New Research Shows Flushing Plants Before Harvest May Be Unnecessary

In a blind taste test, researchers have found that many prefer cannabis that has not been flushed before harvest.
New Research Shows Flushing Plants Before Harvest May Be Unnecessary

The results of a new research trial released this month show that flushing plants before harvest may not improve the quality of cannabis flower. The results seem to contradict the commonly held belief that flushing plants improves the taste and burnability of dried cannabis flower.

Under common, although not universal, cultivation practices, cannabis growers stop fertilizing their plants one to two weeks before harvest in an effort to improve the quality of their finished product.

“Flushing is important because it removes excess nutrients that are leftover within the plant,” explains High Times senior cultivation editor Danny Danko. “So it helps with the burnability of the flower by leeching out excess salts and nutrients.”

But in the trial conducted by RX Green Technologies, a manufacturer of cannabis nutrients and other cultivation products, researchers determined that those participating in a blind test tended to prefer cannabis flower that had not been flushed before harvest.

To conduct the trial, growers at the RX Green Technologies research and development facility in Colorado cultivated cannabis plants of the strain Cherry Diesel in a coco-based medium. During growth, the plants were fertilized with the company’s brand of nutrients. Four groups of 12 plants each were subjected to different flush times as harvest approached. Each group of plants was flushed for either zero, seven, 10, or 14 days.

Flower samples taken the day before harvest were analyzed for essential plant nutrients. Overall, there was no significant change in the mineral content of cannabis flower as a result of different flushing treatments.

After harvest, the plants were cured and tested for final trimmed flower weight, terpene, and THC concentrations. Lab analysis found no significant differences between the different flushing treatments for flower yield, THC potency, or terpene content.

Samples of cannabis flower that had been subjected to the various flushing times were also distributed to cannabis industry experts so they could rate them on smoking characteristics and flavor. Stephanie Wedryk, Ph.D., the director of research and development at RX Green Technologies, says she wasn’t sure what the outcome of the experiment would be.

“I did not know what to expect going into this,” says Wedryk. “I had talked to some growers I know and all of them had experience with testing flush times and not flushing and all of them only had negative experiences when they did not flush.”

Flushing Shows No Benefit

But when the data from the blind tests were analyzed, the researchers discovered that the participants tended to prefer the taste of the flower that had not been flushed at all, although overall, the duration of the flushing period had no impact on flavor, smoothness of smoke, or color of ash. In the results of the study, RX Green Technologies wrote that the trial indicates that “there is no benefit to flushing Cannabis flower for improved taste or consumer experience.”

Wedryk says that while she doesn’t think that cultivators should overhaul their practices based on one trial, she does believe that growers should be open to trying new things.

“I would definitely recommend that growers play around and find what works best for them. I talked to a grower at the event who doesn’t flush and he’s perfectly happy with his product,” explains Wedryk. “Everybody has their own unique system and there are so many different components that go into growing. What works for one grower because of their unique set of circumstances might not work for the other grower.”

Danko agrees, noting that growers who are careful not to use too much fertilizer may need little or no flushing time for their plants.

“Really, flushing is an extension of the fact that most people are over-feeding their plants,” says Danko, advising growers to feed their plants lightly, in many cases at lower levels than recommended by nutrient manufacturers.

“It’s always easier to bump up the nutrients when you see a deficiency than it is to remove nutrients when you’ve overfed,” he says.

Although Danko still recommends that growers flush their plants prior to harvest, he supports efforts to examine commonly held beliefs in a controlled scientific setting. Wedryk agrees, explaining that “as more and more research comes out in cannabis, I think we have to question some of the things that we think we knew and see if these still really hold or is it a new day?”

Wedryk says that RX Green Technologies plans further research into common cultivation practices, although she declined to offer any specifics.

“Stay tuned,” she says.

  1. Wow this is some stupid shit.
    “Stephanie Wedryk, Ph.D., the director of research and development at RX Green Technologies, says she wasn’t sure what the outcome of the experiment would be.”

    You have a phd yet you are too dumb to know basic plant science. People like this end up with high paying jobs yet those of us who are real experts are shunned because we lack degrees, but yet have 30 years of experience with cannabis and infinitely more knowledge.

      1. Do you know what a chemical is? Did you know that oxygen is a chemical? That’s right. And Hydrogen too. Are you also familiar with the combination of two hydrogen atoms with one oxygen atom? Yup – it’s the chemical compound we here on earth call WATER. Good luck living without chemicals. Science – 1; stoners – 0.

        1. I think the OP is referring to synthetic (or organically derived) mineral salts sold in plastic bottles and shipped from halfway around the world. And I agree, there’s no need for them.

    1. I think she was playing dumb cause, she didn’t want to ruffle any feathers so to speak , to all those out there that have been drinking the kool aide for to long.
      Tons of nutrient companies that have “ flushing agents “ money grab” I just never believed in starving a plant on its last weeks .
      Never did it in any the gardens I’ve grown food in over the years , why do it to my flowers 🤦‍♂️

        1. The jury is still out. It was only one experiment, using only one strain, grown one way in one medium. More research is needed. The current implied possibility from the test is that if you have truly dialed in your nutrient additions where no unnecessary nutrients have been added, you could in theory skip flushing entirely (or significantly reduce how long you flush). We are on a whole new frontier of learning, now that spreading legalization is making it easier for such research to occur. I look forward to new knowledge.

          1. Well said. I think it’s also important to note that this study is only surveying a relatively small group of people’s subjective opinions of taste from smoking. Smoking doesn’t not impart as strong or discernable of flavor as vaporizing does, so they really should have included that.

            Also, just because a bunch of stoned ppl don’t taste a difference doesn’t mean that there is not a health benefit to properly flushing. I know I’d rather consume buds that don’t have traces of these chemicals in them.

        2. Flushing doesn’t do a damn thing. You can’t remove the nutrients from the plant by flushing the soil. It just doesn’t work that way. It’s like showering removes toxins from inside your body. Think about it. What is the purpose of the nutrients? To GROW your plants. Nitrogen is converted into protein, so you can’t flush it out. It’s no longer nitrogen in an ionic form.
          As far as potassium; it’s involved with enzyme activation within the plant, which affects protein, starch and adenosine triphosphate (ATP) production. The production of ATP can regulate the rate of photosynthesis. It also cannot be flushed from the plant, only the roots and surrounding soil.
          Phosphorus plays a key role in photosynthesis, the metabolism of sugars, energy storage and transfer, cell division, cell enlargement and transfer of genetic information. It is responsible for the growth of the plant. It cannot be removed from the plant, only the roots and surrounding soil.
          Based on these facts provided by reputable cooperative exchanges and universities, flushing should have little if any affect on quality of harvested cannabis.

          1. Wow ive heard it all. Stand in that shower for 2 weeks drink water and tell me if you pee dirty. It is, and i dont discredit any other steps for they are all crucial, essential. It just does not smoke right. Dont be so gullible. Do you believe everything you read? I’m baffled High Times would even consider flying this kite. Respectively, it is a crock of shit long story short.

        3. as long as your not going crazy with like a 2200 ppm in hydro…like we did back in the 80s…..and are using say 75% of manufacturers if liquid and say 50% of higher concentrate powders….really cutting the calcuim on week 6 and try not to be dropping in lotsa chelates and your fine with a weak flower to finish……ill be honest ive tried to flush but buy day 5 the leaves inside buts start going yellow….and well i dont want it and thus suddenly forces me to dig to trim it vs this tipping spin i would normally do lol

        1. nature doesnt flush….it changes the soil PH lol and in doing so locks out the calcium and nitrogen….which is the major part that i would suggest be flushed from cannabis…calcuim should be gone by week 6 anyhow and nitrogen in late formulas is amonia nitrate which iis very ionic once its aq and disipates fast if not used…..

      1. What’s the most growlers or like 10-year-old they get something in their head, and no matter what they can’t change it, for example, scientist at NASA have proven plants cannot take any energy from light after 16 hours, it’s just a fact growers still use 18, giant children

    2. Not as stupid as your comment, most Ph.D holders are not paid well, there are exceptions like with her being a R&D Director she likely earns good money. Most graduates go into teaching some write books or research. She also had to prove that she was an expert, with 8+ years of school, using science, writing a thesis, having it evaluated and then defending that thesis from attack by the thesis committee.

      You are probably shunned because you are a contemptuous arrogant overbearing know-it-all who hasn’t put the time, effort, money, or research into getting even a 4 year degree. Yet you feel entitled to pass judgement on someone who has. There is also a reason they say “indicates” if you’re such an expert pull up the paper and replicate the study and have it published, hell write a book too. You don’t have to have a degree to do any of those, until you do though I would sit down and shut the fuck up.

      In case anyone is interested here is what her thesis was on “Management Strategies for Weed Suppression during Transition to Organic Agriculture” and here is her linkedin which has some of her published studies in it.

      1. organic farming science ambassador? 95% of poeple use un organic food, you can clearly see darker ash and in many cases not a smooth smoke when not flushed correctly, indicating your smoking something thats not present after fushing, why would you promote smoking non-organic material?

        1. You’re a dumb shit if you think flushing has any effect on ash color. Go research what causes the color of ashes, it’s temperature and duration of burning, has nothing to do with flushing. Dumb shit.

          1. @nostra, vaccines first off have been around longer than youve been born. Secondly, you linked a youtube which says to me you are gullible and easily influenced..kinda sad you base your crap off youtube.

            Maybe stop believeing everything online….its not always correct. Youre that mom that tries super hard to fine one little line that has negative effects, when theres millions of lines with positives.

        2. Yeah, chlorophyll and water. All flushing does to the actual flower is accelerate the dry/cure process by straving the plant. If dried correctly and cured correctly there is no issue with ‘black ash’ or ‘crackling weed’. Basic botany will tell you that not feeding a plant does NOT remove anything from the flowers. In fact, if a plant is deprived of nutrients in late stage flowering ot will take all of the mobile nutrient ions available in the biomass of the plant and send them, guess where, the flowers. Flushing to remove anything from the actual plant is bro science at its worst. The only thing you can successfully flush is the grow medium.

          1. I was under the impression that was the whole point of flushing. To starve the root uptake so the plant pushes its leaf reserves into the flower and induce the “fade” that is actually the beginning of the cure to reduce chlorophyll “hay” smell and scratchy throat smoke.. 6 of 1 i guess

        1. I have. But I’ve seen many dumb fucks there too. I know many who has great knowledge on certain fields and put some to shame with college degrees.
          Don’t ever feel bad Holdy regarding that. Deep down you know degree doesn’t necessarily makes you more knowledgeable. My 2c.

    3. Wow, you seem knowledgeable, well-reasoned and not at all a resentful loudmouth who doesn’t understand how scientific research works at any level.

      1. And by the way, your 30 years of smoking weed doesn’t make you any more of an expert in plant science than drinking beer for three decades makes you an expert in organic chemistry.

    4. Let’s try to be less hasty with the nasty comments. They do not help anyone. She was being objective and signalling an openness to the possibility of an unexpected outcome. That’s exactly what you want and should expect from someone with a science Ph.D. If she already knew what to expect then why have an experiment in the first place?

      I remember years ago once saying that someone should come up with a simple and easy way for businesses and individuals to update the public in real time online (weekly, daily, hourly, whatever) on the status of whatever they were working on. People told me it was a dumb idea and not possible. A year later Twitter made its debut. Let’s all stay positive and remain interested and involved in whatever new developments modern research may provide us. Of course there will be some bad things, but we should always remind ourselves to work towards the greater good. Twitter is often annoying and lame, but the good it can do has in no way been diminished. I hope you’re doing well and stay safe and happy.

    5. Wow. Just wow. The worst thing that can happen to a study is a scientist with a set mind. It compromises all results. Like yours. You’ve been using the same method for years. Forgive my bold prediction, but I don’t think you’ve ever done a double-blind study on the subject. “I’ve had a feeling for 30 years” cannot be called science in any way. You have done the flushing, payed good monye for it, so you want it to be true. Take a step back, breathe and really think: Is what I’m saying a reflex-contradiction, or do I have any objective evidence to back it up?

    6. This is exactly the kind of article what makes the people with no knowledge on this field confused. Where is the break down on what nutes we’re talking about? Organic or inorganic? I never flush my organic grow just stop feeding them 2 weeks prior harvest. However I would never smoke – or make any use of – cannabis which was grown with salts and there’s even a slight chance that I will smoke some chemicals with it.
      If anyone wants to kill themselves slowly, be my guest. I sure won’t.

    7. Well you don’t need a degree to run a blind experiment. The proof is in the pudding, the smokers preferred the quality of non flushed buds. So regardless of how experienced you are, the test doesn’t lie. If you take 20 people and give them 3 pizzas to try and the results show the majority preferred the one that was with the cheapest ingredients, your opinion doesn’t mean anything regardless if you know the other one is better

    8. OK, if flushing marijuana plants prior to harvesting the buds is fruitless and useless, then please explain why some bud I’ve seen is near impossible to keep lit when smoking it…and it has this perfumey taste to it…like smoking the dime bag your Mom had hidden in her purse in ’70’s…be like, “Ew, what’s this Chanel No.5 bud?” II’m not sure how much difference flushing does to remove harmful elements from the bud, but I do know that the way you dry & cure your weed plays a huge role in the way it tastes, how smooth it is, and how nice it burns…usually the colour and texture of the ash indicates residual elements from the fertilizers. I use Final Flush…if flushing is not effective, then at least I know it still washes out the salts of my Promix Mycorrhizae soil mix so I can reuse it again.

      1. well the back burn is chemicals…..but it is because they were inherently over feed through out the cycle….and may not be using a cannabis specific blend that drops the calcium on week 6 … for perfume and such well that is also likely due to the many factors involved in indoor heat humidity air light water feed…..were not done correctly and well the plant didnt get what you want because it was never that healthy….the sad part is truthfully you can get a nice looking but in dirt so bad that the finished root size is a beer cup…because of alot of flushing….but it will also likely be crap…..because its not plants we grow ….ITS CRYSTALS…..and those crystals require perfectness lol

    9. 34 years here. And I find the “textbook botanists” working in the “legal industry” aren’t experts in growing this plant I know intimately. I have heard 4 years experience is equal to one year of schooling so in that case I have a masters degree in cannabis cultivation.

  2. If the duration of the flushing period had no impact on flavor, smoothness of smoke, or color of ash it seems to me that the benefit of flushing or stopping nutrients two weeks before harvest would be that your not paying for unnecessary nutrition. Why give it nutrients if its literally doing nothing if not to sell more nutrients? You want the plant to use up the nutrients it has stored, this is the idea that I understand behind stopping nutrients at the end of harvest

    1. Good point. And like the article said, many people over-feed their plants, so they might have inadvertently created the need for flushing in the first place. But back to your point: if the plant doesn’t need the added nutrients for the final week or two anyway, you might as well flush if only to conserve the nutrients you paid for.

    2. haha no brainer, same results basically with 2 option. free or spend money, if i pull one down that aint flushed i get moans off people, they can tell with out me saying anything which show me if you know your shit you can see if its been flushed, there are a few dodgy products (forcers) pest control sprays on the market, with carcinogenics that have banned, but people may still have them lying around that they could have in high concentration, last thing you want on your lungs

  3. Here is another prime example of let’s ask Mother Nature …
    Does she flush everything in nature prior to giving you strawberries to avocados, to leaf lettuce? Hell no and never has , the nutrients are still right there in the earth 100% , so Danko and all the other folks can keep believing the misinformation they been peddling to us for generations.<blockquote>

    1. Actually most harvest times are in fall when rains are increased and with cannabis that is especially true. Harvest for Indica is generally in the monsoon season, increased rains, flushing. Seriously, check yourself, you are the one spreading misinformation. All of the plants you listed are not cannabis, they are not even in Cannabaceae, so any information regarding their growth habits or fruit formation would not be pertinent. I had to make an account just to comment because your ignorance defies logic. You’re the type of person to not vaccinate your kids or eat “GMO” because it is “unnatural” which isn’t even remotely true.

      1. you are right it rains and you’re the type of person that would vaccinate your kids, do you know exactly whats in the vaccine you are pumping into your kids? here is a link to some very disturbing news my friend from a scientist called judy mikovitz saying otherwise! one piece of a VERY corrupt puzzle, just keeping watching the news everything will be ok

        1. Dude, check your facts. Her methodology was sloppy and when noumerous other teams were unable to replicate her results, she was fired. She was not arrested for her thesis (that’s pretty much impossible unless it directly harms someone) but for taking a laptop with sensitive data from the lab. Apparently she got pissed, or tried to milk the story, so she twisted a lot of stories.
          Anyways, how did we get to anti-vaxxers on a discussion about watering plants?

      2. ” Actually” my ass, Gtfoh your backyard is not our model. Soil moisture conditions vary at harvest time in relation to geography. Soil growers who are sophisticated enough to be relying on soil biology arent about to kill off the microbes to shut down metabolism and nutrition cycling

    2. The difference in your statement is, nature does not receive chemically made nutrients and nature doesn’t grow it itself in self contained pots.

  4. Keep in mind these test were conducted in a controlled setting were there wasn’t any overfeeding. And second why do people ph there water for flushing isn’t that a waste of time being the whole point is for the plant not to pick up any more nutes?

  5. The importance of constant pH control is based on the knowledge that throughout the entire life of the plant there are always natural chemical reactions taking place that affect the final outcome of the grow. These chemical reactions can be helped or hurt by the pH of water and soil, so in order to allow for these natural reactions to take place unhindered, it is important to always maintain a desirable pH level throughout your grow.

    I’m sure you could get away with a certain amount of cutting corners, but there is a limit to how many shortcuts one can take before crossing the line from awesome to great; great to good; good to okay, and okay to not good. I have experienced numerous growers’ finished products and the results were always dependent on the knowledge, skill and dedication/patience/love of the individual grower. To paraphrase James Brown, you have to pay the cost to be the boss. Even those with natural talent have to work hard to excel in their field (no pun intended).

  6. Since there is no real difference, besides a few people talking about taste. I think I’ll just water my plants the last two week. Yes the last two weeks I give my plants tap water at a pH of 6.5. Since I grow in soil, I don’t call watering my plants the last two week flushing, its just watering.
    Moral of the story: my weed just as good or better than yours and I save 2 weeks worth of nutrients.
    Last note your lights are feeding your plant not fertilizer. If all you do is grow in a good well balanced soil and water with water at a pH of 6.5 you will produce a decent sweet tasting crop.

    1. Ya so true. An analysis of the compounds released on combustion along with experiential data would be legit.

  7. je ne suis pas un scientifique,et encore moins un expert,j entretien aux 2 semaines,avec 15,30,15,de nutri,arroser avec amour,entretenue a tout les jours,(feuilles,insectes, je recolte en mi-sept,jamais eu de problemes,je n ai jamais,rincer,,.chaqun sa facon j doit avouer que je ne connaissait pas cette facon de faire,et tant mieux si cela fonctionne pour vous.bonne journée,et amuser vous.lolll

  8. there is a obvious bias on the side of “use more nuitreients” proably beacuse these “scientific studies” were done by a NUTRIENT COMPANY” and a phd will not nessesarly make you anything at all sorry to the people who wasted tbeir time and money going to school for 8 years, your frustration clearly shows

  9. Flushing is a waste of time, money and water. Living soil makes the best tasting smoke on the planet. Try a chemically grown or hydroponics tomato up against a living soil one. It will blow your mind. East Texas has the best tasting tomatoes on the planet because of the iron in the soil. Fruit, vegetables, and herbs get alot of their flavor from the soil. Why is it that only pot growers flush the soil. Do tobacco growers flush their fields. No. I personally have never flushed a pot plant before harvest and I have grown top shelf smoke since 1969.

  10. Dumb shit this, ignorant so and so, get a degree, write a paper, etc. It sounds like the Russians want this to blow up! Why not take a small hit from your last grow, relax, and contribute sanely without blowing the subject out of the water. I have plants growing, will a couple this way and that way. See where to go from there and keep reading online.
    Both sides, stay safe!

  11. the reason is because they flushed the plant to much, they said for 14 days, u supposed flush it once or twice and wait both times for it to dry fully and then harvest

  12. The study was poorly designed. The sample sizes weren’t large enough to warrant the conclusions. The “experts” can’t be an objective source of information. Their opinions are subjective. Interesting study but far from conclusive. Also, when will RX Tech release the raw data? Until then we have to take their word for it.

  13. The first thing that needs to be looked at is Who funded this research? A nutrients company and Guess What? They want you to use as much of their product as possible in every run. So feed them plants heavy till you harvest. NOT Wait till you put fire to it. Lots of real pretty bud turns real UGLY when you put fire to it. Why is that?

  14. First of all as a grower for over 20 years I’ve hit the best quality and weight by flushing ever 4-5 days and then flushing for 14 days. In hydro flushing resets the plant from lockouts that occur during the flowering cycle. Lockouts cause plant stress which lowers yield and can turn flowers darker. Try putting pgr and running heavy nutes and not flushing. And tell me how you do.

    1. That’s not what lock out is…..
      Lock out is simply when nutrients get “locked out” because they are made unavailable at certain PH levels.
      Simply make sure that your plants nutrients are at the proper PH levels(Between 5.0 and 6.5) and you will not get lockout. Nutrients at those PH levels are most readily available to the plant. I suggest getting a PH/Nutrient conversion chart to help you understand better.

      My plants go through a 5 gallon bucket of water every other day, the PH drifts through the day as temperatures of the nutrients change because of heat from the lights.

  15. I call BS. … smoke unflushed bud and look at the ash…. the ash will be black cause your burning nutrients and chemical bud… now do the same with flushed cannabis and look at the ash… it will be white if properly flushed. Because there is little to no chemicals in the bud being burned and inhaled… that’s the simplest research anyone can do.. ALSO bud that hadn’t been flushed sometimes gives you a headache and a not so good feeling high..

  16. It’s probably wise to stick to what works for you! In my case I legitimately use no Dead Nutrients!!! Minerals and highly aerobic teas for feeding in northern Maine. Verdict from veteran smokers is. The taste is great and the high is smooth. But calling people dumb is naive. Just because you don’t have a PHD you assume that someone with intellect should know the results of an experiment. That’s not how science works at all!!! You have a hypothesis and then you try every way imaginable to make that hypothesis not be true. Why are people so rude!

  17. sounds like nostrafckingdarmus has a stroke coming his way. You need to relax bro and get a volcano hybrid. Your opinion is no more valid than everyone else’s so just take it easy.

  18. people preferring unflushed because you get a more a choke and they think they get higher. you still need to flush, people don’t because of yield loss. If you don’t flush and you smoke it the day after you bag it, you get more of a headache than flushed bud. Simple as that, do that test yourself and find out the truth. if you don’t see the truth than you dont smoke much.

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