Recirculating vs. Drain to Waste Systems
by Sunny Datko
What is the Difference Between Recirculating and Drain to Waste Systems?
There are two forms of hydroponic systems – there are re-circulating and drain-to-waste systems. In a recirculating system, the runoff from the nutrient solution is collected, replenished and reapplied to the substrate. In a drain to waste system, the runoff is drained into the ground or routed to a holding reservoir. Many gardeners choose to use the drain to waste system because this method offers more control over the composition of the nutrient solution being applied. In a recirculating system the solution will gradually become unbalanced, unless the solution is tested for each nutrient. A rapidly growing vine crop such as tomato can remove a considerable amount of nutrients in a day. In a “drain to waste” system the grower can increase the feeding time and be confident a balanced solution is reaching the crop.
Why Run a Drain to Waste System?
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Drain to waste requires less maintenance due to the fact that the excess nutrient solution isn’t recycled back into the reservoir, so the pH of the reservoir should not vary. A recirculating system can have large shifts in the pH levels that require periodic checking and adjusting. If the pH is not corrected, various problems may occur, including but not limited to poor nutrient absorption.
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In a recirculating system, pathogens can quickly spread their colonies and infecting other plants in the same reservoir. With drain to waste systems this cannot happen because any water leaving a given plant goes to a drain and not back to the main reservoir. Therefore the spores cannot infect the reservoir.
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Drain to waste systems allow you to flush your garden more easily, allowing you to reset the medium and draw out unwanted nutrients from within the plants themselves. In a recirculating system, flushing will pull the salts out of the medium as well as the plant, draw them into the reservoir, and then keep pumping them back into the plants again and again, until the reservoir is drained and the cycle is repeated a few times. Since you’re trying to leach nutrients from the plants, it makes sense that you don’t want to keep recirculating them into the garden. By using a run to waste configuration, the nutrients are flushed out of the system completely. All salts and excess minerals are drained from the plants and truly flushed away.
What Are The Disadvantages of Drain to Waste Systems?
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The main drawback of a drain to waste pass system is that fertilizer is wasted. In general, about 15% to 20% of the nutrient solution applied is runoff. This is not a large amount given the control over nutrition that is possible. As technology becomes available that allows for the testing and replenishment of individual nutrients, a recirculating system that provides a balanced feed, without the waste, will be possible.
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Advantages |
Disadvantages |
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Recirculating |
-One water supply can feed a larger number of plants -Conserves water and nutrients, therefore it’s less expensive to operate |
-Diseases can spread more easily and rapidly (especially root rot) -Higher pH fluctuations -Nutrient levels can become imbalanced |
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Drain to Waste |
-Nutrients are always fresh -pH levels are more stable -Nutrient levels stay balanced -Lowers spread of disease -Easier to flush out salts |
-Higher water and nutrient consumption (15-20% runoff) -Cannot feed as many plants with the same water supply (will usually have one water supply for 1-6 plants) |
This post is a reprint of product page that originally appeared at San Diego Hydroponics & Organics and was re-posted on Monday, May 14th, 2012 at 7:00 pm on this site. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
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