Recirculation or Residual Water Disposal?

There are dozens of different cannabis growing principles, hundreds of unique techniques and perhaps thousands of different growing systems. Each is designed with the intention of solving a problem, making life easier or simply giving you more value for money. When it comes to watering your plants, all existing combinations and variations can be reduced to two principles. Each has its advantages and disadvantages. And what is an advantage for one grower may prove to be a disadvantage for another, depending on the circumstances. There are only two ways to water your plants. Either you use a recirculating system, or an approach based on draining residual water.


Simply put, residual water runoff occurs when you water your plants to a point where a recommended 15-20% by volume begins to drain from the growing medium. This runoff water is completely drained away. In a recirculating environment, the excess water is collected and used to feed other plants. It seems pretty simple, but let’s not forget that plants absorb nutrients when they are fed and also excrete unwanted minerals and organic matter. There are several advantages and disadvantages to both methods. Only your experience and style will determine which is best. Talk to any experienced growers and you are sure to hear about the many different systems and methods they have experimented with. Recirculating feed is not synonymous with hydroponics. Likewise, disposing of wastewater is not necessarily organic. In fact, an aquaponic system is the epitome of an organic, recirculating hydroponic system. Some of the most crop-intensive, technologically advanced hydroponic growing operations today run solely on residual water runoff. Think fast-growing vegetables, microgreens or intensive livestock feed production. The most important factors to consider with each of the methods are the growing environment and how well the plant species is able to handle the advantages and disadvantages.


The best way to answer this question is to turn to Mother Nature. Have you ever seen a pond with no flow of water, but full of life? If so, that is technically a natural recirculating setup. There is no best option. There are only different methods that fit the needs of the variety, the location, and the objective and ability of the grower. Cannabis is a wondrous plant. One of its wonders is that it can quickly adapt to extreme environments and conditions. It is quite resistant to both drought and waterlogging and resilient to insects and pathogens. This makes weed the perfect candidate for whatever watering system is in place.


The traditional way is to dispose of residual water. This is what most people imagine when they talk about watering plants or farming. But it also has a place in high-tech greenhouse farming. You water your plants until the excess water comes out, which guarantees that your soil is fully soaked, providing even nutrition to the roots. The nutrient solution is freshly prepared before it is applied. And when using chemical fertilizers, draining residual water ensures that there is no salt build-up in the medium. Each watering serves as a kind of small-scale flush. In this technique, the nutrients are fresh and the water is oxygenated. You can easily use organic fertilizers. After all, you generally don’t prepare a nutrient tank where they would sit still for a week or two. It is possible to prepare nutrients for all your plants, or if necessary, adjust the NPK ratio and micronutrient profile to individual plants. Whether you do it as an experiment or for deficit recovery. In recirculating systems, you cannot use organic nutrients for growing weed. That’s simply the recipe for disaster. Theoretically it is possible, but it is a pathogenic nightmare. Unfortunately, an aquaponic system does not perform adequately to thicken the buds. In recirculating systems, prepare one nutrient solution for the entire crop in a reservoir. The larger water volume ensures a more stable pH and chemical composition. This allows you to supply a large number of plants simultaneously. You save 15-20% in water and nutrient costs if everything goes smoothly. These systems usually require much less labor intensive, daily maintenance. In fact, are there no signs of problems and is the reservoir stable? Then the operation can actually run automatically with minimal maintenance.


When draining residual water, you either feed by hand or use an automated feeding system. In the latter case, you are limited in the number of plants you can grow with one reservoir. The reason for this is that each plant requires its own nutrient and, as the nutrients have to travel a longer distance, efficiency decreases. As a result, you may have to deal with uneven watering. This means 15-20% extra costs if the yields do not outweigh them. In certain regions it is illegal to discharge water containing fertilizers into the sewer system. This requires a special water treatment unit or a waste treatment contract. When using organic nutrients, thorough daily checks should be made to ensure that there are no blockages in the pipes. Just a few accumulations can be a serious problem. With recirculating nutrition, you are not able to tailor the nutrition for a specific plant; the only solution to this is to separate the plant from the rest. Another big risk is that if one plant gets sick, the disease will quickly spread to the whole group before the first signs appear. As plants feed, nutrient values become unbalanced, requiring special laboratory equipment and expertise to determine the condition and dose needed for recovery. This dose can be added to restore the NPK ratio and values of micronutrients. In the long run, recirculation is more cost-effective than the 15-20% loss mentioned with the other system. But the investment in laboratory equipment may deter many growers.


Chances are, you’ll be better off disposing of residual water. Recirculating setups require a certain expertise in a number of areas. This, while disposing of wastewater is a perfect teacher. You learn to understand plants and recognize deficiencies, but also how to get optimal nutrient levels for a certain variety and how to grow multiple plants at the same time. Therefore, our advice is: go for the option where you can learn a lot and in the process strive to become a master grower. Have you reached the level where you know a specific variety inside and out, have created a good line of clones and have a culture that runs flawlessly? Then we advise you to take your system to the next level with recirculation.


If you do it right, you can enjoy the extra free time and the additional 15-20% in savings that recirculating watering offers. However, when things go wrong, they go right wrong. In that respect, disposing of residual water is more forgiving. Modern hydroponics has shown that vegetative plants, which often have very short life cycles, perform tremendously well in recirculating systems. The speed of the harvest cycle and the operational ease of recirculation are certainly pluses. Fruit-bearing crops, such as tomatoes and cannabis, also do extremely well in recirculating situations. But the additional savings are initially outweighed by the equipment and personnel required for analysis. The fact is, however, that in the long run (and on paper) recirculation seems to be the best option. Practically speaking, the risks may overshadow the potential benefits. At the same time, growing medium sized cannabis with an RDWC system (recirculating deep water culture) provides an optimal balance of workload, risk and benefit. So to conclude – is it worth it? Only you can answer that question.