxygen levels and on root respiration rates also needs to be taken into account. As the temperature of your nutrient solution increases, the ability of that solution to ‘hold’ dissolved oxygen decreases. For example, the oxygen content of a fully aerated solution at 10C (50 F) is about 13ppm, but as the solution warms up to 20 C (68 F) the ability of the liquid to ‘hold’ oxygen drops to 9 – 10ppm, by the time the solution has reached 30 C (86 F), then it’s only 7ppm.

While this may not seem like a huge drop in the amount of dissolved oxygen, we have to remember that as the temperature of the root system warms, the rate of respiration of the root tissue also increases and more oxygen is required by the plant. For example, the respiration rate of the roots will double for each 10C rise in temperature up to 30C (86 F). So the situation can develop where the solution temperature increases from 20 – 30C (68 – 86 F) during the day, with a mature crop, then the requirement for oxygen will double while the oxygen carrying capacity of the solution will drop by over 25%. This means that the dissolved oxygen in solution will be much more rapidly depleted and the plants can suffer from oxygen starvation for a period of time.

The symptoms of oxygen starvation which can occur in both NFT and media based systems can be difficult to pick up as they are very general signs. Media based plants are just as prone to oxygen starvation in hydroponic systems as those grown in solution culture, but here we must also take into account the ‘air filled porosity’ of the media used. This is simply how much air can permeate between the particles in the substrate and selection of a free draining media which won’t break down will ensure that maximum aeration is going to reach the root zone. Injury from low (or no) oxygen in the root zone can take several forms and these will differ in severity between species. Often the first sign of inadequate oxygen supply to the roots is wilting of the plant during the warmest part of the day when temperature and light levels are highest. Insufficient oxygen reduces the permeability of roots to water and there will be the accumulation of toxins, thus both water and minerals cannot be absorbed in sufficient quantities to support plant growth particularly under stress conditions. This wilting is accompanied by slower rates of photosynthesis and carbohydrate transfer, so that over time, plant growth is reduced and yields will be affected. If oxygen starvation continues, mineral deficiencies will begin to show, roots will die back and plants will become stunted. Under continuing anaerobic conditions, plants produce a stress hormone – ethylene which accumulates in the roots and causes collapse of the root cells. Once root deterioration caused by anaerobic conditions has begun, opportunist pathogens such as Pythium can easily take hold and rapidly destroy the plant.

Another more visible and longer term effect of oxygen starvation which also occurs in waterlogged crops is leaf ‘epinasty’. Epinasty is a downward curvature of the plant leaves, resulting in plants which look wilted. If the oxygen starvation continues and is severe, then eventually leaf chlorosis yellowing, premature leaf and flower abscission will occur.

There are a number of things we can do to make sure our nutrient solution is carrying sufficient dissolved oxygen, and this is important when we consider that many of the root diseases encountered in hydroponics have occurred because the root system was damaged in some way, with anaerobic conditions being a major factor in many situations. The first most important factor to remember with oxygen is that the best way to introduce this gas into the nutrient is to have the solution fall back into the reservoir, and the greater the drop height, the better the aeration effect. Breaking the flow up into a fine shower also assists by introducing more air bubbles into the tank. Secondly, while nutrient ppm (EC) does reduce the oxygen carrying capacity of the solution, the effect is very small and temperature has a much greater influence on oxygenation. Reducing excessive solution temperatures will ensure more oxygen can be held by the solution and the rate of respiration by the roots will be kept down to optimal levels. Thirdly factors such as nutrient flow rate, channel width, length and slope have a large effect on oxygen levels- faster flow rates, greater slopes and shorter channel lengths all assist with prevention of oxygen starvation.

Perhaps one of the commonest problems in hydroponic systems is the Pythium pathogen and what many growers don’t realize is that Pythium being an ‘opportunist’ fungi, often takes advantage of plants which have been stressed by a combination of high temperatures and oxygen starvation in the root zone. Pythium is usually described as a ‘secondary infection’ meaning that the Pythium spores which are actually common in just about all hydroponic systems, don’t actually attack the plant until it has been damaged in some way. Even very clean hydroponic systems and grow rooms which are isolated from the outdoor environment will have some Pythium present as these fungal spores are naturally present everywhere on a world wide scale – in the water, soil, vegetation, carried in the air and in dust, so its difficult to eliminate the source of this disease. However, one way we can reduce the ‘spore load’ is to sterilize any water supply which may be contaminated with high levels of pythium – water from dams, and streams should always be sterilized before use for this reason if Pythium is a problem.

Under the right environmental conditions, virtually every plant species is vulnerable to Pythium, which not only causes ‘damping off’ of seedlings but causes root and stem rot of older plants. Symptoms of Pythium on older plants are a wet rot, root systems will be browned, roots hollow and collapsed. Plants may appear to grow poorly, and wilt for no apparent reason – indicating that an examination of the root system is called for. Pythium has an optimum temperature range for infection of plants, this is generally between 20 – 30C (68 – 86 F), although infection can occur outside this range when damaged plant tissue is available for rapid colonization by the pathogen. Low concentrations of Pythium that may not cause problems at lower temperatures will be disastrous at higher temperatures, particularly where the warmer conditions are associated with a lack of oxygen in the root zone and plant stress.

The best preventative measure against Pythium attack is a healthy, rapidly growing plant as this is an opportunist pathogen and will enter at the site of tissue injury or if the plants are overly succulent, weakened or stressed for some reason. Often root damage during the seedling stage as plants are introduced to the hydroponic system is a danger time for Pythium infection. Pythium is of greatest threat during the seed germination and seedling development stage when plants are most vulnerable to attack, and adequate control and elimination of the pathogen during this stage is the best preventative measure of Pythium control in hydroponic systems. Strong healthy plants will develop resistance to Pythium attack during the seedling stage and this will prevent problems at a later stage of growth.

Other preventative measures include the use of a well drained media, thorough disinfecting of all equipment between crops, and control of pathogens during the seedling stages with a suitable fungicide, long before they are introducing into your hydroponic system. Occasionally a very high spore load, combined with excessive temperature will result in Pythium attacking even healthy plants, if this is the case, it is likely that there is an active source of spore production present, and the system must be shut down and disinfected. Sterilization of the water supply with UV light, hydrogen peroxide or ozone , before nutrient are added however, is effective at reducing or eliminating Pythium from the original water supply.

Therefore by ensuring your plants are healthy and stress free, you will not only get the highest growth rates possible, but also prevent problems such as Pythium infection occurring. The variables to remember with regard to the nutrient solution is that aeration is vital to maintain the dissolved oxygen levels, temperatures should be keep within an optimum range, and Pythium is always present, but a healthy plant is the best measure of protection against a disease outbreak. About the oxygen requirement of plants when in flower…its not always the case that plants require more oxygen because they are in flower, a plants oxygen requirement is linked to the size of the root system, temperature and nutrient uptake rates, rather than the presence of flowering. So since plants such as tomatoes tend to have a rapidly developing root system at the time of flowering, its important to maintain adequate oxygen levels. With tomatoes the requirement of oxygen in the root zone increases gradually up until the time of maximum fruit load and rapid fruit expansion, where the high rates of nutrient uptake increase the oxygen requirement quite dramatically. On the other hand, if oxygen is deficient during flowering, then the flowers and subsequent fruit may drop off as a result, or they may be undersized. 


Aeroponics – Misting Frequency and The Root Systems

Aeroponic systems, which use a mist of nutrients over the plant roots, inside a growing chamber. Producing faster growth rates, high yields and healthy roots. As long as the plant rooting chamber is being kept between 62F – 71F consistently. Some of the more sophisticated commercial greenhouse systems are temperature linked. The temperature is continually monitored in the root chambers, when pre-set temperature is triggered the mister system is activated to bring temperatures down.

Simple Misting Time

One method of delivering nutrient spray in commercial aeroponic systems is the ‘regular, intermittent misting cycle’. This is a burst of nutrient solution, misting 3 minutes every 5 minutes. By using this technique, which does not change during the life of the crop, the misting cycle never causes the plant’s roots to dry out. The emphasis here, is on regularly delivery fresh aerated, temperature adjusted nutrient to the root zone.

Continual Misting with Proper “Conditions”

With proper oxygen and temperature ( 62F – 71F ) in the nutrient solution in the aeroponic growing chamber, the plant root system will not become water logged or root rot problems. The plants root system on continual misting cycle will produces extremely healthy roots and high yields of plant material. Continual misting eliminates the problems of roots drying out between misting cycles and is one way of ensuring temperatures in the root zone stay stable and do not fluctuate.

The Need for Tweaking

Aeroponic timers allows the grower ability to adjust the frequency of the on/off misting or spraying cycle as well as how long the roots are misted for. FHD has discovered that by changing the cycle timer during the plant stages of life, we received overall better production without adding higher cost in the systems. This idea is based on applying more oxygen to the root system than continual misting cycle. When using this type of system the following points should be taken into account.

1. There is not one set ideal misting program, the amount of nutrient mist time required, is largely depended on the plant, stage of development and more importantly the temperature in the root chamber during the plant stages.

2. Each growing environment is different. The need for experimenting is crucial in receiving eXtreme harvest. Take your time, set your timer 1 minute on and 1 minute off. Then watch the program in action allowing to repeat its self a few times making sure the plant leaves don’t start to wilt from lack of nutrient mist. If no sign of wilting, increase off time for a minute. Continue until desired setting is reached or 10 minutes is reached. Repeat this programming once a week for that growing week. Ultimate would be 1 minute on and 2 minutes off, for first 2 weeks of vegetative stage. Then moving to a 1 minute on and 3 minutes off after shading the growing chamber and the whole duration of flowering a 1 minute on and 10 minutes off.

4. The major benefit of an adjustable misting program is its flexibility in the growing stages of the plant. When propagated in an aeroponic chamber, newly clipped clones need to be constantly misted until rooted with a dome on top to trap humidity to the plant leaves. Once rooted, the root system needs nutrients. The nutrient interval cycles are determined in vegetative and flowering stages by root temperature. As the plant matures, the plant leaves will begin to shadow the growing chamber, reducing temperature, allowing decreasing misting time. By utilizing this procedure, the plant is allowed more oxygen intake to the root hair between feedings, achieving faster and bushier growth. In flowering, the importance of oxygen intake to the root system is staggering. Plants will go from looking beautiful to looking sick and death is inevitable from oxygen starvation.

5. Always keep a close eye on the root system inside an aeroponic chamber – even slight drying of a portion of the root system will result in tissue damage and could lead to pathogen attack.

6. Make sure to use a quality sediment free nutrient, as it’s very important not to have a mister plug up. Remember that in aeroponics, the ppm (EC) in the nutrient solution needs to be less concentrated, than other soil-less systems as the roots intakes the nutrients much more easier.

Nutrient Uptake – Day and Night

Most plants take up nutrients by both day and night. With night time being the more dominant side. Commercial hydroponic growers of ‘heavy feeder’ crops such as cucumbers and tomatoes, experience higher nutrient uptake in the evening and into the night as the temperatures cool down the plants are able to take up more water and nutrients through increased root pressure and more suitable environmental conditions. Warmer conditions during the day, the plant will shut down photosynthesis and transpiration and thus reduce nutrient uptake, and will then feed rapidly in the evening as conditions become cooler. Calcium is taken up during the night when root pressure allows more water uptake and transpiration within the plant, carrying with it calcium into plant tissue.

The Root System

Plant roots, which end up continually submerged in a ‘deep flow’ or constant drip systems will commonly be long, thin, relatively unbranched, yellowing or brown in color and seem to be lacking in fine, fluffy root hairs. The roots which develop up above the flow or pond of nutrient with a mist are typically whiter in color, more branched out and often contain masses of very fluffy, fine, bright white root hairs.

Oxygenation, Air Pumps, Nutrient Uptake and Temperatures

Introduction: Why plant roots need oxygen

Oxygen is an essential plant nutrient – plant root systems require oxygen for aerobic respiration, an essential plant process that releases energy for root growth and nutrient uptake. In many ‘solution culture’ hydroponic systems, the oxygen supplied for plant root uptake is provided mostly as dissolved oxygen (DO) held in the nutrient solution. If depletion of this dissolved oxygen in the root system occurs, then growth of plants, water and mineral uptake are reduced.

Injury from low (or no) oxygen in the root zone can take several forms and these will differ in severity between plant types. Often the first sign of inadequate oxygen supply to the roots is wilting of the plant under warm conditions and high light levels. Insufficient oxygen reduces the permeability of the roots to water and there will be an accumulation of toxins, so that both water and minerals are not absorbed in sufficient amounts to support plant growth. This wilting is accompanied by slower rates of photosynthesis and carbohydrate transfer, so that over time, plant growth is reduced and yields are affected. If oxygen starvation continues, mineral deficiencies will begin to show, roots die back and plants will become stunted. If the lack of oxygen continues in the root zone, plants produce a stress hormone – ethylene, which accumulates in the roots and causes collapse of the root cells, at this stage pathogens such as pythium can easily take hold and destroy the plant.

Oxygen in Hydroponic Nutrient Solutions

While it’s possible to measure the levels of dissolved oxygen in a hydroponic nutrient solution, it’s not carried out as often as EC and pH monitoring due to the cost of accurate DO (Dissolved Oxygen meters). However, if an effective method of aeration is continually being used, and solution temperatures are not reaching excessively high levels, then good levels of oxygenation in most systems can be achieved One of the most common and effective methods of oxygenation in hydroponic nutrient solutions is with the use of air pumps/machines and air stones.

Air Pumps and Air Stones

While there are a number of methods that can be used to introduce oxygen into a nutrient solution, many of these, such as ozone treatment, are expensive and not often used by smaller growers. One of the most practical and inexpensive, yet efficient ways of getting more dissolved oxygen into a plants root system is through forcing air into the nutrient. Air pumps are widely available in a range of sizes, from very small up to very large with capacity to run from one to many `air stones’ each introducing hundreds of tiny bubbles of fresh, oxygen rich air into the nutrient solution.

Why an Air Stone

While an air pump tube alone can bubble air into a nutrient solution, oxygenation or the process of getting atmospheric oxygen dissolved into the liquid nutrient, is much more effective where many tiny bubbles of air are created, rather than a slow stream of larger bubbles. The greater the surface contact between the air bubbles and the nutrient, the more oxygen will diffuse into the nutrient solution and smaller bubbles create a far greater surface area than a few larger bubbles will. Air stones simply break up the air flow and distribute along the surface of the porous ‘stone’ so that many tiny bubbles are rapidly introduced into the nutrient. Depending on the size or dimensions of the nutrient reservoir into which air is being introduced for oxygenation, air stones of different shapes and sizes can be selected. For small rectangular tanks, long thin air stones (some up to 1 foot in length) can be placed on the base of the reservoir to distribute air bubbles and oxygen uniformly. A larger number of smaller, round, cylindrical or oval air stones placed at equal distance inside a nutrient pool or tank also ensure high levels of oxygenation.

Air stones also have the benefit of acting as ‘weights’ which remain stable on the base, or in the lower layers of the nutrient tank – the further the bubbles have to travel to reach the surface of the nutrient, the more time oxygen has to diffuse into the liquid and the higher the rates of dissolved oxygen than can be obtained from an air pump and stone set up.

For systems with multiple nutrient reservoirs or tanks, one large air pump with many outlets will allow oxygenation into all systems and it is always a good idea to buy an air machine and air stones larger than currently required so that aeration can be increased under warmer conditions or if the hydroponic system is later expanded.

Oxygen and Temperature Effects – Effective Aeration

While forcing air bubbles deep down into the nutrient reservoir generally increases the dissolved oxygen levels in the nutrient, there is one other major factor to consider and that’s the temperature of the air being pumped into the nutrient. As the temperature of a nutrient solution increases, its ability to hold dissolved oxygen decreases. So a cool nutrient solution may in fact hold twice as much oxygen at ‘saturation level’ than a warm solution. For example a nutrient solution at 45 F can hold around 12ppm of dissolved oxygen at ‘saturation’, (meaning it is the most it can hold), but the same nutrient solution at a temperature of 85 F will hold less than 7ppm at saturation. This means at a solution temperature of 85F there is much less dissolved oxygen available for the plant’s root system to take up. To complicate matters further, the requirement of the plant’s root system for oxygen at warmer temperatures, is many times greater than at cooler temperatures due to the increased rate of root respiration. So warm nutrients mean a very high oxygen requirement from the plant’s roots, but the nutrient can only hold very limited amounts of dissolved oxygen at saturation, no matter how much air is being bubbled into the solution. Ideally, nutrient solution temperatures for most plants should be run lower than the overall air temperature – this has many beneficial effects on plant growth and development. However, if overly warm air from the growing environment is pumped into an otherwise cool nutrient solution, the warm air will rapidly increase the temperature of the nutrient to that of the growing environment. If air is being pumped via an air machine with an intake close to lights or other heat sources then rapid heating of the nutrient will occur. On the other hand, cool air has the ability to reduce the temperature of the nutrient if sufficient levels are pumped in and thus result in a much more highly oxygenated solution for the plant’s roots. If keeping the nutrient solution temperature down seems to be a continual problem, checking the air inlet temperature of an air pump is a good idea. Overly warm nutrient solutions (ideally nutrient solutions should remain below 65 – 75 F) for most warm season, high light plants and well below 69 F for cool season.can have serious effects on the plants root system. Apart from the increased oxygen requirement due to a much higher rate of root respiration which can rapidly result in oxygen starvation, high solution temperatures favour many of the root disease pathogens. Plant roots become highly ‘stressed’ when experiencing high temperatures, particularly if there is a large mis-match between the air the root temperature. Root stress slows the development of new roots, resulting in reserves inside the root tissue being `burned up’ during respiration faster than they are accumulated, and stress makes the root system in general more susceptible to disease attack. Keeping a check on nutrient temperature is vital, as is ensuring that air machines are not blasting hot air into the solution and cooking plant roots. Aeration is most effective when cool air is bubbled into a nutrient.

Oxygenation and Nutrient Uptake

Healthy roots supplied with sufficient oxygen are able to absorb nutrient ions selectively from the surrounding solution as required. The metabolic energy which is required to drive this nutrient uptake process is obtained from root respiration using oxygen. In fact there can be a net loss of nutrient ions from a plant’s root system when suffering from a lack of oxygen (anaerobic conditions). Without sufficient oxygen in the root zone, plants are unable to take up mineral nutrients in the concentrations required for maximum growth and development. Maintain maximum levels of dissolved oxygen boosts nutrient uptake by ensuring healthy roots have the energy required to rapidly take up and transport water and mineral ions.

Calcium is one important nutrient ion which has been shown to benefit from high levels of oxygenation in the hydroponic nutrient solution Calcium, unlike the other major nutrients is absorbed mostly by the root growing tips (root apex). The root apex has a large energy requirement for new cell production and growth and is therefore vulnerable to oxygen stress If root tips begin to suffer from a lack of oxygen, a shortage of calcium in the shoot will occur. This shortage of calcium makes the development of calcium disorders such as tip burn and blossom end rot of fruit more likely and severe under oxygen starvation conditions. High levels of oxygenation ensure healthy root tips are able to take the levels of calcium required for new tissue growth and development.


While providing oxygenation with the use of air machines and stones is an excellent method of increasing the dissolved oxygen (DO) levels in a nutrient solution, the temperature of the air intake and nutrient solution must also be managed to ensure oxygen starvation in the root zone does not occur. Pumping hot air into a nutrient not only creates temperature stress in the root zone, it also results in less oxygen carrying capacity in the solution itself – a recipe for root suffocation that will rapidly affect the top portion of the plant as well. Getting oxygenation right means checking both aeration capacity of the equipment being chosen and temperatures in the nutrient and root zone.

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