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Introduction to the Root Zone
Plant roots are arguably the most important part of a plant, and are also one of the most easily damaged. Root problems and disease are the most common source of problems for growers. If you want to maximize the the health and ultimate yield of your plants, it is wise to have a clear picture of the crucial activites going on at the root zone.
Roots are made up of tough, fibrous tissues containing cellulose, hemicellulose, and lignin which branch into the soil mass (or grow media,) anchoring a plant firmly. Their basic functions are critical for plant survival: they absorb water, oxygen and minerals, and they conduct these to where they are needed. With a strong and healthy root zone, plants are able to access what they need for vigourous growth. Without a healthy root system, your plants are doomed to be weak and spineless, or even worse, dead.
A healthy root zone is a continuously growing one. In many plants this cycle includes the natural death of older roots and the production of new ones. This cycle of death and regeneration is often mistaken by growers as a sign of disease, but so long as there are new roots developing, some root death should not be a concern.
Root Zone Health and Color
A young plant root system should have lots of white furry root tips everwhere. A healthy mature root system will be strong and fiborous and will have a thick root mat. If the roots are cream or yellow on top of the mat, they should still have many white root tips underneath at the bottom.
Thick, fat, white furry roots are what you most want to see - they are absolutely indicative of healthy root growth. Be aware however that the color of a nutrient solution will stain the roots, turning them yellow or brown. This is also true of many nutrient additives. Older, more mature plants will have a darker cream-colored root system, and some plants just tend to have a natural color pigment.
Root Zone Temperature
The temperature of the root zone and the temperature of the nutrient solution can have a major effect on the healthy growth and appearance of the root system. In general the temperature should be between 68 and 72 degrees farenheit. Colder or warmer conditions can cause poor and stunted root growth, as the roots don't want to grow into the unhospitable nutrient solution. Major root death can occur in even brief periods of cold or heat stress. Poor temperature conditions leave the door open to root disease.
Oxygen at the Root Zone
Lack of oxygen at the root zone is the leading cause of root death. Roots NEED oxygen. Roots should never sit in stagnant or ponding nutrient solution - make sure the trays are tilted and supported to drain completely. Lack of oxygen can also be caused by decomposing organic material in the nutrient solution or trays - this material should always be removed. . Another problem can be too many plants competing for too little oxygen. These problems are worsened by high root zone temperatures.
Nutrient reservoirs should always be aerated by and air pump and air stone. You can never have too much oxygen, so the more and stronger air pumps used, the better. We have had great succes adding air stones to the growing trays themselves, to supplement the root zone area with addtional oxygen. Some growers use H202 to add additional oxygen, as well.
EC/ TDS & pH
A nutrient strength level that is too high can be toxic to the root zone and will cause poor and stunted growth. At extreme levels, a too high level will cause actual death in the root zone. It is best to increase nutrient levels gradually over time rather than suddenly and all at once.
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Root-Microbe Symbiosis
The root zone of a plant is buzzing with life-essential processes of incredible complexity. This zone of intensive activity is called the rhizosphere. The root itself makes up part of the rhizosphere (the endorhizosphere), while the root hairs, mucigel, and root cells that have sloughed off constitute the ectorhizosphere.
The plant actually grows its own garden of microbes, along the root surfaces. To do this, the light energy captured from photosynthesis in the leaves is channeled down the stem through the phloem vessels and out through epidermal cells to the external root surface. Incredibly, up to 80% of the total plant energy--but usually 12 to 40%--is exuded as mucigel into the ectorhizosphere as carbohydrates, amino acids, and other energy-rich compounds. As the roots grow, the roots slough off dead cells which form a slimy covering and help the roots to slide easily as they grow. This slime is a food source for many millions of beneficial microbes. This food doesn't stay around long. Billions of bacteria, fungi, algae, actinomycetes, protozoa, and other microbes feed upon this exudate.
Those Phenomenal Mycorrhizae
Especially important are the mycorrhizal fungi which extend their thread-like hyphae from inside cortex cells out into the soil for several millimeters. They extend the feeding volume of the root by 10 to 1,000 times or more for most plant species (the cabbage family being a notable exception), and extract and carry nutrients back to the root. So important are they that scientists sometimes call the root zone the mycorrhizosphere. Pine trees will hardly grow without these fungi. There are two types- ectomycorrhiza and endomycorrhiza. Ectomycorrhiza are found in association with forest trees such as pines, eucalyptus and dipterocarps, while endomycorrhizal associations are formed in horticultural, forest and agronomic crops
Feeding On Exudate
In return for the release of nutritional substances from plant roots, microbes themselves produce chemicals that stimulate plant growth or protect the plant from attack. These substances include auxins, enzymes, vitamins, amino acids, indoles and antibiotics. These complex molecules are able to pass from the soil into plant cells and be transported to other parts of the plant, with minimal change to chemical structure, where they can stimulate plant growth and enhance plant reproduction. They may also play a role in enhancing the nutritional composition of the plant. The types of molecules released are specific for a variety of plants grown under certain conditions, forming in effect a unique chemical signature. As these molecules are released into the rhizosphere, they serve as food and growth stimulants for a certain mix of microbes.
The USDA Agricultural Research Service, and other scientists have shown that for each plant species, this characteristic chemical soup stimulates the development of a select, beneficial company of root-dwelling microbes. This microbial population colonizes the root zone, producing certain chemicals that inhibit the growth of pathogenic species. These organisms are also instrumental in supplying the plant’s unique nutritional needs .
The rhizosphere is always functioning for the plant whether it is growing in a field, in a pot, in a hydroponic media, or even in a lake or ocean. The details of function may differ somewhat, but the principles are the same in order for the plant to survive.
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Some of the main Beneficials at the Root Zone
Bacillus
Several varieties of Bacillus (i.e Bacillus megaterium) have been found to play a role in the conversion of unavailable forms of phosphates into plant available forms. In natural settings they can provide near 10% of the available phosphorous in the soil solution. With increased levels of plant available phosphorous, Bacillus strains become less effective. However, if the Bacillus can sustain as a back up it may continue to provide hungry blooms with phosphorous if it should become otherwise unavailable or “locked out”. This bacterium is of special interest to organic farmers who incorporate rock phosphate into the growing medium or if introduced through fertilizer teas, preparations, etc. Rock phosphate tends to be mostly unavailable, breaking down into plant available forms over time.
Certain forms of Bacillus are known to inhibit pythium and other pathogens. One of these is bacillus subtilis and is found in Hydroguard .
Mychorhizal Fung
Mycorrhizal fungi are especially effective in providing nutrients to plant roots. These are certain types of fungi that actually colonize the outer cells of plant roots, but also extend long fungal threads, or hyphae, far out into the rhizosphere, forming a critical link between the plant roots and the soil. Mycorrhizae produce enzymes that decompose organic matter, solubilize phosphorus and other nutrients from inorganic rock, and convert nitrogen into plant available forms. They also greatly expand the soil area from which the plant can absorb water. In return for this activity, mycorrhizae obtain valuable carbon and other nutrients from the plant roots. This is a win-win mutualism between both partners, with the plant providing food for the fungus and the fungus providing both nutrients and water to the plant. The importance of mycorrhizae in plant productivity and health has often been overlooked.It has been well documented that mycorrhizal plants are often more competitive and better able to tolerate environmental stress.Mycorrhizal technology has likewise made possible the production of inoculants to significantly improve the survival, growth and establishment of trees and crops.
M y•cor•rhi•zal - The symbiotic association of the mycelium of a fungus with the roots of a seed plant.
Nitrosomonas Bacteria
Species of aerobic bacteria which converts ammonia to nitrite. One of the critical bacteria in nitrogen cycle. Optimum pH range between 6.0 and 9.0, temperature 10oC - 34oC. Will acclimate to changes in water quality, but activity is reduced during acclimation which can lead to a build up of ammonia.
Nitrosomonas eat ammonia, they absolutely LOVE it. They Convert plant available ammonium (NH4) to unavailable nitrite (NO2).
Nitrobacteria
These bacteria convert the nitrite (NO2) resulting from the nitrification above into nitrate (NO3-), an important form of Nitrogen that all plants need.
Streptomyces
Bacteria that secrete a variety of compounds including antibiotics that prevent and control root zone pathogens. A closely related species of Streptomyces produces the antibiotic that we use, streptomycin. Many studies demonstrate the bacteria’s effectiveness at controlling root diseases, and select foliar diseases. An interesting consideration noted in one study is that they will also reduce levels of some nitrogen fixing bacteria in the soil.
Trichoderma
Some species of fungi that parasitize other fungi, such as Trichoderma, have been observed physically attacking and destroying pathogenic fungi. Strains of Trichoderma are found naturally occurring in many soils can play a role in the prevention and control of root pathogens, ultimately providing a healthier soil environment which can lead to higher yields. Some research suggests that the proteins in Trichoderma can degrade chitin, which is a structural component found in pathogenic fungi such as powdery mildew and in insects.
Some innovative propagation materials are inoculated with strains of Trichoderma.Many forms of coco coir contain it naturally. CANNA's Coco Growing Media is innoculated with it. If a healthy root environment is maintained, the bacteria will continue to colonize the roots and multiply in the growing media. The trichoderma help to form a protective layer around the root system, helping to fend off invading pathogens, etc.
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Root Health and Pathogen Control
In hydroponics we can promote a plant's rhizosphere capability by insuring it has the proper minerals, as well as a well aerated root zone to allow for good air and water movement . We also suggest using an organic amendment like Liquid Karma as well as a general enzymatic product like Hygrozyme or SensiZym from Advanced Nutrients that will encourage the proliferation of healthy rhizosphere microbes. You may also wish to use a root stimulator / stress reliever like CANNA Rhizotonic. It is a powerful, organic stress-reliever which stimulates new root development, increases resistance against disease and improves the vigour of plants.
Most root pathogens seem to be opportunistic -that is, they take advantage of weak and/or damaged roots. Thus the best defense is to keep roots healthy in the first place. In the beginning of this FAQ we went over some of the basics, those being temperature and oxygenation. We can also add a silica to the nutrient solution such as Silica Blast. Silica has been shown to greatly reduce plant death, root decay and yield losses caused by root disease. It does this by fortifying plant tissues against attack. The disease may still be present, but it is not able to do damage.
It has been found by numerous studies that plant roots colonized by a mixture of different bacterial and fungal species, are far more resistant to pathogenic attack. Mycorrhizal fungi form an impenetrable physical barrier on the surface of plant roots, varying in thickness, density and fungal species, according to the plant species, plant health and soil conditions. Ideally the beneficial microbes out-compete pathogenic species and form a protective layer on the surface of living plant roots. In soil it is usually only when the beneficial species of bacteria and fungi are killed by continuous soil disturbance and toxic chemicals that pathogenic species have an advantage.
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Using Good Microbes to fight the Bad Ones
There are a slew of new beneficial microbial products on the market, and they have a variety of effects ranging from breaking down nitrogen into useable forms to cleaning the roots to warding off negative microbiological pathogens. These good microbes also activate, enrich and stimulate the roots - they help to create beautiful fuzzy white root growth like you have never seen before.
The new array of products on the market can be confusing an misleading. We only sell products that we are familiar with and have personal experience with. Here are some of what we think are best.
Earth Ambrosia / Earth Nectar: a two-part mycorrhizal fungi innoculant - in liquid form
Down to earth mycorrhizal root innoculant: in powdered form for soil or coco
Piranha Piranha colonizes the root zone with 26 beneficial fungi (in powder form for hydro)
Tarrantula Bacterial blend of 57 microorganisms, with 1.4 billion Colony Forming Units per gram
Voodoo juice Liquid solution consisting of five strains of bacterial microbes, one is a nitrogen fixer
Botanicare Hydroguard Water treatment and pathogen supressor made of four benefical bacteria: Bacillus subtilis, Paenibacillus polymxa, Bacillus circulans, and Bacillus amyloliquefaciens.
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The Other Route: Keeping the Reservoir Sterile
Some would argue that one of the strengths of hydroponics is its sterile environment, and the notion of exposing growing systems to bacterial and fungal organisms would be self-defeating, if not sacrilegious. These growers rely on sterile growing environments, strong disinfectants and a product like SM-90. Another option is Hydrogen Peroxide. Each of these offer their own protection and benefits. But NEITHER SM-90 or Hydrogen Peroxide works well with organic aditives in the reservoir. They do not work well together and SM-90 has also been known to react poorly with Superthrive.
In a sterile growing environment, your goal is to have a super clean reservoir. This is harder than it sounds. Folks who have been growing in the same area with the same equipment for years might find that they are suddenly having root problems when they never had them before. Or a new grower might begin having problems right from the beginning.
Keeping your reservoir totally sterile can work very well, but once you get a population of icky badness it will keep coming back again and again. Some pathogens such as pythium are almost impossible to get rid of completelely. No matter how many times you sterilize everything with a bleach solution, the problem returns. It can get very frustrating and expensive to constanly be battling. More and more innovative growers are moving toward a more wholistic approach of using good microbes in the reservoir.
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Root Rot and Pythium
"Root rot" is a generic name for several common opportunistic waterborne diseases that can seriously affect indoor and outdoor crops year round. "Pythium" is the name of one of these diseases and is also used as a generic term for several different root rot and stem rot fungus species (including Pythium, Verticillium, and Phytophthora, and Fusarium). The term “damping-off” is also often used and usually applies to disease in seeds, seedlings and clones.
Whatever you call them, these diseases attack the roots of a plant and can rapidly infect crops in all stages. Damage includes reduced yields and crop failure. Pythium is particularly damaging in recirculating hydroponic systems as they provide ideal conditions for rapid growth and spread of infectious spores; a single infected plant can breed and send spores to all the plants.
The best thing is to prevent root rot from ever taking hold in the first place. It is an opportunistic disease which means that it is looking for sick, injured or weakened plants. Pythium is almost impossible to 100% eradicate from an infected system; this involves starting completely over (with new parents, containers, equipment, etc). It is probably present even if you don't know it - just waiting for its chance to get in.
“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. “
Dr. Lynette Morgan, Growing Edge Magazine
"Nutrient Temperature, Oxygen and Pythium in Hydroponics"t
http://www.hydromall.com/grower/pyth...droponics.html
How to Avoid a bad case of Root Rot
Monitor plants and roots frequently
Maintain a clean system – change and sterilize reservoir weekly.
Design your system to combat pathogens
keep your nutrient reservoir between 68 and 72F to maximize root growth, Dissolved Oxygen levels and inhibition of Pythium. 80 degrees and above will bring on a fast case of root rot.
Constant aeration – maintaining high dissolved oxygen levels inhibits pathogens and accelerates root growth
keep a lid on your reservoir to keep plant matter and light out
Maintain a low pH of 6.2 or less to inhibit pythium growth
Use prevention!! Use tank additives to give your roots the edge they need to grow strong and healthy!! Check out the Roots and Prevention section.
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Bacterial slime and other horrifying nasties
These are not the beneficial bacteria and fungi that we have already spoken about. These bacteria cause cloudy reservoirs, slimy build up, weird reservoir fuzz, gelatin growths and wild pH fluctuations. These are the reservoir monsters.
When these bad microbes are present at high populations and are happily feeding on organic matter, they use up just about all the oxygen in the nutrient solution, suffocating the plants. They release toxic substances as a biproduct of their life cycle. They also suppress the good microbes at the root zone and cause problems with nutrient uptake and plant growth.
Bacteria slime and cloudy reservoirs
Bacteria can make the water cloudy, but tend to produce more of a slime or jellylike, smelly mass in the system.If you have it, you will notice slimy reservoir walls and perhaps an oily slick on the water. Another symptom can be a foamy buildup in the reservoir. If left to their own devices, these bacterial growths will smother the roots, depriving them of oxygen. Some species of anaerobic bacteria thrive in an environment deprived of oxygen and can produce chemical metabolites, such as alcohols, aldehydes, phenols and ethylene, that are toxic to plant roots and to other microorganisms.
Other symptoms of bacterial infections can be fuzzy, cotton like growths, or the growth of fur. Just in case you are wondering, that white fuzzy growth you see at the tip of your roots is desireable. That is not bacteria - That is the good stuff - you should see tiny fine white hairs at thje roots.
All of these nasties require organic matter to feed on. They may be there as the result of a buildup of dead roots and leaves in the root zone, but usually they are the result of adding an organic product to the reservoir. If the conditions are just right, the bacteria will begin to thrive.
One option is to use no organic additives at all and to rely strictly on chemical nutrients based on fertilizer salts. We think a better choice is to continue using organic material, but also using an enzymatic addtive like Hygrozyme that will break down the unwanted organic matter in the reservoir . If you would like to use additives such as bat guano, compost or fish-based products, you might consider run to waste instead of a recirculating system.
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What to do if you have a bacterial or fungal infection
You will want to completely clean out your system - if you can, you should remove each plant, rinse it off, perhaps even dip it in an H202 solution. You should trim off any dead roots. you should then clean your entire system using a strong bleach or h202 solution. We suggest soaking everything in bleach for a few hours. You will definately want to soak your pump and any tubing in bleach. Make sure you rinse everything very well before putting the plants back in .
If your plants are damaged, you might want to run the nutrient solution at a lower concentration than usual. We highly recommend using an enzymatic addditive such as Hygrozyme (after everything has been cleaned&sterilized ...). . You should also run a stress relief additive like CANNA Rhizotonic. We always suggest using Liquid Karma , but if your problem is real bad, you might want to lay off the organics a little bit.
While your roots are really hurting, you may want to foliar feed your plants with Nitrozime or Dutch Master If you haven't already, you should read the section above about inncoulating your system with good microbes.
Keep an eye on your reservoir. Be prepared to clean it out regularly, as soon as any sign of a infections (cloudy water or wild pH fluctuations) occur.
Remember IT IS MUCH EASIER TO PREVENT a pathogenic attack than it is to ddeal with it once it has occured!
