Recirculating vs Run-to-Waste Hydroponic Systems

No matter whether you hand water or use a hydroponics system, and no matter what medium you grow in, all methods of plant growing fall into one of 2 basic categories - either recirculating, or run-to waste (RTW).

Recirculating hydroponics

These are systems such as flood and drain or certain dripper systems like Wilma systems which reuse the nutrient solution which is stored in a reservoir. Once the plants have received a feed, the nutrient solution is returned to the reservoir ready to be used again for the next feed.

The recirculating system has a number of advantages:

  • The nutrient solution is reused so the system is very economical on nutrients.
  • It is easy to hit exactly the right nutrient strength. If the nutrient solution is too weak then the e.c. will go down day-by-day. If the solution is too strong then the e.c. will go up day-by-day. The e.c will remain steady when the nutrient strength is just right.
  • Although a weekly change of the nutrient solution is recommended, this is probably less frequent than with a run-to-waste system.

There is really only one disadvantage to using a recirculating system but it can potentially be a big one. Plants uptake and use the different elements in the nutrient solution at different rates. So, when the nutrient solution is returned to the reservoir and mixed back in it will be less balanced than when it was delivered to the plant.

This process of delivering and returning unbalanced nutrient solution happens over and over. As a consequence, as time goes by, the nutrient solution in the reservoir becomes less balanced as well. This can lead to plant deficiencies. Also, waste products released by the plant accumulate in the reservoir which is not a good thing because they end up being repeatedly passed back to the plant. These are the reasons we recommended that the nutrient solution is discarded and replaced at least once a week. Some experienced growers replace their nutrient solution twice a week to ensure deficiencies don't occur.

These systems are rather different. They feed the plants fresh, unused nutrient solution. The run-off out of the bottom of the pots is drained away and discarded immediately, It is not returned back the reservoir to be reused.

Run-to-waste includes hand-watering in pots and saucers and then the run-off in the saucer being discarded, but this can be made more convenient by using easy draining medusa trays.

Run-to-waste has one main advantage. Because fresh, balanced nutrient solution is delivered to the plants at every feed, the plants are much less likely to suffer from deficiencies, and also the plants are not re-fed any of their own waste products.

Unfortunately, as the run-off nutrient solution is never reused (i.e. discarded immediately), rtw systems are much less economical on nutrients.

As with all systems, both need to be well looked after and cleaned; we'd recommend sterilising them with Silver Bullet roots and silver bullet mist to keep pathogens away, and over the Summer, consider a chiller to maintain ideal nutrient solution temperatures and deter harmful pathogens.

If you want to learn more about any of these systems, click here to find our entire systems catalogue.

Happy Growing

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