Hydroponics Flush: How to Flush Hydroponics Plants

growee - Hydroponics Flush: How to Flush Hydroponics Plants

Flushing plants before the end of the growing cycle is a common practice used by cannabis growers and many others alike. It is a crucial part of the hydroponic growing process. 

Some growers argue that neglecting to flush plants can adversely affect the final product’s quality, making it less enjoyable than if a proper flushing technique were used. Other growers are doubting the importance of flushing your plants before harvest.

Flushing hydroponic plants is a topic of discussion within the gardening community. Let’s explore what flushing entails and how it can be implemented at home, keeping in mind that opinions on its necessity and benefits vary.

What is Flush in Hydroponics?

Flushing in hydroponics is the act of removing nutrients from the watering solution, with the aim being to rid the plants of excess nutrients.

This is done by giving the cannabis or other plants plain water, whether reverse osmosis or regular tap water, without any kind of nutrients.

Some growers may also choose to use a special flushing agent instead of plain water, which is specially designed to quickly rid plants of any remaining nutrients, therefore improving the final result.

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Why Growers Flush Their Plants?

Flush Hydroponics Plants

Some growers believe that the main reason for flushing plants is to remove excess nutrients. They argue, why remove the nutrients from the watering solution, the very nutrients essential for the plant’s growth and survival? The rationale, as understood by these growers, is straightforward: it’s to avoid the retention of nutrients, chemicals, and fertilizers in the flower or fruit post-harvest. Without a proper flushing cycle before harvest, excess nutrients might remain in the plant matter.

In the context of cannabis cultivation, for instance, it’s said that not flushing can result in a displeasing taste, described by some as a metallic-chemical flavor that’s difficult to eliminate. Beyond taste, the smoke from non-flushed cannabis is reported to be harsh and acrid, potentially irritating to the throat due to leftover fertilizers and nutrients. It’s believed that even diligent drying and curing can’t fully remove these excesses.

Above all, consuming high amounts of plant fertilizers and nutrients is considered unhealthy by some. Hence, according to these viewpoints, growers choose to flush their plants for these and other reasons, aiming for a cleaner and more enjoyable end product.

During What Part of the Growing Cycle Do Most Growers Flush?

The vast majority of growers flush their plants during the flowering cycle, just before harvest time. This is done right at the end of the flowering cycle, when the plant still contains enough nutrients to survive for a few more days without the grower supplying additional fertilizers.

You might think that this could lead to a nutrient deficiency, but if the timing is right, the plant will be able to use up the excess nutrients by the time the grower harvests, and because the plant is being harvested, it won’t need any more nutrients afterwards.

The key here is timing, as when to flush a cannabis plant depends on the growing medium. For most people who grow in soil, flushing needs take place roughly one week before harvest, as the soil holds onto a lot of nutrients, and it takes quite a few days for plants to use up the rest of those substances.

However, the same is not the case for hydroponics, as there is no soil, which means there is no medium where the nutrients are stored for long periods of time. The water used in a hydroponic solution can’t store nutrients for prolonged release like soil does.

With hydroponics, because the nutrient delivery through water is so immediate, when flushing occurs, the nutrients also stop being supplied to your plant virtually right away. 

Because there is no soil to hold onto some of the nutrients, the levels drop much faster. Hydroponic plants being flushed deplete their stored nutrients very quickly, within just one or two days.

Remember that if you flush your plants too early, they won’t get the nutrients they need in the last leg of their flowering cycle, which can negatively impact both the yield and the quality of the final product.

The Effectiveness of Flushing Hydroponics and Why it is in Debate

Flush Hydroponics Plants

There is however a bit of a debate as to how effective flushing hydroponic plants is, and whether or not it should be done at all. There are those who support flushing hydroponically grown cannabis, whereas others do not.


What Growers That Support Flushing Say

Growers who support flushing hydroponic plants say that it is crucial to rid the plant of excess nutrients before harvest, or else the final product will end up tasting like chemicals, the smoke will be harsh, and consuming these substances is not exactly healthy either.

However, many say that the real benefit is that during the flushing period, plants stop devoting their energy to intaking and processing nutrients, but rather focus all of their energy on growing bigger and fatter buds.

There is also the argument that during the last week of the flowering phase, plants go through a swelling process to grow as big as possible like a last ditch effort to survive before autumn starts.

For many plants, the flush and the lack of nutrients associated with it, may signify that the growing season is coming to an end, which may encourage the plant to increase its growth rate and output in an attempt to survive, with an increase in cannabinoid and terpene production being possible.

During this swelling process, they may stop using as many nutrients, and even release some back into the watering solution. By using plain water as the watering solution, you may encourage plants to further release built up nutrients back into the watering solution and reservoir.


What Growers That Do Not Support Flushing Say

Although this camp of thought is much smaller than those who support flushing during hydroponic growth, there are also those who do not. 

Some people say that depriving cannabis plants of their vital nutrients during the last few days of growth is a mistake. This is because for the plant to grow as many large and potent buds as possible, it needs all of the nutrients it can get.

Remember that in a hydroponic system, nutrients will run out in just a couple of days, so this is a very real risk if your timing is not on point.


The Debate on Flushing in Hydroponic Cannabis Cultivation

According to some articles, such as the study published on ScienceDirect, the practice of flushing hydroponically grown cannabis plants—aimed at eliminating residual nutrients and chemicals by exclusively watering with plain water before harvest—sparks considerable debate within the cultivation community. 

This research sheds light on the widespread use of chemical fertilizers and growth regulators among growers, particularly emphasizing the systemic nature of plant growth regulators (PGRs) that flushing may not effectively remove. 

Highlighting the complexities and uncertainties surrounding this cultivation technique, the study calls for further investigation to evaluate flushing’s real impact on the purity and safety of the final cannabis product. This article contributes valuable perspectives to the ongoing discussion on whether flushing is a necessary and effective practice in hydroponic cannabis cultivation.


How to Monitor the Amounts of Nutrients in the Water Using Growee?

Growee is a smart platform that allows for the effective monitoring of nutrients in the water of hydroponic systems. For instance, the Growee Hydro Master acts like a smart pH meter and EC meter that is connected to the internet and takes constant measurements of EC levels  and pH level in the water, so you know exactly how many nutrients are always present.

You can program the Growee devices to deliver a specific amount of nutrients to your plants through the hydroponic system. 

In the case of flushing, you can set the device to not provide the plants with any nutrients at all, thus making the flushing process much easier, faster, and more reliable. Growee systems are fantastic for accurately controlling EC levels both and  pH and for your hydroponic systems, all without the grower having to do any substantial work.

Flushing Hydroponic Plants – Final Thoughts

Although there may be some who claim that flushing is not a good thing, the vast majority of growers agree that flushing cannabis and other hydroponically grown plants is necessary. It removes excess nutrients from the plant matter and results in a much cleaner and tastier final product.


If you want the quality of the final product, whether cannabis or cilantro, to be high, then yes, flushing is necessary, as you don’t want excess nutrients being left over.

If you don’t flush your hydroponic plants, when you harvest them, they’ll contain high levels of nutrients and fertilizers, which you end up consuming, whether by ingesting or smoking. Over the long run, this may have negative health effects.

Depending on various factors, a hydroponic system should be flushed every three to four weeks, as this helps to keep the hardware and plumbing from becoming clogged or suffering from buildups.

With a hydroponic system, because the nutrients deplete so quickly, flushing just two or three days before harvest is recommended.

There are some theories that flushing cannabis before harvest may increase yields by causing the plant to put more energy into bud growth instead of nutrient uptake, but the real benefit is getting rid of excess nutrients that you would otherwise consume.

There are some theories that flushing right before harvest can increase terpene production by causing the plant to focus more energy on terpene and bud production rather than nutrient uptake.

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