Hey You – Get out of the Dirt!
By Erik Biksa
From region to region, different growing mediums have different levels of popularity. Some of this is based on the availability of a particular substrate, but more often than not different areas have different growing methods. Some of this variability can be attributed to the preferences of local strains and the experiences of local veteran growers. On an individual basis the choice of growing medium is often based on: the type of system, the skill level of the grower, time availability for crop management, environmental conditions, costs, and the scale of the crop. It would not be accurate to say that there is one best growing medium for all growing situations. It is the intention of this article to highlight some areas in the “hydro” VS “dirt” debate.
Firstly, the term “dirt” typically refers to soilless mix. Soilless mixes can be made up from an endless array of ingredients; however, more often than not they are an amended peat mix. Recently, coconut coir has gained some popularity for North American indoor growers, while it has been popular overseas for some time now. Peat based soilless mixes have been used throughout the nursery trade for decades.
With regards to indoor growing, there has been a shift towards growing in peat based soilless mediums. Part of the reason for this shift is the increasing number of new growers who are looking to ensure a successful crop, given their limited amount of experience. Some experienced growers have made the switch as a result of keeping up with the latest trends, or for the sake of convenience. Large commercial growers typically aren’t concerned with maximizing yields on a square foot basis, so the lesser yield is offset by the convenience of “dirt”. However, if you do the numbers an extra 10-15% yield per square foot over several hundred square feet should start to get some people thinking. Often, less experienced retail staff are eager to suggest a soilless mix to grower, as there is much less explaining to do and there is a reduced chance of a customer returning to the shop angry as the result of poor advice or instructions. Lets face it, how complicated is dumping the contents of a bale of soilless mix into containers? This may seem like the natural choice, especially when growing larger plants, as recent trends dictate. However, if you want to reap maximum yields at harvest you will be forced to look further. This is not to say to discontinue using peat mix, but open your eyes to specialized management techniques, some of which include intensive hydroponic plant production. Some growers may have debate with the following statement, but I will stand by it: You can harvest more, quicker, in a fine tuned hydroponic system than you can in “dirt” based systems. The statement is based on many years of intimate experience with many types of growing mediums and cropping techniques, research, and discussions with other veteran growers.
Also note that if you intend to regenerate crops, plants grown in water based systems not confined to containers may never become root bound. Bare roots may also be pruned for regenerative crops, as is often done by commercial rose growers. When asked why they grow in “dirt” most growers respond:
- It’s easier
- More flavor
- Greater dry matter
- That’s what my friend taught me
Yes, dirt systems are easier to set-up, but are you really saving any time? First, consider actually picking up your growing medium. Large bales of soilless mix are not much fun to transport, especially from your driveway into the house, and down flights of stairs. Have you ever had a bale with a hole in it leave a trail from the front door to the basement stairs over your nice, new, white carpet? We haven’t even gotten into the time and mess of mixing in specialty additions. What about disposal? A truckload of root balls is about as much fun as hemorrhoids. In some hydroponic systems only one or two liters of sterile, dirt free growing medium are required for weighty four inch plants. A simple to use and operate bucket system using six inch net pots and lecca pellets is an excellent example. After all, in hydroponics the growing medium needs only to help support the plant as the magic is in the nutrient solution.
Plants grown hydroponically are able to make much more efficient use of fertilizers, as nutrients tend to be more available. If you notice a deficiency (very rare) in a hydroponic system and correct it, you will see an improvement within a couple of days or sometimes, even hours. In soilless mix, if you notice a deficiency (fairly common) it can take weeks to notice a change after adjustments, if a change is going to occur at all.
The same can be said for controlling pH levels in the root zone. The pH level at the roots has a tremendous influence on the availability of nutrients. Some nutrients will become more available than others throughout a range of pH levels. In a hydroponic system, simply adjust the pH in the reservoir with an acid or base and the pH at the root zone will be adjusted instantaneously in a recirculating system. It is also much easier to get an accurate reading of the pH of a nutrient solution than it is for a soilless medium. Remember that in a water based recirculating system, the nutrient solution becomes the growing medium. In peat mixes, growers carefully adjust the pH of the nutrient solution, but rarely know what the actual pH is in the root zone. Many growers are often shocked to find that their roots are sitting in a strongly acid soil by the time harvest approaches. This may occur due to the fact that the chemistry in the root zone is a result of the accumulation of compounds supplied by the grower and created by the plant, which can build up to reach detrimental levels.
Some might say that the answer is simple: leach the soil. Yes, this will help to remove some accumulated elements from the root zone, but it will also wash valuable nutrients taken up and stored by the plant. This occurrence is reverse osmosis. As a general rule of thumb if a membrane (root) separates a mild solution (leaching water) from a concentrated solution (nutrients stored in plant) the stronger solution will travel to the weaker solution until equal concentrations are created.
In recirculating hydroponic systems and especially water based systems, salt build up occurs less frequently, reducing the amount of leaching required (if at all). If leaching is required, nutrients washed out of the plant can quickly be replaced as nutrient uptake occurs quickly because of the high degree of control in the root zone. The leeching process is also much quicker in a hydroponic system. Simply run pH adjusted plain water or one quarter strength nutrient solution for a few hours and resume your regular feed program. It might take several days of leeching to achieve the same effect in “dirt” systems.
On the subject of leaching, growers who use soilless mix tend to feed the plants only pure water up to one to two weeks prior to harvest to reduce any harshness in the finished product. Phosphorous is required in significant quantities for profuse blooms and is easily washed away from the medium and to some extent the plant tissue. In stripping this valuable element away from the plant, you are not only removing an element required for increasing mass, but you are also removing an element aiding the preservation of the active compounds produced by the plants.
For irrigation, either soilless mix or hydroponics can be automated with a pump and timer. The biggest difference is that in hydroponic systems, nutrient delivery can saturate the root zone with plant available oxygen. To a degree, in water based systems, more irrigation means more oxygen at the roots. In soilless mediums, over applications can mean disaster due to root rot and other potential problems. Fungus gnats, which can infect plants thrive in over watered peat mixes along with other pests such as harmful bacteria associated with blights. These types of conditions have been described as “bog-o-ponics”. Larger volumes of nutrient solution or chillers can also help to cool the root zone in hydroponic systems. In doing so, the upper green portions of the plant will continue to flourish in warmer than optimal conditions. In nature, the soil is always cooler than the air. However, containers heat up quickly, bringing root zone temperatures to dangerous levels. A digital min/max thermometer with a probe can tell you just how warm the root zone is getting in either hydro or dirt.
Soilless mixes can be reused, but a fresh medium to help prevent disease and provide optimum nutrition is recommended. Soilless mixes can be leached heavily and should be sterilized. Chemical sterilization is hazardous and steam sterilization is time consuming and energy intensive. In an Aeroponic system, simply scoop out the root mat and rinse with a mild bleach solution. You can have a new crop planted hours after you harvest, and with peace of mind.
Some of the above points may make re-circulating systems sound enticing, but they do require more attention to detail. The nutrient solution level must be kept topped up to ensure optimal uptake. A float valve supplying fresh water or one quarter strength nutrient solution is easy and inexpensive to install. It can also mean fewer trips to the grow room. The larger your reservoir, the more stable your nutrient solution becomes with regards to pH fluctuation and increasing TDS levels. Very large reservoirs may need to be completely replaced only once or twice through the vegetative stage. During flowering, it is wise to change and adjust the nutrient solution more frequently in order to keep up with the plant’s changing nutritional demands.
As for flavor, organically grown crops due often taste a little better but tend to yield a little less. You can add organic supplements in later stages of hydroponic production to bring nature to technology. Bioponically grown crops are grown in hydroponic systems or mediums but are fed a balanced diet of organic nutrient teas which have been carefully filtered to prevent clogging of emitters, etc. As a rule, and contrary to “dirt” crops higher TDS levels (i.e. 1500ppm) towards harvest in hydroponic systems can greatly help to improve the flavor of crops such as tomatoes. Take care that in raising your TDS you are not overdosing with nitrogen, which can occur more readily when using a one part solution. Commercial tomato growers will sometimes use sodium chloride (NaCl-) in place of potassium (K+) to raise the TDS/EC in order to improve flavor and bolster sugar levels. Plant available sugars and carbohydrates added to hydroponic systems can do wonders for taste and often yields.
With proper irrigation management hydroponic crops can have equal or greater dry matter values when compared to crops grown in soilless mediums. This “management” can be as simple as installing a flow control valve in the delivery line. Maintain you current timer settings, just cut back on the amount of moisture being delivered with each irrigation. This practice is especially applicable to easy to operate flood and drain systems. In intermittent Aeroponic systems, set the timer to cycle less frequently towards harvest, but take care not to allow the root zone to overheat or become stagnant. In re-circulating systems such as bucket systems, simply lower the level of the nutrient solution in the buckets. The additional air space will help you achieve a greater percentage of dry matter in your crop. This will mean that you will have to change the solution a little more frequently, even with a float valve. However, more frequent nutrient solution changes towards harvest often result in higher yields and better quality.
Growers want to see growing technology to continue to move forward, and it seems that growing in dirt is taking a step backwards. I would never dissuade somebody from continuing a practice that gives him or her results, but I would like to encourage growers to experiment. If you have been successful in soilless mediums, try growing in an inexpensive bucket system, even if on a limited trial scale. You may find that you can spend less time to achieve the same mass, so you can flower earlier. If you have grown hydroponically with success in the past, take a stab at growing aero-ponically. With proper management, these systems can be more productive than you could have ever imagined possible. Always feel free to contact Maximum Yield along the way.