Mycorrhizal fungal filaments.

The seemingly magical properties of mycorrhizal fungi (aka ‘mycorrhizae’) are already fairly well known to soil growers. This special “root fungus” forms a mutualistic relationship with the roots of many plants, allowing them to access more water and nutrients. Mycorrhizae effectively extend the reach of the roots by forming a mycelial network that is able to extract tightly bonded water and nutrients (particularly phosphorus and iron) and translocate them back to the plant. The plant, in turn, feeds the root fungus with carbohydrates. Everybody’s happy – it’s mutual after all!

Ok, so that’s soil. But what about hydroponics? Nutrient manufacturers remain divided on the issue. Some recommend a completely sterile environment. That means no bacteria (beneficial or otherwise) and no friendly fungi. Why? Proponents of sterile growing environments argue that in hydroponics the grower is supplying all the nutrients their plants need in a directly accessible form and question the need for little ‘fungi helpers’ to assist in nutrient assimilation. (In hydroponics, all the nutrients are supplied in ionic, or directly accessible, form.) Similarly, the roots shouldn’t have to go out in search of water in hydroponics as it’s being provided in abundance. However, recent studies have shown that mycorrhizae can help plants uptake mineral-based nutrients too, promote with root branching, and massively extend the active feeding capacity of the feeder root tips.

Sound interesting? We thought so! So we asked mycorrhizae experts Mike Amaranthus PhD and Josh Eagan BS to give us the low-down on how this special root fungus behaves in a non-soil environment.

Modern hydroponic growers sacrifice too, increasingly by sacrificing plant quality and profits to prevent damage from a host of fungal “fiends” with names like black rot, club root, sclerotina blight, wire stem, sudden death syndrome, brown spot, and charcoal rot. Opportunities for using beneficial fungi as “friends” exist for the grower as well. The best documented friendly use is mycorrhizal fungal inoculum for improving plant nutrient uptake, plant quality, yields, and disease resistance.

THE FUNGUS FIEND

Most growers blame their nutrients when things start going horribly and unexplainably wrong. Big mistake! Pythium and phytophthora are two of the most common fungal diseases that can affect indoor growers, and they are not easy to spot until well advanced. Pythium-caused root rot is a real problem in hydroponic systems and is becoming increasingly common.

Pythium-infected Hosta plant.

Pythium is a waterborne fungus and recirculating hydroponic systems provide it with an ideal environment in which to live and breed. Plants can survive and grow with high levels of pythium spores in the nutrient solution. The fungus, however, will restrict the root system. A sudden rise in temperature will find the plants unable to increase their uptake of water and they will wilt. For many growers this is the first sign that pythium is active in their system. Damping-off caused by pythium affects growers growing in flats or in the propagation of cuttings. Damping off can attack and topple plants in just a few days. The lower stem becomes constricted and dark brown near the growth media’s surface, a symptom called wire-stem. The hydroponic grower can encounter pythium at any time and, if he is unprepared, he may well lose his crop. Pythium root rot can be caused by several different species of the fungal genera pythium.

Phytophthora, the notorious fungus that caused the Irish potato famine, causes annual crop losses in the tens of billions of dollars today. Beginning in 1845 and lasting for six years, the potato famine killed over a million men, women and children in Ireland and caused another million to flee the country. Phytophthora, from the Greek phytón (“plant”) and phthorá (“destruction”), is literally “the plant destroyer” that continues to plague a wide variety of crops globally with no effective means of chemical control.

Certain fusarium fungal species are also among the most dangerous root diseases in the world affecting hydroponic growers. There has been a dramatic increase in fusarium infection in the last several decades. The ability of this disease to form toxins that are poisonous to both humans and animals makes it a serious problem. The most visible symptom of these fungal diseases is in the root systems. Roots will begin to go brown and lose their healthy white appearance. As the pathogen spreads, the roots become soft and mushy and there is always a tendency for the plant to wilt in the warmer part of the day.

THE FUNGUS FRIEND

We can never purge the world of fungus, of course; nor would we choose to. Fungi represent a kingdom unto themselves, the fifth kingdom in fact. As a taxonomic dominion, kingdom is as high as it gets; animals, plants, bacteria, protists and our fungal friends make up the five.

Some 100,000 species of fungi have been described scientifically, and experts estimate that over a million remain to be discovered. Fungi have influenced our life in ways we take for granted. For a loaf of bread and a jug of wine we can thank the fungus saccharomyces, which is used in bakers’ and brewers’ yeasts. For recovery from infection we can thank the common soil fungus penicillium. Serendipity often leads to fungal discoveries. When Alexander Fleming discovered penicillin, he was trying to perfect an antiseptic formula based on nasal mucus. The nasal mucus formulation never did materialize (we can all breathe a sigh of relief!), but his unforeseen discovery of antibiotics changed the world.

What a difference a little mycorrhizal fungi makes! The tomato plant on the left was grown without mycorrhizal fungi, whereas the plant on the right was inoculated with mycorrhizal fungi.

Fungi also have a flair for symbiosis, for establishing cross-kingdom relationships that feed the fungus sugars while bestowing upon its partner new powers. Under natural conditions plants live in close symbiotic association with a group of soil organisms called mycorrhizal fungi. These fungi colonize plant roots and extend the root system into the surrounding soil. Estimates of amounts of mycorrhizal filaments present in growth media associated with plants are astonishing. Several miles of filaments can be present in less than a thimbleful of soil.

The relationship is beneficial because the plant enjoys improved nutrient and water uptake, disease resistance, and superior survival and growth.

It is this not-so-glorious association between plants and mycorrhizal fungi that keeps the whole show rolling in natural environments and can be an important tool for hydroponic growers. Approximately 90 per cent of all land plants depend on the mycorrhizal fungi that radiate from their roots and feed humbly on their plant sugars. In return, the fungus delivers nutrients to the plant like phosphorus, calcium, nitrogen, iron and life-giving water.

The mycorrhizal relationship is ancient and fundamental. In fact, in natural habitats, the presence of mycorrhizal fungi on the roots of plants is as common as chloroplasts to the leaves of plants. Botanists believe that plants might never have made the leap onto land some 460 million years ago without the assistance of Robigus and his mycorrhizal assistants.

This mutually-beneficial association between fungus and plant provides the fungus with relatively constant and direct access to carbohydrates, such as glucose and sucrose produced by the plant in photosynthesis. The carbohydrates are transferred from plant leaves to the root tissues and then to the fungal partners. In return, the plant gains the use of the mycelium’s very large surface area to absorb water and mineral nutrients from the soil, thus improving the mineral absorption capabilities of the plant roots. Mycorrhizal mycelia are much smaller in diameter than the smallest root, and can explore a greater volume of soil-less media, providing a larger surface area for absorption. Also, the cell membrane chemistry of mycorrhizal fungi is different from that of plant roots. The whole length of the mycelia is capable of absorption as compared to just the tips of the roots themselves. Plants grown in sterile soils and growth media often perform poorly without the addition of spores or “propagules” of mycorrhizal fungi to colonize the plant roots and aid in the uptake of soil mineral nutrients.

These mycorrhizal fungi are the best understood of the soil microbe families—and potentially the most useful to growers. Nearly all important crops form the mycorrhizal relationship, with notable exceptions including the mustard family, canola, broccoli, and sugar beets. Mycorrhizae attach themselves to plant roots and grow thread-like hyphae out into the surrounding soil, siphoning amino acids, nutrient molecules and water back to the plant. A grower benefits from mycorrhizal inoculation as it increases the effectiveness of added fertilizer and protects the root system from fungal fiends.

How do mycorrhizal fungi protect roots? The source of disease resistance is probably a combination of factors. The mycorrhizal fungus can present a physical barrier to the pathogenic fungus and/or produce antibiotics that limit the growth of the pathogen. Also, mycorrhizal-colonized plants develop more robust root systems that buffer the plant against the impact of pathogens.

It is also possible that the mycorrhizal fungus stimulates the host to produce chemicals that inhibit the growth of any other fungus on the root. In addition, because the mycorrhizal fungus is so adept at capturing nutrients, there are limited resources available for the growth of the disease fungus. Research has shown that, once a root is colonized by a mycorrhizal fungus, it is more resistant to infection by disease organisms.

INVITING A FRIEND TO DINNER

How do you inoculate mycorrhizal fungi to a hydroponic growing operation? Certain mycorrhizal spores (or “seeds”) of the fungus have been selected for their growth-enhancing abilities. The goal is to create physical contact between the mycorrhizal inoculant and the plant root. Generally, mycorrhizal application is inexpensive and requires no special equipment. Growers have at least three options to inoculate with mycorrhizal fungi.

Powder, liquid and granular forms of mycorrhizal inoculum.

The first method is an incorporation of a granular or powder form of the mycorrhizal inoculant into the growing media before planting. Secondly, the granular or powder inoculant can be placed into soil or soil-less mixes before placing the transplant into the planting hole, or distributed around the root ball after placement. The third option is a water-in drench. A powder is mixed with water, or a liquid is injected into the rooting zone through existing spray devices. In all three methods, all that is needed is for the mycorrhizal inoculant to reach the vicinity of the roots.

Fungi are omnipresent, occupying every ocean, the atmosphere, and the soil on every landmass. While some fungal fiends are “killers,” attacking living tissue they have infested, the vast majority are benevolent and, in many cases, vital to life forms around them. Fungi can be both fiend and friend to the hydroponic grower. While fungal diseases can impact the grower’s bottom line, mycorrhizal fungi can improve hydroponic yields and be a low-cost, natural solution to increasingly expensive chemical and disease control treatments. Certainly, using beneficial fungi in a hydroponic operation is a preferred alternative to the sacrifice of dogs and cows with rust-colored fur to Robigus!

Check out Urban Garden Magazine’s handy-dandy Mycorrhizae Q&A!

Got a question about mycorrhizae that we didn’t answer? Give us your best shot: post your question or comment below!

Everest shares some time-honored heuristics to help beginner growers increase the productivity of their indoor gardens.

1.) Reduce Your Concentration!

Hydroponic growers adjust the pH of their nutrient solution to around 5.8 to 6.2 – this provides the best accessibility to the widest range of nutritional elements.  pH adjuster products are sold in grow stores in concentrated liquid (sometimes powder) form.  However, some growers get lazy and add this stuff neat (undiluted) to their nutrient solution.  This causes nutritional elements to precipitate out of the solution and therefore become unavailable to your plants.  To avoid this, make up a dilute solution of your pH adjusters – 1 part pH adjuster to 100 parts water – and use this instead.  The weakened concentration of your pH up or down will enable you to safely adjust the pH of your nutrient solution without damaging your nutrients!

2.) So Near, So Far …

More light = more yield … but only to a point!  In fact, grow lights can represent a mixed blessing for the indoor gardener.  Sure, they provide the all-important light photons essential for photosynthesis – your plants ain’t growing without them!  But these same lamps also generate a lot of radiant heat!    If your plants grow too close to your lamps they will become too hot and shut down (stop photosynthesizing).  In extreme cases they will scorch and burn and the growth tips will die.  This causes untold stress to your plants and drastically reduces your yields.

On the other hand some growers are overly cautious and raise their grow lights too high, causing their plants to stretch in search of more lumens.  The ongoing aim of every indoor gardener is to get as many growth tips in the “sweet spot” as possible.  This is the area where your plants are just at a safe distance away from your bulbs and receiving maximum light intensity.

Different growers combat this problem in different ways.  All growers should try to move the air in between the tops of their plants and the lamp using an oscillating fan.  Some growers also air-cool or water-cool their grow lights while some put their lights on a mover or spinner.

As well as a light meter, use a thermometer with a remote temperature probe to measure the heat at the tops of your plants.  For many popular indoor crops, the magic number is 82°F (28°C).  What’s the temperature reading at the top of your plants?

3.) Brrrrr!  Using Cold Tap Water!

First off, tap water can contain chlorine and chloramines plus high levels of other minerals (often not in a form that is useful to your plants) and other impurities.  You should always feed your plants with the best quality water you can.  Many professional growers and keen hobbyists take control over their water quality by investing in a water softener and reverse-osmosis water purifier.  Also, you should always make sure that the temperature of your nutrient solution is around 65 – 68°F (18 – 20°C) before feeding it to your plants.  Cold water shocks your plants’ roots and warm water contains drastically lower levels of dissolved oxygen.  If your indoor garden is suffering from high temperatures, using a slightly cooler nutrient solution can help your plants get through until you manage to correct your environment.

4.) Lights++ Environment–

So, you’ve managed to dial in your indoor growing environment with two, three or four lights and you’re growing healthy, happy plants and enjoying regular crops of your favorite veggies all year round.  Great, but don’t make the mistake of thinking you can expand by simply adding more lights!   You need to also consider how this will effect your growing environment.  Firstly, more plants will mean more transpiration, and a need for more CO2.  More lights equals more heat to get rid of.  So if you are thinking of adding more grow lights, make sure you budget for increased air transfer too – you’ll definitely need it!

5.) Unruly Plants

A crucial skill that every indoor gardener needs to learn is how to shape and train their plants so that they make the most of any artificial light source.  You need to let your plants know who’s boss.  Do not grow your plants too large.  Small to medium sized specimens are the way forward for most indoor growers.  Remember, your plants receive exponentially less light the further they are from the lamp.  As most gardeners light their plants from above, a common goal for many indoor growers is for shorter, squatter plants with wide canopies.  Think of a candelabra.  Pruning out the leading growth tip will encourage many types of plants to adopt this formation.

TIP:  If you are growing plants that are sensitive to photoperiod bear in mind that they will not respond immediately when you change your light cycle to induce flowering.  Growers of many plant varieties are often stunned by the amount their plants bolt (or stretch) after changing the day length simulated by their grow lights.  Err on the side of ‘small’ when deciding when to switch your plants from vegetative to flowering mode!

6.) Grow Like A Gardener, Not a Robot

So you think you’ve got your nutrient recipe down and now it’s just a question of making it happen.  But the best growers are always in a state of flux.  They are observing their plants on a daily basis, getting in among them, looking for signs of under / over fertilizing and adjusting their nutrient regimen accordingly.

This is especially important if you are making any chance, whatsoever, to your growing environment.  Improved air exchange or CO2 levels in your indoor garden will cause your plants to grow more vigorously.  The saavy grower observes and recognizes this and increases the strength of his nutrient solution accordingly.

Conversely, if the ambient temperature inside your indoor garden rises above optimum levels (e.g. during the summer months) your plants will inevitably use more water.  You should therefore decrease the strength of your nutrient solution.

7.) Stale Food

Re-circulating your nutrient solution?  Great – you’ll save on precious water resources, not to mention expensive nutrients and additives!  But ask yourself – how often do you really drain your reservoir, then rinse, and replenish with a fresh batch?  Once every week?  Once every two weeks?  Or once every … when you can be bothered?  Younger plants will tolerate less frequent nutrient solution changes than more mature plants.  But if you’re really going to turn on the charm, the time for super frequent nutrient solution changes is during flowering and fruiting.  This is when your plants’ nutrient requirements are at their highest and will benefit most from regular nutrient solution changes.

8.) Poor Propagation

Care early on pays massive dividends later.  Be especially patient and watchful during the propagation stage.  Give your plants time to establish healthy root systems before rushing them into a hydroponics system and flowering them off.  Ensure humidity levels are kept fairly high at 60-80%, especially early on.  This reduces stress on the young plant which, in turn, allows it to focus on that all-important root system.

A plant that has been “hardened off” for five or six days under a fluorescent veg lamp, for instance, still needs to be introduced to a 1000W metal halide with care.  Raise the metal halide 3-4 foot above the plants until you see the first signs of growth.  Break those babies in slowly.  What is often diagnosed as “transplant shock” is often more due to the shock of an increase in light intensity.

9.) Lack of Oxygen

Dissolved oxygen in your nutrient solution is so important we can’t harp on about it enough.  Oxygen in your nutrients promotes root health and speeds up your plants’ metabolism meaning it can grow faster and bloom copiously!  Lack of oxygen in your nutrients, on the other hand, invites all sorts of problems, the leader of the pack being pythium which can destroy your crop in a matter of days.  You can increase levels of dissolved oxygen in your nutrient solution by bubbling air into it – the smaller the bubbles, the better!

10.) Don’t Be a Dirty Sanchez

What’s that carpet still doing in your indoor garden?  Is that decomposing plant matter in the corner over there?  Still not got rid of that bag of old root balls from last crop?  Get a grip on your garden!  Clean as you go.  Keep it as spotless as possible.  Filter all air vents.  Think of your indoor garden as a laboratory and you won’t go far wrong.  The cleaner your growing environment, the fewer viruses your plants have to fight; the more energy your plants can put into their primary mission – growing and blooming!  Cleaning sounds boring, and it is.  But how boring is 10% more yield?  Nuff said.

The glorious coconut has been providing us with much more than the odd Piña Colada for centuries. Traditionally, coconut coir (the outer fibrous husk) has been the backbone of “Welcome” doormats, brushes, sofa stuffing and horticulture for well over 100 years but, as far as hydroponics is concerned, coco coir started to make a name for itself during the late ’80s and early ’90s as a substitute for peat and rockwool, both non-renewable resources. In a nutshell (sorry, couldn’t resist), coconut coir is an environmental by-product of the long-established coconut industry. It’s a 100% renewable resource and the environmentally friendly alternative to bog dredged peat moss.

So what is it about coco coir that makes it such a popular replacement for peat and as a hydroponic medium in its own right? Firstly, check out its outstanding water and air holding capacity. Unbelievably, coco coir can hold eight to nine times its own weight in water! More importantly, coco coir holds a lot of air, in fact even when saturated it typically still holds around 22% air. In this respect it is superior even to rockwool, the world’s most popular hydroponics medium. Rockwool is a great medium but some beginners can easily run into trouble as it typically only holds around 10% air, leaving plant roots in danger of becoming oxygen deprived, particularly when the nutrient solution temperature is over 68-72°F (20-22°C). (The warmer a nutrient solution is, the less dissolved oxygen it can hold.) With coco coir, however, this type of overwatering (or, to put it more precisely, oxygen deficiency in the root zone) is avoided by the enormous amount of air that good quality coco coir can hold.

The amazing properties of coco coir don’t end with excellent water and porosity. Oh no! The best aspects of coco coir are far more varied! Did you know that coco coir possesses antifungal and root promoting properties? As coconuts spend long periods of time floating in the sea before they beach themselves and sprout a lovely new coconut tree, their physical dynamics have to be incredibly tough and unique to survive such a harsh, salty environment and still be able to sprout and grow when the time arises. These properties are available for you, the indoor gardening aficionado, to freely exploit in your quest for your perfect indoor garden. Recent studies have shown that coco coir has a great ability to suppress and protect plants from phythium and phytophthora, two very unpleasant root diseases that can quickly ruin your crop and put a real dampener on your day, week or month! This is very helpful if you are using organic-based nutrients, as these can contain high levels of urea that can build up and burn your plants.

Qualities of Coco Coir

• Coco has ideal pH in the range of 6-6.7
• It holds 8 to 9 times its weight in water
• It holds 22% air even when fully saturated!
• It has excellent drainage and air porosity for better plant growth
• The top layer always remains dry, leaving behind no chances of fungal growth
• It never shrinks, cracks or produces crust
• It aids in suppressing fungus gnats, to a degree
• Excellent cation exchange
• Its anti-fungal properties help plants to get rid of soil borne diseases (inhibits pathogens like phythium and phytophthora)
• Extremely easy to re-hydrate after being dehydrated
• It is a 100% renewable resource
• Lightweight
• Completely environmentally friendly

So what makes good quality coir?

There are three parts to a good coco medium: coco fiber, coco pith (coco peat), and chips. Each part brings its own attributes to the table.

Coco Pith

Coco pith / coco peat holds a large amount of water but is smaller and facilitates much less capacity to hold air. It is more lignin (woody) and decomposes very slowly. Properly aged, it contains the complex that holds potassium and sodium until it is fertilized and a stronger ion, usually calcium, bumps these off, thereby locking up the calcium and freeing large amounts of harmful salts. Proper aging of this coco pith is critical. It affects the crop time since a minimum amount of time is required to make this usable, at least four months, which reduces the amount of time available for use.

Coco Fiber

Fiber holds little water but increases the capacity to hold air; the more fiber you see in your coco mix, the more often you will need to water it. Fiber is largely cellulose and degrades fairly quickly. This degradation has an adverse affect on the stability of the medium. The length of these fibers is also critical to these functions as well.

Coco Chips

Coco chips combine the properties of the fiber and pith; they are approximately the same size as the fiber and positively influence air-holding properties while holding water. Chips hold less water than pith or fibers. They have the highest air to water ratio of all three parts. Achieving the correct ratio of these components is critical in developing a well-drained, well structured medium for growth, just as the proper preparation of the chemical characteristics is important by buffering the blend before use. (Hydroponic-grade coco coir growing medium has been treated so that unwanted potassium and sodium has been removed. This helps to ensure that the nutrients you later add to the coco coir can actually be used by your plants.)

Storage and Sterilization

Coco is usually stored in giant piles for a couple of years at its country of origin. Unless stored carefully, these huge coco piles can be susceptible to colonization by unwanted pathogens (partly due to the pH of the coco being favorable to pathogens) so, in this case, the coco must be steam or chemically sterilized in order to make it suitable for horticultural use. However, chemical sterilization can have adverse effects; and steaming destroys the structure of the coco peat while converting any nitrogen present into a toxic form, nitrite nitrogen; both destroy any beneficial organisms that are usually present. So what’s the solution? A coco coir supplier needs to control the coconut from harvest to bagging, remove the opportunities for unwanted seed and pathogen contamination, and carefully control the aging process directly. Only then will they stand a chance of producing the cleanest, most alive and most productive form of coco coir. Regulations vary between countries with regard to sterilization (Australia is very strict). Shipping microbes across continents is frowned upon by customs agencies. Some brands are inoculated with specific microbes that are either allowed to cross borders or are blended after landing on the shores where they ultimately will be used.

Finally, caring for the product through proper storage and packaging is critical, after preparation and again after packaging. Storing it too wet speeds decomposition. Drying in big mechanical driers can also have a detrimental effect on structure. In short, improper handling will drastically reduce the ability of the product to provide the correct root environment for proper root growth. Finally, consistency: a grower needs to be sure that they are growing in the same material crop after crop to ensure success. Imagine the heartache of losing a crop because the salts were not properly washed off your latest batch, or the coco peat is too decomposed – this REALLY happens!

So don’t be afraid to ask questions of your coco supplier. Look for an established supplier that sun dries the coco, one that incorporates the correct coco pith, coco fiber and coco chip fractions to get the best blend. This is specific to the grower’s irrigation system, the plants being grown, and the size of the pots used. For instance, you wouldn’t grow orchids in fine coco pith as they require lot of air! Conversely, any fast growing vegetable in warm conditions would enjoy lots of coco pith in the mix. Look for coco that is clean and washed correctly, one that is packaged and stored correctly, and one that is correctly aged.

Preparation

Let’s take a look at how this natural product should be prepared by the manufacturer. This is the biggest concern in selecting coco coir for hydroponics use. The outer fibers of the coconut are removed by soaking them in water. This soaking process involves either the use of fresh water or, more commonly, the use of tidal water which can be very high in salt. As coco coir has an excellent cation exchange ability it tends to hold onto things like salt which, when used in a hydroponic or indoor set up, can wreak havoc on your plants. Good quality, hydroponic grade coco coir will have not have a high salt content, but you should always flush it through with a low EC nutrient solution before use until no more tannins are coming out. Tannins can easily be seen as they stain or color the water brown. Some indoor gardeners check to see if the PPM of the water coming out of the coco is the same as the water they’re putting in – but a more reliable method is the 1:1.5 extraction method which better determines the actual pH and EC of the coco itself.

The 1:1.5 Extraction Method

A reliable method for measuring the nutrient levels in coco coir is using the 1: 1.5 extraction method. EC and pH of the root environment can be determined by using this method. The pH and EC of the drain water generally deviates from the actual root situation, as coco coir is able to retain and release elements.

1) Take a sample of coco. This can be done with a soil core sampler or a trowel. To get a representative sample the coco must be collected from as many places as possible.
2) Collect the sample in a bowl and determine whether it contains the right amount of moisture. The coco has the right amount of moisture if moisture disappears between your fingers when you squeeze it. Add de-mineralized water if necessary and mix the coco.
3) Take a ½ pint (250 ml) measuring jug and fill it with just over 4 fluid ounces (150 ml) of de-mineralized water. Add coco to the ½ pint (250 ml) mark.
3). Fully mix and allow the slurry to settle for at least two hours.
4) Mix again and measure the pH.
5) Filter this material out and measure the EC of the water remaining.

The target values for EC are between 1.1 and 1.3 (of course, lower is acceptable too!).
Target values for pH are between 5.3 and 6.2.

Reproduced with permission. Copyright CANNA.

The best way to irrigate coco coir in pots is via drippers. This is the best way to ensure that the growth media remains consistently moist (but not overly wet).

Coco-specific Nutrients

There are a number of manufacturers out there who offer a ‘coco specific’ nutrient formula. These specific formulations are based on the tendency of coco coir to hold onto phosphorus, while only holding a little calcium, while giving off small amounts of potassium. The best nutrient formulations for coco coir will therefore have some extra calcium, but not too much as it will compete for potassium uptake resulting in a potential for potassium deficiency. So are they any better? Well, generally speaking any good, complete hydroponic nutrient is more than suitable for coco coir as these invariably contain all the calcium needed to provide for excellent growth in coco coir. However, for best results, a purpose-made nutrient is best. When feeding nutrients to plants grown in coco coir, aim for a pH of around 6.0 as this will allow maximum availability of all nutrient elements. Remember, a slightly fluctuating pH is a good thing (say between 5.5 and 6.5) as it opens the doors to different nutrients. As for feeding times and frequency, that is really going to depend on what type of system you are running; but for those replacing their peat mix or rockwool with coir there is essentially nothing you need do differently, as far as feeding frequency, flushing, et cetera goes.

So there we have it. Coco coir is an amazing and renewable medium that is ‘top class’ for both performance and benefits. So go on and try this amazing medium, you’ll be glad you did.

CONTRIBUTORS:
Geary Coogler, B. Sci. Horticulture, HORTISOL North American Research
Adam Hanscom, General Hydroponics

General hygiene

Together with disinfection of the nutrient solution, the importance of the above-mentioned aspects of hydroponic practice is usually grossly underestimated and, without due emphasis, good and consistent results will not be achieved. I guess downplaying the need for hygiene is an intuitive logic thing which is based on the rationale that because plants grow in dirt, dirt is OK!!

Absolute cleanliness of the growing area is a must to achieve maximum growth and minimum problems from pests and diseases. Thus, diseased foliage should be promptly removed from plants and, along with general debris, removed from the growing area, with surfaces kept clean from dust, dirt and spillages (Fig 11.1). Minimizing personnel traffic in the area, no smoking, and filtering the air supply to the area are other very worthwhile precautions (Fig 11.2).

Nutrient disinfection

It’s common to hear gardeners blaming their nutrient for poor growth results. However, in many cases, the true cause is the failure to regularly disinfect the nutrient solution.

Unlike soil culture, hydroponic nutrient solutions are exposed to the atmosphere and are therefore a perfect breeding ground for many types of disease (e.g. pythium, fusarium). To prevent disease ingress, the nutrient solution, medium, roots (etc.) should be regularly sterilized (Fig. 11.3).

‘Sterilizing agents’ must yield a residual chemical when dissolved in the working nutrient so that the entire system is treated each time plants are watered. Historically, chlorine dioxide, sodium hypochlorite and monochloramine are used for this purpose.  However, monochloramine has the advantage of possessing a long half-life, is gentle on roots, and is compatible with most of the ‘organic’ mediums and growth promoters used in hydroponics.

Replacing Nutrients

In recirculating hydroponic systems, the nutrient solution must be regularly replaced. That is, it should be completely drained and replaced with fresh nutrients.  This is done to maintain the nutrient’s balance and prevent the build-up of nuisance and harmful salts (e.g. sodium, chloride), pathogen, dirt, etc.

In both winter and summer, generally dump at least every 2 weeks. The dumping frequency can be less if using rain or RO (reverse osmosis) water.

Salty water: More frequent dumping (e.g. every 7 days) may be necessary when using salty make-up water because nuisance chemicals build up more rapidly to toxic / precipitation levels – especially during hot, dry weather.

Method of dumping: Poorly designed hardware can make dumping a tedious and messy task such that there is a temptation to delay or perform less frequently than necessary. So consider this at the design stage – or before you buy. Unfortunately, most system designs are not sympathetic to the hassles of dumping. Consider the advantages of the following design features:

1.  Install an in-line 2-way valve between the pump and feed outlets to divert the nutrient flow to waste (Fig 6.1a).

2.  Ideally, design a sloping floor into the tank which drains towards a sump from which the nutrient is drained (Fig 6.1b). This will help remove the last few liters containing the bulk of the sediment. Another simpler method can be to tilt the tank towards the outlet.

3.  ‘Sump’ pumps are convenient for draining tanks (Fig 6.1c). They are light, portable and easy to prime; however, they will typically only drain to a depth of around 1 inch. Hence, a sloping tank floor or built-in sump is needed for best results.

Where to dump: Utilize the remaining nutritional benefit by placing it on your garden or applying over a large area of grassland, etc.  Do NOT put down drains, toilets or in waterways or pour into sand as this can cause environmental damage (e.g. algae bloom).

Flushing of root zone with fresh water

Hydroponic systems must be regularly flushed and cleaned with fresh water. (Also, note that for disease control, external hardware cleanliness is as important as the inside of tanks / channels.) This is done to remove the build-up of too much calcium (white precipitates – causing blockages) and unwanted / harmful salts (e.g. sodium, chloride), root exudates, algae, pathogens, etc. from the root zone, medium and other system parts.

Pay particular attention to flushing of the root zone and feed circuit. Further, inspect filters, inlets, and outlets, etc. prior to replenishing the system with fresh nutrient because they are prone to becoming blocked with solid material dislodged during the flushing process.

Re-circulating systems: Flushing is done immediately following each dump cycle. Firstly, do any necessary manual cleaning, i.e. remove any obvious build-up, etc.  Partly fill the reservoir with fresh water, then operate the pump with the aim of flushing the feed circuit and root zone / medium (flushing can be enhanced by spraying with a garden hose). Discard waste using the methods advised for dumping. Repeat process until waste water is clear and conductivity is close to that of the make up water.

Run-to-waste systems: Although it is relatively common for many hobbyists to flush only every 7-14 days, some commercial growers consider it necessary to flush daily! The frequency ultimately depends on salinity, temperature, medium, plant variety, and other factors.

Flushing methods are:

a) If flushing can be scheduled to occur when the working nutrient tank is empty (i.e. between nutrient batches), then the existing system hardware can be utilized. Place low alkalinity* water in the reservoir and operate the nutrient pump until the EC of the run-off water is significantly lower than the normal operating EC or no higher than ~0.5mS above that of the water in the reservoir. Where the surface of the medium is readily accessible, it can be beneficial to do additional flushing with a garden hose.

* Lower the pH of tap water to ~5.0.  RO or rain water will not need adjusting.

b) If flushing needs to be conducted more regularly than in the scenario above, then the same procedure applies. However, it will be necessary to have a dedicated reservoir and pump for flushing (Fig 6.3). This can be connected to the existing feed circuit at a junction controlled by a 2-way valve. This valve is simply diverted to this reservoir to apply flushing whenever flushing occurs.

Post harvest clean-up

Two separate procedures are required to ensure hardware is clean prior to replanting:

Disease Prevention

At the end of each crop, it is necessary to sterilize the entire hydroponic system to help prevent disease problems in the next crop. The following guide will help remove organic build-up from pathogen, algae, slimes, and dead/decaying plant matter (Fig 11.4):

Step 1. Remove all plants and media, then do as much manual cleaning as possible. External cleanliness is as important as internal.

Step 2. Partly fill system with water. Lower the water’s pH to below 5, then, with subdued light conditions, add household chlorine bleach** (50g/L chlorine) at ~5ml per liter (4 tsp per gallon).

Step 3. Mix well, then soak system for 24-72 hours. (Note that chlorine bleach will not dissolve algae or general solid material. Only wet brushing will remove those contaminants.) Suitable treatment over that time includes:
-  For re-circulating systems, run the pump for at least 15 minutes every hour.
-  For run-to-waste systems, run the pump for a short burst once every hour.

Step 4. Afterwards, discard this solution, then flush the whole system several times with small volumes of fresh water to remove all traces of chlorine, dislodged material, etc.

Step 5. Where fine drippers, sprayers, and so on are used, it may be necessary to individually dismantle and clean each unit.

Precipitate Removal

Over the long-term, it is sometimes useful to conduct an acid** flush to help remove precipitates (white precipitates of calcium sulfate and phosphate – see Fig 11.4b) that cannot be dissolved with plain water or wet brushing.

Step 1. Firstly, treat the system as detailed for “disease prevention” above.

Step 2. To tank, add water and enough hydrochloric acid to achieve pH 2. For example: if using rain or RO water, dilute 30% (i.e. normal commercial strength) by around one thousand fold, or 1 ml per liter (3/4 tsp per gallon).

Step 3. Soak system for 24-72 hours. Suitable methods might include:
-  For re-circulating systems, run the pump for at least 15 minutes every hour.
-  For run-to-waste systems, run the pump for a short burst once every hour and collect the discharge.

Step 4. Afterwards, neutralize solution up to pH 5-6 with soda ash before discarding.

Step 5. Flush the whole system several times with fresh water to remove all traces of acid, dislodged material, etc.

Step 6. Where fine drippers, sprayers, and so on are used, it may be necessary to individually dismantle and clean each unit.

** Be sure to follow necessary safety precautions and contact no metal parts.

UGM would like to issue a huge thank you to Bob Taylor and his colleagues at Flairform (www.flairform.com) for allowing us to publish this article.