Flushing
Interview: What Is Flushing and What Does It Really Do?
Caller: Hey Aquaponic Dumme, I keep hearing growers talk about “flushing” before harvest. What exactly is flushing, and does it really do anything?
Aquaponic Dumme: Flushing is one of those topics that’s been debated for years in the cannabis community. In simple terms, flushing means running plain water through the growing medium near the end of the plant’s life cycle to remove excess nutrients. The idea is that by depriving the plant of nutrients, you can improve flavor, smoothness, and overall quality. But the science behind it is more complicated — and often misunderstood.
Caller: I’ve heard Dr. Bruce Bugbee talk about flushing. What’s his take?
Aquaponic Dumme: Bugbee has discussed flushing, but it’s important to remember that he works primarily with hemp, not cannabis. Any information from him has to be viewed through that lens. He’s mentioned studies he’s done, but none have ever been published or peer-reviewed, which means there’s no verified scientific method behind them. I also suspect the data he refers to is quite old.
What Bugbee has said is that flushing can be seen as a form of precision nutrient stress — specifically, nitrogen deprivation. He’s described it as a way to reduce nitrogen levels late in the plant’s life to potentially improve quality. In his words, nitrogen is a key element that helps make proteins and chlorophyll, so reducing it can stress the plant in a controlled way. He’s suggested that this might slightly increase cannabinoids — around 15% in some cases — and can also bring out more purple coloration in flowers due to reduced chlorophyll and increased anthocyanin expression. However, he also warns that it must be done carefully to avoid yield loss.
So, while Bugbee’s comments are interesting, they’re not based on peer-reviewed cannabis research. They’re more of a theoretical framework for nutrient stress management.
Caller: Most people online reference RX Green Technologies when they talk about flushing. Is that the main study?
Aquaponic Dumme: That’s one of the biggest misconceptions out there. RX Green Tech’s study is not the gold standard for flushing research. It’s actually one of the smallest and oldest studies — about six years old now — and it’s self-published by a for-profit company. That means it didn’t go through the peer-review process that ensures scientific credibility. Their methods were vague, and they didn’t clearly describe how they conducted their trials, which makes it hard to evaluate their results.
As of 2025, there are five published studies on flushing. One was done by a student, three were peer-reviewed and published in reputable journals, and RX Green Tech’s is the only one that wasn’t. The newer studies are much larger, more detailed, and far more reliable. They also explore how flushing affects cannabinoid profiles in specific cultivars — something RX Green Tech didn’t address.
Caller: So what do the newer studies actually say about flushing?
Aquaponic Dumme: The most recent data suggests that flushing can have several measurable benefits when done correctly. It’s not just about removing nutrients — it’s about managing plant stress and improving post-harvest quality. The studies show that flushing:
Promotes fall colors by reducing chlorophyll and allowing other pigments like anthocyanins to show.
Is good for the environment, since it reduces nutrient runoff and waste.
Saves money by cutting back on unnecessary nutrient use late in the cycle.
Has been shown to improve cannabinoids in certain cultivars, depending on genetics and timing.
Speeds up curing and may improve taste by limiting chlorophyll content in the final flower.
Caller: So flushing isn’t just about washing nutrients out of the soil?
Aquaponic Dumme: Exactly. It’s more about precision nutrient stress — intentionally reducing nitrogen and other inputs to trigger specific physiological responses in the plant. When done properly, it can enhance color, aroma, and cannabinoid concentration. But it’s not a one-size-fits-all process. The cultivar, environment, and nutrient program all play a role.
One of the more recent researchers on cannabis flushing, Dr. Nirit Bernstein from the Ministry of Agriculture in Israel, summarized it perfectly:
That statement aligns with the broader findings of the newer research — flushing doesn’t harm the plant, can sometimes improve cannabinoid content, and offers both economic and environmental benefits.
Caller: So the bottom line is that flushing works, but it’s not magic?
Aquaponic Dumme: Exactly. Flushing isn’t a miracle cure, but it’s a useful tool when applied with understanding. It’s not about “washing” nutrients out of the buds — it’s about managing nutrient stress to improve quality and efficiency. The science is evolving, and the newer studies are giving us a much clearer picture than the older, smaller ones ever did.
Based on research as of 2026, I too, recommend flushing as a beneficial standard practice for cannabis cultivation. While it does not drastically alter the plant’s chemical profile in every case, it provides clear economic, environmental, and qualitative advantages when done correctly. Keep in mind that more research is being carried out every day, and as the science continues to evolve. Perhaps recommendations may be refined over time, but as of 2026, this is the best-supported approach for healthy, efficient, and high-quality cannabis production.
References:
Stemeroff, J. (2017). Irrigation management strategies for medical cannabis in controlled environments. Doctoral dissertation, University of Guelph.
Wedryk, S., Wall, T., & Bennett, R. (2019). Cannabis Flushing Research Study – Impact of different flushing times on quality and taste in Cannabis sativa L. RX Green Technologies.
Hershkowitz, J.A. (2024). Nutrient Management of Cannabis in Controlled Environments.
Saloner, A., Sade, Y., & Bernstein, N. (2024). To flush or not to flush: Does flushing the growing media affect cannabinoid and terpenoid production in cannabis? Industrial Crops and Products, 220, 119157.
Ruangrit, S., Sutjaritjan, K., Chokchaisiri, S., Meeboonya, R., Wonganan, O., Sripan, P., Yongram, C., & Roongpisuthipong, A. (2025, January). The Pre-Harvest Flushing Effect on the Phytochemical Composition and Antioxidant Activity of Cannabis sativa Fluorescence, Leaves and Twigs. In International Academic Multidisciplinary Research Conference ICBTS Beijing 2025 (pp. 200–206).
