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Flushing & Leaching & Final Bud Swell

re: Flushing & Leaching & Final Bud Swell

Well you bring up good points. Yes "flushing" will wash out EXCESS nitrogen and EXCESS salts... not from the plants roots and not from the plant. The plant will ONLY uptake what it needs for growth and that's it. So if you put in extra nitrates, whatever the plant doesn't need and the soil cannot hold on to with CEC (cation exchange capacity), yes that extra will wash out into the water table. The water that you and I need to use for potable water, it goes into the local water shed in the form of nitrates... there's all sorts of reasons why we shouldn't do that but thats another topic.

So we pollute the environment we live in the excess nitrates. That is a fact.
While we are at it, we are also killing off the microbiology in the soil that helps our plants grow.
So we put into the soil, nutrients in a form that can be directly absorbed by the plants roots bypassing the natural organic way plants uptake nutrients.

This is where the taste comes in (or lack of taste). Plants that grow with man made soluble nitrates that feed the plant and skip the natural cycle do not taste as good as plants that are grown organically. It will be the same with cannabis.

To experience what I'm talking about, go to your local food store and buy organically grown fruits or veggies; buy one of each, organic and one that is grown conventionally (with man made nitrates ect.). Eat them side by side... guarantee you can taste, smell and feel the difference with organically grown tasting much better.

Ok now lets go back to the plants that are grown with chemicals. Since we skipped past the natural cycle of soil microbes breaking down the nutrients for the plant in the symbiotic relationship the plants have with soil microbes guess what else happens. The plants immune system is not as strong as it should be and now enter pests and disease. Now we need special chemicals to fight off pests and disease. Ok so now we need to spray plants with pesticides etc with compounds that were never tested to be smoked by humans.

Getting back to the "flushing" ... the only accomplishment we achieve by this process is washing out excess nitrates that cannot be adsorbed by the soil or absorbed by the plants roots. No effect on plant other than probable damage to the root system.

So why waste the water.. it would be far better to use less fertilizer so there's no excess build up and water the last 3 weeks of growth.

I have a question. What do you folks do with soil after harvest that you grow in and use fertilizers on??
Im throwing it away. Soil is cheap


New Member
re: Flushing & Leaching & Final Bud Swell

I understand flushing as not only to remove excess nitrogen and salt build up (although this is correct) but also to begin to break down the chlorophyll and remove that grassy smell from the final product, resulting a better taste and better burn. I am currently experimenting with this... I shall keep y'all updated with what I find. :)


Grow Journal of the Year: 2017 - Grow Journal of the Month: Sept 2017


Well-Known Member
re: Flushing & Leaching & Final Bud Swell

I have learned and use several techniques towards the end of my grows to help swell the resin glands and almost quadruple trichome production. It's a old techinique I have mentioned on here before (around the formus) in guidling and helping people get the most out of their crop... The last 2 weeks of flush is standard. No matter what you grow with or how you grow it. That simple. BUT, in the last 48-56 hours of the plants life another "technique" I use comes into play. I switch the humidity down to 25-32%, then hit em with a 8/16 light schedule. This 8 hours of light and 16 of dark sends the plant into HEAVY Trichome production and swells the resin sacks to the size of grapes. In most cases (with me) the trichome production AT LEAST triples. I also in the last 48 hours like to make a cut at the base of the plants stock. A simple cut half way through the stock or a little less will send this plant into even heavier trichome and resin production. The plant thinks it's being eaten by a deer or animal and when you hit them with the 8/16 sched... Man o Man. It tricks the plant into thinking it's day is defiantly numbered by insinuating winter is upon her and shes getting eaten... These techniques towards in the last 48-56 hours will not only help you get bigger stickier buds. But it will also give you substantial increase in potency. BUT, do not let it go to long or your plant will nanner. And we obviously do not want this. This is why I say the last 48-56 hours. After many tests I find this is the "sweet spot" and wont deal with any nanners. ;):Namaste::thumb:

PSS: Since this post was about the ending "techniques" used in harvesting cannabis, I thought I would "expose" a few more secrets used by master and advanced growers world wide. :Namaste:
heck ya drop that RH !!


re: Flushing & Leaching & Final Bud Swell

Gonna hit this in a moment.

Hey there arteekay, thanks for the defense there, you hit everything on the head. Every one of the well known cannabis gods has mistakes, retractions, and in some cases full on contradictions. Ed Rosenthal, Jorge Cervantes, Ryan Riley, that dude you guys named and I haven't looked up yet.

Besides flyboy, you say the big reason we need to flush is because most growers use too many nutrients. You claim to have been growing for 17 years, and you flush every time. This tells me you haven't learned to feed your plants properly in the 17 years you've been growing them.

But, beyond that, back to the facts and evidence.

So, yes, the question of good analogs to Cannabis flowers. You're right, flowers aren't leaves, so there should be a difference, and in my opinion, based on my knowledge of plant physiology, I find it far less likely that excess nutrients are being put in the flowers, much less, that they're being taken back out, or used up.

Flowers are sinks. This means they receive, they don't send. They receive nutrients based on concentration gradients. They receive most nutrients as amino acids, sugars, and carbs. Not as raw, inorganic elements, such as N. They don't store energy, at least not for use by other plant parts.

Leaves are a whole other story. Leaves are both sources and sinks depending on where they are in life. At harvest, tobacco leaves are sources, though failing ones. You pull tobacco leaves as they begin to senesce, losing much of their nitrogen to younger leaves. Leaves are a place where flushing would make sense to me, as mobile nitrogen is still present, and can still be removed from the leaf.

In a flower, there's just no identifiable way to remove "excess" nitrogen, or anything else. No way I've seen identified, at least.

But, while the flower and leaf are very different in purpose and fynction, the way they burn is pretty damned similar. So, here's some science. It proves nothing in the way of flushing being useful /useless, but it does challenge some of the purported evidence of it being of benefit.

Many cigar aficionados also believe there is a connection between quality and ash color. Most also believe white ash to be best.

Yet, Cuban cigars, kind of the gold standard of cigars, produces a BLACK ash. This has been attributed to VERY LOW levels of, haha, insert element here.

Some say low magnesium. Some say high potassium. Nobody ever mentions nitrogen. Some say black ash is bad, some say good. Here's a site that says black ashes are bad, because it means the soil contains LOW levels of nutrients.The Ash Knows...

Of course, they're all guessing too, maybe based on a tidbit of science.

How about the levels of elements found in wood ash. Most agree wood ash is mostly calcium of some form(white,) followed by carbon (pure black, naturally,) and then some trace amounts of heavy metals.

Nitrogen generally isn't found in ashes. Potassium certainly, but not nitrogen.

Interestingly, if you have a lot of magnesium you're burning, and water is available, you may end up with ammonia and Magnesium Oxide, MgO, when burned in the presence of nitrogen (78% of atmospheric air.)

I could, but won't, dig into that a bit more to see if it's possible that this is causing the flavor issues some complain of from not flushing. Again, looks to me like improper dry/cure.

Anecdotes. Here's an anecdote for you. I just harvested 6 ounces from two plants, one flushed, the other not. Both taste the same, smoke the same, burn the same, and are both just as smooth as each other, which is very smooth. I dried this stuff over two weeks before jarring, and continue to let it progress.

I've been smoking some of the product since harvest. Here's what I've noticed.

The wet buds are harder to light and keep lit. They burn into these black masses. They honestly aren't that harsh, but there's no real flavor.

As the days have passed, the product has improved. This is from my experience, and from the experience of my wife, dad, and brother in law. It's burning cooler now, stays lit better, and the ash has consistently become lighter in color and texture. From a black lump in my bowl to fine gray ash, now at an almost white ash.

So, for what anecdotes are worth, a proper, careful, dry and cure are critical, especially compared to the concern everyone seems to put into flushing.

Of course, there are very few people marketing and selling equipment for drying and curing, so maybe that's why.
As all should know...every receiver is a potential transmitter and vice versa. Same with sinks and sources.


re: Flushing & Leaching & Final Bud Swell

Its interesting when we see the cannabis community doing things that no other commercial horticulture industry does.

do we flush our hydroponic lettuces, strawberries just before harvest so they don't taste of nutrients. hmmm no.
horticulture is my profession and im a consultant, so do find it interesting some beliefs some here have.

Since when is commercial better?


Member of the Month: Mar 2019 - Grow Journal of the Month: Jan 2020
not really... it was said well and I agree with most of the above. Flushing just before budswell is the optimum time and results in a much better product at the end.


Well-Known Member
re: Flushing & Leaching & Final Bud Swell

I understand flushing as not only to remove excess nitrogen and salt build up (although this is correct) but also to begin to break down the chlorophyll and remove that grassy smell from the final product, resulting a better taste and better burn. I am currently experimenting with this... I shall keep y'all updated with what I find. :)
I’d love to hear how this breakdown of chlorophyll occurs due to “flushing”.

To all the people who have presented this thread, and the useful data in it I thank you. I personally don’t even argue with people about the flush thing. When I tell people I don’t flush my cannabis they tend to go silent. It’s nice having this data to back up what I believe to be true. If people want to flush their plants, let them.


Grow Journal of the Month: Dec 2017 - Photo of the Month: May 2020
I'm cool with people doing whatever they want.

Have at it, flushing it's just not what people think it is.

All I'm saying.

It's a bad term.

Should call it water only for the last 2 weeks or something like that.

That's all it is. Has very little to do with nutrients, plants or soil.


Well-Known Member
Yep, flushing is mostly just psychosomatic, you think it is therefore it is.
It literally can't do anything to the bud itself, it could move mobile nutrients from the leaves but they go straight to the bud.
The most one could hope for by flushing is removing salt buildup in the soil so that roots can uptake more water and transpiration happens more freely.
With a salt buildup in the soil you get a sort of reverse osmosis, the soil actually leeches water from the roots.
But you're starving the bud right at the point of bud swell , usually the last two weeks of flower is when the buds fatten.

If you want great tasting bud theres only just one way to get that really.
First you grow 100% Living Organic Soil with absolutely zero introduction of any salt based synthetic nutrients.
No flushing at all because basically your whole grow is a flush.
Then you do long drying time, at least 10 days hanging in about 68 degree temp, air movement in the room but not directly on the buds, in about 55 to 60% humidity which depending on bud size and thickness of stalks should take 10-14 days to dry.
This gets rid of the chlorophyll which gives the grassy or hay taste.
Then a nice proper cure at 62% humidity in a sealed jar in the dark.
Except for a few taster buds I rarely touch my harvest for at least about 2 months after harvest, 10-14 days drying and at least 45 days curing just to make it smokable.
I always have at least a few ounces on hand that has a 1+ year cure on it.
THAT, is where you get your flavor and smoothness and bone white ash.
Proper drying and curing.

J Obadiah

Well-Known Member
re: Flushing & Leaching & Final Bud Swell

I'm also starting to question the efficacy of flushing. On the surface it seems like it works. It's logical, certainly, but I'm not sure the plant can work the way described. Let me explain.

The point to flushing is to remove excess fertilizer salts from the grow medium, forcing the plant to consume it's own energy stores. I feel like this is maybe 100% functional for most parts of the plants, except the part we care about, which are the flowers.

Flowers are sinks, not sources, meaning flowers don't provide anything to the plant, it only receives. So, while it makes sense that maybe the leaves would benefit from a flush, the buds really have nowhere to offload excess fertilizer, if any even exists in an available form within the plant matter. I was also thinking that, rarely do we burn flowers with nutrients. Nutrient burn is caused by excess salts forcing water out of cells, at least in essence. If there were excess nutrients in the flowers, flowers should nute burn. But rarely do they. It appears that the vast majority of nitrogen and other elements we feed as fertilizer, are incorporated into the plant matter, not stored or just sitting, but being part of the cell, so, not something you remove via translocation.

I also joined a forum for growing tobacco. Funny, they're just as tight knit community as over here, with different strains and breeders. Cool stuff.

But anyway, these guys don't flush, and laughed their asses off when I explained it to them.

They then, after composing themselves, explained that flavor and harshness are controlled with the cure. They then described their cure methods, which jive with Ed Rosenthals latest grow guide.

Basically, we all have it backwards. We dry and cure, while they cure, then dry.

It was explained that a proper cure of any plant matter requires a period of fermentation, which begins imediately after chop. Curing without fermentation is apparently not actual curing. The cure breaks down most of the nasty plant material via fermentation, so, cells are broken down, gasses release, and any of those elements that had previously constituted the matter of the cell are released, which these guys say takes between 4 and 16 weeks in low/no light, medium humidity and temperature, with air circulation.

After the cure, they dry it to the right humidity just like us, and then age it for a few years.

No flush, no flushing agents, just a really long, true, cure.

Most of us let the buds dry in about the same conditions tobacco usually cures, little to no light, medium humidity, moderate temps, some air circulation. So, we probably are benefitting from a fairly short cure during our drying period, and if we are letting jars air out regularly (air in, actually, a true cure requires oxygen.) So, if you slow dry, and are good about airing jars out, and you do this properly for longer and longer periods, as everyone recommends, you getter better flavor, as everyone seems to say. If you're doing this, you're benefitting from a true cure.

I also found that while oxygen can degrade thc, light is a much bigger enemy, and if cured properly even in the presence of oxygen, the bud should lose very little potency.

I'm not about to bet the harvest on this, but I will be setting a few buds aside for a proper long ferment/cure. Ed says it's best. Others say the same. All of them say it's all about the proper cure, and that our traditional methods are just quick and easy. They work, but could be much better.

So, anyway, aside from our apparently not curing properly, it looks likely that flushing does nothing at all for the flowers, maybe something for leaves. It definitely clears out soil though, so at the least, you aren't pulling more nutes in.

Again guys, this is meant to be a discussion on what's actually happening in the plant. While I appreciate other harvest tips, that's not what this thread is about. In fact, it's these types of tips I'm trying to understand. Too many people just do things either because they seem to work, or at least do no harm. I want to know why it works, not just that it does.

That's how things like Miracle Grow become so popular. Anyone using it thinks it's miraculous, because they don't understand anything about plant nutrition.

Their shit plant looks great after use. It's a miracle!

No, it's just NPK.

The bud tastes better after flushing.

No, it's just the cure.

And I'll continue flushing until I am convinced one way or the other. I lean toward it not working, but the marketing guys (and at least half of you guys) have me scared to risk it for now.

I really, really appreciate you're willingness to understand the why. I am doing my best to do the same. You're questions and responses have literally come from right out of my own mind lolol nice work.


Grow Journal of the Month: Dec 2017 - Photo of the Month: May 2020
re: Flushing & Leaching & Final Bud Swell

Okay, now I'm convinced. Pre harv3st flushing does nothing as far as improving taste, smell, or smoothness of flowers. There may be some benefit to the leaves.

Overall, a proper dry and cure makes for the smoothest and tastiest buds.

Black ash is incomplete combustion, almost certainly an indication of too much water in the buds. The same thing happens when you burn uncured wood in a firepit. It's hard to light, stay lit, hisses and pops, and burns black, at least to start.

Cigar quality is sometimes judged by ash color, with the same myth, of white being better. Of course the real aficionados seem to know better, Cubans produce dark ash. Apparently, according to the cigar guys, white ash is caused by MORE nutrients in the soil.

So cigar people agree white smoke is better, but they attribute it to increased nutrient levels, not decreased.

But the easiest way to resolve this is, keep smoking the black ash. It should end up white. If so, that's incomplete combustion for you.

Just remember that the guys growing tobacco are smoking LEAVES. I'm smoking flowers. The curing and drying methods are a little different. Not a lot but a little bit.

IF you want to check out curing like the tobacco guys do it, check out COB - its been a thing for longer than history.

I cure with closed containers and use 62% Bovida packs (same as some tobacco guys do it) for the long haul.

Water added to soil with high CEC and decent amount of SOM (soil organic matter like vermi-compost) there will be very little to NO leaching of excess nutrients. The nutrients are not in soluble form so cannot leach or wash away. We can discuss how those locked up nutrients become available to plants. It doesn't have anything to do with flushing thats a "fer sure".

People that use excess fertilizer in soil, you can leach out excess salt in the form of nitrates IF you have low to no SOM and very little CEC. This type of "soil" would basically be a soil-less medium.

Horse trainers feed the horses Guinness too so it must be science.

Knife party

Well-Known Member
re: Flushing & Leaching & Final Bud Swell

What's treacle water?
I know this is a really old post .....

Treacle water is similar to molasses water and golden syrup etc it's all from refining sugar cane. It's normally slightly more refined than than molasses.

If you didn't have to deal with molasses and treacle as a child you are lucky our parents used to make us take a table soon or two of it a day the sweetened molasses wasn't too bad but the other stuff I'd compare to chewing sweetened tar


Grow Journal of the Month: Dec 2017 - Photo of the Month: May 2020
To draw any conclusions (with science), we wood probably need to see say 100 plants compared to another 100 plants - you could to a 50-50 to get a decent comparison. That would be clones of the same plant and exactly same lighting and soil medium..

And then try and be objective.

There I go with that dang scientific method again. lol


New Member
To draw any conclusions (with science), we wood probably need to see say 100 plants compared to another 100 plants - you could to a 50-50 to get a decent comparison. That would be clones of the same plant and exactly same lighting and soil medium..

And then try and be objective.

There I go with that dang scientific method again. lol
Very true. The most clones I have ever taken at once was around 220 from one plant all at once. Yeah some of the clones were not prime clones and the mother plant was being vegged under a 1000mh. When I do side by side comparisons, its with plants from the same batch of clones. When I do it with just 20 or so plants I look at the results and try it again with a new batch of clones and if I think something works better I will change or adjust my grow methods.


Active Member
Ok ive got one for everyone in regards to flushing. I had to rewrite this unfortunately, so it might not be as good as my first thought.

I understand its up in the air in regards to flushing for end results of the Cannabis Product.
I have a theory about everything that is going on with commerical cannabis users, if i may, id like to run this by everyone, as i am a new member and want to start off on the right foot.
What about the flushing in regards to the E.P.A.'s acceptable daily intake (ADI) for nitrate of 0-3.7 milligrams (mg) nitrate ion/kilogram (kg) body weight or the maximum contaminant level (MCL) in water for nitrates at 10 parts per million (ppm) (10 mg/L) and for nitrites at 1 ppm (1 mg/L) [EPA 2002; EPA 2012] .
This doesnt seem logical since we dose our plants with a ppm of 100+, which gets absorbed by the plants, then in return we ingest it.

Would it be worth it to use a Nitrate Ion Tester, to test cannabis flowers/sugar leaves/ fan leaves pre-flush and post flush, and pre-cure and post-cure?

I think this may resolve the issue with users that may be diagnosed or think they may have CHS (Cannabinoid Hyperemesis Syndrome)

I have added a few links to some supporting docments and a coincidence i fell upon this thread.



Grow Journal of the Month: Dec 2017 - Photo of the Month: May 2020
Nitrates and nitrites do get absorbed by the plant same as the plants do with organic soil. Its not in that exact form tho once a plant uptakes it. These get transformed by the plant and also moved around from place to place where needed in the plant.

Not a plant biologist here.

Look up "nitrogen assimilation by plants"
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