How Long Does It Take to Flush a DWC System?

This post contains affiliate links. As an Amazon Associate earns from qualifying purchases.

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 UsedAverage Flush Time
Soil-based2-3 Weeks
Coco Coir <1 week
Rock Wool 3-4 days
Aeroponics2-3 days
DWC Hydroponics 2-3 days

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.

Flushing helps to rid the plant and root system of excess slats, minerals and nutrients

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.

Flushing can improve the flavour profile of your crop if completed close to 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.

Related articles


William, an experienced consultant and passionate advocate for technology and sustainability, is the founder of Smarter Home Gardens. William's journey into gardening began with the purchase of his first home, which came with a small backyard garden. Despite initial challenges brought about by limited space, soil, and sunlight, William's determination to create a vibrant garden led him to research and experiment with innovative gardening technologies and sustainable practices. Driven by his lifelong enthusiasm for technology and sustainability, William explored various gardening methods, including vertical gardening, hydroponics, companion gardening, and composting. Through these efforts, he realized that it was possible to combine his passions with his newfound love for gardening. Smarter Home Gardens was born out of William's desire to share his research and experiences with others, helping them create smarter gardens that leverage cutting-edge technology and contribute to a more nature-positive world. The blog offers in-depth articles on innovative gardening technologies and methods, helpful 'how-to' guides, reviews of the latest gardening technology, and research on cost-effective garden maintenance solutions. William's commitment to sustainable and technologically-driven gardening has made him a trusted voice in the field. His enthusiasm for creating gardens that work with the planet, rather than against it, is evident in every post he shares on Smarter Home Gardens. Through the blog, William hopes to engage with a wider audience, encouraging others to join him on this exciting journey towards smarter, more sustainable gardens.

Recent Posts