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It was quite a while since I started flushing my hydroponics systems. I wasn’t originally bought into it. But, now that I regularly flush my system, I find myself totally relying on it for every harvest. But how long each flush lasts can vary depending on a number of factors.
As a general rule, flushing your DWC hydroponics system can be completed within three days. This is because DWC hydroponics uses very little growing medium which only retains small concentrations of salts, minerals and nutrients. Therefore, the flush focuses on the plant itself which can be washed of any excess elements quickly.
In this article, we’ll take a look at flushing. Specifically, flushing DWC hydroponics systems. We’ll explore what flushing is, why it’s beneficial for your plants and when (and how long) you should do it. Let’s jump straight in.
The basics: What exactly is flushing?
Flushing is a method of nutrient management used by some hydroponic growers to prevent the build-up of excess salts, minerals and nutrients that may have accumulated within their plants over time. This accumulation can negatively affect the plant’s flavour. It involves completely draining the nutrient solution from the reservoir and replacing it with clean, PH-balanced water. The new, clean solution is fed through the system (and any plants it contains) for a pre-defined period of time to ‘flush’ out these unwanted elements.
Factors that affect the flush time
There are a few factors that can influence the time it takes to flush a hydroponics system.
1. Grow medium and nutrient retention
The main factor that impacts the length of time needed to flush your system is the ability of the growing medium used to retain the nutrients within the nutrient solution. Different growing mediums have different water retention and drainage rates.
For instance, traditional soil is very good at retaining nutrients and it can take several weeks for these to disappear. By comparison, other artificial growing mediums like rock wool are poor at retaining nutrients. Resultingly, the time it takes to flush nutrients from the system varies depending on the growing medium used, as shown by the below table.
|System / Growing Medium Used
|Average Flush Time
Because DWC hydroponics requires very little growing medium the flush time is among the lowest in hydroponics. This is because you are principally flushing excess nutrients from the plant, and not the growing medium. The flushing process can usually be completed in 2-3 days before harvesting.
2. Water pump capacity/circulation
Another factor which can impact how long each flush can last is the size and capacity of your water pump. If your pump is not powerful enough to pump water quickly throughout the system and the plant’s roots it may take longer to flush out the nutrients. Additionally, how long you run a pump or if you use a timer to regulate the flow of water, will influence the time.
3. Flush frequency
Flushing your hydroponics system regularly, while not necessary, can help to reduce the accumulation of salts, minerals and nutrients within the growing medium and plants. Regular flushing can help to reduce the amount of time it takes for each flush to remove these elements from the system.
Things to consider when flushing your DWC system
1. Use clean water
The entire point of flushing your hydroponics system is to rid the growing medium and plants of excess toxins, nutrients and other elements. Therefore, using water that is as pure and uncontaminated as possible is important to ensure you get the cleanest flush.
2. pH balance
pH balance should be as close to neutral as possible when flushing your hydroponics system. This means that the water’s pH levels should be within the 5.5 to 6.8 range. Anything outside of this range can negatively impact the effectiveness of your flush.
3. System cleanliness
A build-up of algae and other contaminants within the system can negatively influence flushing. Remember how I said you need to use clean water for flushing? Well, these contaminants can turn clean pretty dirty in a short space of time. Therefore, it’s important to try to prevent and remove algae from your hydroponics system before flushing.
Why should you flush your DWC system?
Flushing your DWC system is important because it helps to remove the potentially harmful concentration of salts, minerals and nutrients that can be accumulated within your plants. This accumulation has the potential to negatively impact the flavour of plants. By flushing the plants with fresh, clean water, you can remove these unwanted elements and thus improve the flavour profile of your plants before harvest.
When could you flush your DWC system?
1. Before harvesting
Flushing is designed to remove excess salts, minerals and nutrients from your plant in order to improve its flavour profile. Therefore, as a general rule, you want to start flushing your DWC system just before you plan to harvest your crop. The length of time needed to flush a hydroponics system can vary depending on the nutrient retention rate of the growing medium used (see table above). Therefore it’s important to plan enough time for the flush to be fully complete before harvesting.
2. If the nutrient concentration is too high
Another time you may consider flushing your system is to re-balance or re-start the nutrient solution. For example, if the concentration of nutrients within the nutrient solution is too high your plants may not respond well and you may start to see a little burning on the leaves. To reduce the nutrient concentration, you may choose to flush the system and run clean water for a few days to a week before adding a lower concentration of nutrients back into the reservoir.
3. If your pH balance is off
Getting the pH balance of your nutrient solution right is an important part of hydroponics. If you get it wrong, and your pH is either too acidic or alkaline you may wish to start over and flush the system. Flushing the system allows you to get back to square one with a neutral pH.
Are there any negatives to flushing your DWC hydroponics system?
Unfortunately, as in all things, there is a flip side to flushing your DWC hydroponics system that can actually have negative effects on your plants.
By using just clean water to flush your system you are effectively starving plants of the salts, nutrients and minerals they need to flourish. This can have a negative effect on growth (and even flavour) right before harvest, which isn’t ideal.
The key here is to flush out excess salts, nutrients and minerals while retaining enough to allow your plants to continue to thrive. Fortunately, there are products on the market like FloraKleen Clearing Solution, Flawless Finish and Canna Flush that support the removal of substrate sand excess nutrients without decimating the plant of what it needs to thrive.
Combining these products with clean water has been scientifically proven to result in a more effective flush, helping plants to retain their flavour and resulting in a better harvest.