In the first and second installment of this series, Lawrence Brooke, founder of General Hydroponics, took us through how to maintain a healthy growing environment and some methods of dealing with plant sickness.  In this third and final part we look at how to introduce beneficial biologicals into a hydroponic growing system.

Biofilters

Think of beneficial biologicals and you probably imagine them in an organic / soil environment.  However, it’s also perfectly feasible to introduce them into a hydroponic growing environment using a Biofilter.  These devices are available at any aquarium / fish supply store (and some grow stores) and can assist in the maintenance of colonies of beneficial microorganisms for hydroponic systems.  Biofilters can also help to keep your nutrient solution cleaner and more aerated.  The very high surface area, combined with constant flow that aerates the solution 24 / 7 – this, in turn, creates an ideal environment for the beneficial organisms while removing discarded compounds that plant roots exude.

It is, of course, essential to provide an inoculation of beneficials to create the population in the first place; the Biofilter gives them a base-camp to operate from.

It’s very important to use products that are designed to operate in a hydroponic nutrient solution.  Your first job is to establish mychorizzae colonies on the roots.  A week or so later, add colonies of beneficial bacteria. Don’t go the other way or the bacteria will dominate the mychorizzae. Once a population is established very little needs to be added later, just a small amount each week or with nutrient changes, or after treating the plants with a ‘shield’ or neem product that has been applied as a drench. Nb. The drench method involves inoculating each plant individually using a watering can.  It is easy, effective and more economical than adding products directly to the reservoir where huge amounts of water can require larger doses.

In effect the biofilter draws in from your nutrient stream, then with its own built in pump circulates the nutrient across a matrix of high-surface area media. They are sized according to the reservoir size.

So if you’re one of the many growers who want to try using organic nutrients in a hydroponic system, make sure you invest in a biofilter!  For regular hydroponic use with purified soluble mineral based nutrients, an additional benefit is that you can usually get equal or better growing results with milder nutrient, save some money and reduce environmental stress from discarded nutrient.  Exponents of this method believe that this mixture of living nutrients but with purified soluble minerals leads to better tasting produce.  If you want to experiment, my best advice is to mix your nutrient solution using a high-quality hydroponic nutrient product, making it milder by about one third, and keep your biofilter running 24/7.

Who’s for a Brew?

Another powerful tool is the addition of ‘tea’ containing beneficials to the nutrient stream, and in some cases for foliar spray, irrigation, for germination and cuttings.  This isn’t the sort of tea Brits have with cake in the middle of the afternoon.  We’re talking about high quality ‘compost tea’.

Compost tea should be looked at as a process, not a product.  There is a broad range of systems and inoculants that are promoted as being good for plants.  The key to producing excellent compost tea is extreme aeration since the high oxygen in the solution will favor beneficials and challenge most disease organisms.  Typically both good and bad organisms are in the starting inoculant, usually Compost or ‘Forest Litter’.  “Alaska Humus” is popular and proven as an excellent starter for compost tea. It contains the huge spectrum of organisms that have evolved in arctic forests for thousands of years. Alaska Humus is basically forest top-soil.  The bio-diversity is enormous and generally favors beneficials.  The use of forest litter for making tea brings in beneficial fungi, bacteria and other symbiotic organisms; generally a much larger diversity than compost alone can provide. If you use compost then the quality of the tea will be directly related to the quality of the compost…. Good compost = good tea, nasty slimy compost = trouble. For more information read ‘Teaming with Microbes’ by Jeff Lowenfels, published by Timber Press.

For those growers who prefer ‘Organic’ products and methods, compost tea is the embodiment of the organic method.  It’s not just natural, it’s alive and vibrant.  The natural forests of the world grow without external inputs of fertilizer because the beneficial microorganisms in soil, air and water are the tenders of plants and forests, feeding and protecting plants growing in the natural environment.

Water and Nutrient Quality

As I mentioned last time, good water is a great advantage, poor water is a real challenge for growers.  If you want to grow plants hydroponically, use only the highest quality plant food, designed specifically for hydroponics. Low grade plant foods and common fertilizers offer your plants poor and incomplete nutrition, cause pH drift, and sometimes contain impurities that can become toxic to hydroponic plants, particularly in the root zone… think of common garden fertilizers as ‘junk-food’ for plants; this includes all of the garden fertilizers sold at big-box stores. They are formulated with cheap, impure ingredients and totally incomplete and out of balance. If the primary ingredients are ‘Urea and  Ammonium Phosphate, with no Calcium or Magnesium … then they are designed to give your garden plants a quick ‘fix’ while slowly poisoning your soil. Only high-quality plant food can grow superior plants. Healthy plants grow faster, generate higher yields and are resistant to disease and insect infestation; they are better tasting and yields are much higher.

Are You Taking Notes?

Keep notes on your observations of make-up water EC, EC drift, pH drift, total water usage, temperature range, both nutrient and air and comments on crop health and progress.  When you mix fresh nutrient always measure carefully.  Keep an eye on pH and an especially close watch on nutrient strength (PPM, EC, dissolved solids). Look out for diseases and remove and destroy sick plants immediately. As a rule of thumb 1,000 ppm translates to .5 miliSiemen so you can interpret ppm from an EC meter, or EC from a ppm meter.  They are essentially the same meter, just different ways of expressing the information or conductivity / nutrient solution strength.

Control your nutrient temperature – use a heat mat under your reservoir or high quality aquarium heaters to warm nutrient in the winter and look for chillers to cool your nutrient in the summer if high nutrient temperature becomes an issue.  Remember, above 72°F (22°C) the oxygen content in a nutrient solution can drop quickly. Locate the reservoir remotely in a cooler room or underground for greenhouse cultivation if your environment lends itself.

Generally if you are growing in a hot and dry environment, and the plants are big and growing fast, it is usually best to run milder nutrient.  This is in part because the higher transpiration rate will increase EC in the nutrient. If it goes too high it can become toxic to the crop.  It is better to be too mild than too strong.  If you want to run stronger nutrient, then you need pure water, more light, airflow, cool temperatures and robust plants.  Extra C02 in the air-supply can pay off here, particularly for young plants during early vigorous growth.

As a last word, please don’t be overwhelmed or intimidated by all this information. Plants can tolerate quite a lot of stress and still produce well. On the other hand the grower who knows the questions and how to find answers is the one who will have consistently good crops. It is far easier to avoid problems through knowledge and proper technique than to fix them after they arise.

Happy growing!