Flushing vs. Nitrogen Leaching

Flushing is something growers do with the notion that "the plant only takes what it needs from the nutrient supply," consuming only some of one nutrient, and more of another. Eventually, nutrients that were not consumed as much have higher ratios in the soil. Some growers claim to "flush" these excess nutrients out before harvest to get "better flavor" or "cleaner smoke." But why would these excess nutrients need to be flushed out if the plant is taking "only what it needs" from the nutrient supply?

Furthermore... how does one "flush" soil? I use amended soil and water with pure water, occasionally some molasses, from start to finish. However, my plants do experience nitrogen leaching, which is simply a natural response to the depleted nitrogen stores in the soil. But the nitrogen is not "flushed" out by water. Rather, the plant just consumed it all. Are these "flushing" growers confusing their concept with nitrogen leaching? After all, nitrogen leaching is said to result in better flavor.

And BTW, if a plant is taking the nutrients, then that means it wants the nutrients, right? So why would we want to prevent the plant from receiving the nutrition it needs for biosynthetic processes? Wouldn't a reduction of biosynthesis slow down plant development?
Isn't the goal to achieve maximum yield and maximum potency?

If we are spraking about the final flush, then, i could try to answear you fast:

You: If a plant is taking the nutrients, then that means it wants the nutrients, right?
Me: yes

But..

You: so why would we want to prevent the plant from receiving the nutrition it needs for biosynthetic processes?
Me: because the processes that you are talking about will end when the plant is dead. Far away from when you want to chop your plant. When you flush, don't think about what she need, you need to cut her after 1 week or 2 and she is only doing her's processes TILL she dies.

You: isn't the goal to achieve maximum yield and maximum potency?
Me: i don't want ti smoke some herbs that taste acid or like trash, and when the "maximum potency" is there right when you have decided when to cut, she could grow more weeks but the heads of the terpens will only get darker and the overall potency will be less daybyday.

Check with a 60x lens when they have a prosent with amber head, and from there you know at which stadium of potency you are.. If all the heads are amber and darker then it went too much time since you needed to cut her.


You:Furthermore... how does one "flush" soil? I use amended soil and water with pure water, occasionally some molasses, from start to finish. However, my plants do experience nitrogen leaching, which is simply a natural response to the depleted nitrogen stores in the soil. But the nitrogen is not "flushed" out by water. Rather, the plant just consumed it all. Are these "flushing" growers confusing their concept with nitrogen leaching? After all, nitrogen leaching is said to result in better flavor.
Me: If your plant is in late flowering, then she is taking the nutes from the big leaves not from the soil and here we can say that this is a natural event. Those leaves will fall.
But what If you cut those big fan leaves and give her water for 2 weeks?

Your plant will suck from the roots the solution, just water or feeding solution, she will suck the water and some nutes or she had to have some problems (dead, ph problems etc..)

But instead of taking that small amount of nutes from the soil, she will take them from the fanleaves and the "yellowing" process will speed up for this reason too.

For the first part, the parts will stop to take nutes when she is dead or later than when you want to chop her. And yes, dark leaves taste shit!

The burning will be smoother too, because when the leaves are yellowing, then the next step for them is to fall (the plant don't need them so they fall) and If you smoke a bud from a plant well flushed/dryied/cured she will not show you black or dark signs on the filter.
(I live in a cold place, i use to burn My wood. If the wood has been cured for a long time, then burning the remaining material will be white and it will burn better)

When curing your bud it will be lighter, because of the chlorophill, but also by Flushing and letting the plant do her job the taste and smell will be better. (Have you never tryied to eat some leaves?)

"As chlorophyll goes away, other pigments start to show their colors. This is why leaves turn yellow or red in fall."

What happen's If all the fanleaves were yellow? Where could then the plant take food from?
There are some limits. Like a previous overfertilization, If you had any over, the leaves will taste bad.

By getting a better taste/aroma, the potency and yield will still remain there is your buds. We are not talking about flush or give them only water for months.

Or is "flushing" another word for "water-logging" or "flooding"? Inducing abiotic stress (water excess or deficit) does cause the plant to respond...sometimes in a beneficial way and sometimes in a negative way.

How many gallons of water is required to flush/leach MY grow medium? Is it the same for your grow medium? Hmmmm, probably not. What percentage of your grow medium aggregates "absorb" and "hold" nutrients, compared to mine? All sorts of fuzzy logic with wild ass guesses (WAG) is what I say. If one incorporates a lot of water soluble nutrients in the regime, then what water gives--water can take away; but if one uses dry nutrients--different game.

Now, for the chin stroker--if one includes the concept of purposeful water deficit a week or so before harvest (which is the opposite of "flushing"), I submit things can really get interesting. IMO, aibotic stress can be your friend...or enemy.

Flushing, ahhhh, the good days of "I used Miracle Grow soil and fertilizers" rears its ugly head again!!!!

Nutrition levels, how you water, how often you fed, medium type..... are all factors into "if a flush is needed" .

I feed with every watering, and water to heavy runoff each time. As the plants reach week 7 of flower, their food levels are cut in half til the chop (unless a long running sat).

I dont flush, but watering til runoff each time does help pull excess salts out of the soil, which is the purpose of a flush in the first place.... To remove all those unused nutrients. This was ALWAYS a problem with Miracle Grow soil and nutrients because they use Urea as their main source of N, and that breaks down so slow for our purposes.

So, basically "flushing" refers to washing away excess solubles. Nitrogen leaching degrades chlorophyll, leading to better flavors.

So flushing doesn't actually wash anything out of the plant per say, but just washes the soil. Nothing is actually getting cleaned or cleared out of the plant itself. So, in essence, flushing is pointless unless it is to remediate overfertilization with soluble salts.

Am i right or am i right?

Here is the conflict, as I see it: If an action (adding copious amounts of water) causes a reaction (copious amounts of runoff), does it matter which term is used? Leaching, flushing, flooding, "over watering", or "inducing abiotic stress"? All those things happen.

As to "nitrogen leaching", or specifically "nitrate leaching", field studies vary but when comparing "organic" vs "conventional" (synthetic) operations, most research suggest that organic source of nitrogen causes less nitrate loss from water leaching than synthetic sources. Secondly, nitrate leaching usually coincides soon after application of the fertilizer, not at the end of the growing season. It seems that synthetic sourced nitrogen remains longer in the grow medium than organic--as evidenced to higher levels of nitrogen residue left behind in the soil at the end of growing season.

Again..., imo--what water gives (water soluble N), water can take away (leaching of N). But if I incorporate appropriate amounts (not excessive) of organic nutrient high in protein (such as a meal based fertilizer sourced from soybean, linseed, blood, etc.), then very little nitrogen remains in the soil at harvest time.

Why? Most organic nitrogen fertilizers (6% N or more) provide about 60% of their plant available nitrogen (PAN) by the 28th days after application...75% or more PAN by the end of the growing season (125 days) thus generating a potential maximum PAN residual of 25%.

Of course some organic inputs (like feather meal) provide 99% PAN by the end of growing season--while others (like kelp meal) provide only 4% PAN by the end of growing season (yep, that means 96% PAN remains in the soil at harvest time).

Hmmmm, I say.

I don't know what PAN is but I doubt it fries eggs.

The old way was to give strait water to soil or hydro for up to 21 days prior to harvest. This was for chem nutrients.

Seems today people think flushing is drowning the roots to flush out nutrients. Back in the day that was called a fuck up.

With organics there is no need to feed every watering. Outdoors there will always be rainy days. And i don't mind organics that reduced feeding N at the end. Maintenance dosing nitrogen is plenty.

Easy7 said:

I don't know what PAN is but I doubt it fries eggs....

Click to expand...

Google this search term: "Plant Available Nitrogen"

And you will be blessed with more PAN knowledge than you need/want. Imo, understanding PAN and timing of it's release is incredibly important for us that use organic inputs; else you are flying blind and "flushing" money down the drain (lol, pun intended).

So... basically my conclusion comes down to this:

Nitrogen leaching is practiced to rid the plant of chlorophyll.
But chlorophyll exists not only in the leaves, but in the buds as well. Chlorophyll exists wherever there is green, sometimes even where there is no green.
In other words, buds are full of chlorophyll. However, the chlorophyll breaks down during the drying and curing process, bringing out the desired flavors and aromas. Therefore, what is the point of nitrogen leaching to avoid chlorophyll when the buds are loaded with chlorophyll anyway? The answer is simple... it's not only pointless, but bad for the plant in general. Think about it, the plant leaches the nitrogen because it needs the nitrogen. And guess where the nitrogen in the leaves is going... straight to the buds! Most are unaware that nitrogen plays a key role in terpene synthesis, and it's the terpenes us connoisseurs are after!

From my experience, the best yields and flavors have come from plants that stayed lush green all the way to harvest. Of course this did not happen without a long and cold dry/cure. Nitrogen leaching is widely misunderstood, and has only brought me inferior results in both yield and potency. Can anyone else agree?

Has anyone else experienced better results with plants that were not malnourished in the final days of flowering?

Why don't you feed one plant until harvest day and flush
another plant two weeks before like what most people.

Then you tell us which smokes and tastes better.

If you have a media with any cec at all can you flush those off with water...nope.

Yesterday i saw a thread calles (don't) flush......... (i don't remember the name) and there were a lot of people/posts speaking about flushing.. when i find it i will post it here by editing this post

Feeding full nitrogen through to the flush is not "natural". Tests have shown that as the temperature changes with the season, so does the Ph of the soil. This alone can cause a reduction of the available nitrogen to the plant while still allowing good uptake of other nutrients.

You want to mimic nature? Skip it and grow organic outdoors. You grow indoors? You make the absolute best of the situation you can.

A plant feeding on nitrogen is completely "natural." Growing indoors, i lower the temps between 60-68 degrees towards the end of flowering. Sure the temperature may affect the pH, changing the ratios of nutrient uptakes, but there should still be enough nitrogen in the soil for the plant to feed on until harvest. If the plant is eating it, then it obviously needs it. A lack of nitrogen in the soil has nothing to do with pH. The pH will fluctuate, but the plant will always feed on nitrogen, no matter what. It is an essential nutrient for biosynthesis.

Also keep in mind that nature is the archetype upon which indoor growers base their environment. But nature does not always provide the best conditions for premium quality bud, and so we tweak the environmental conditions to optimize each individual strain. While quantity is easily achieved outdoors, in nature, conditions do not always favor quality. This is where indoor growing proves to be superior, especially for medicinal applications. Don't get me wrong, outdoor is still bomb when done right, but we get to use our intelligence and advanced knowledge of plants to modify indoor growing environments to stimulate cannabinoid production. Nature does not act in such a selective manner. Plants outdoors are forced to adapt or die. Indoors, we can discover the full potential of our favorite strains without interruptions such as rain storms, wind storms, heat waves, frost, high humidity, etc. Outdoor growers are not in control and therefore do not need much expertise. Indoor growers are fully responsible for their results, and this is where real experience and knowledge of plants is put to the test.

I prefer flowers that had a period of water prior to harvest. With chems it's necessary or you get beaster quality.

It's a fact that high nutrient levels damage resin. Outdoors here it rains last weeks before harvest. Until leaf falls nutrient levels go down.

It's truly a matter of preference and growing style. Timing and technique is everything.

FLUSHING is done to the medium in an effort to lower the available nutrients to the plant (ideally to zero) so that the plant can then LEACH (use up) the nutrients it has stored in reserves in the leaf and plant tissues.

Flushing can be done in stages or at once so the plants can leach themselves of nutrients for the 2 or more weeks prior to being cut down.

Also once cut 7-10 days at 60 degrees with 60% humidity is the rule of thumb...the cooler the room the denser the nugs will dry too, relative to their structure that is

Properly doing this your buds will burn to a wispy white ash and not all black and chunky (gross)


This process is not natural...neither is smoking.....but if you want your smoke smooth and dank you have to modify nature.....but hey, some people like their weed to taste like natural green grass clippings.....its their choice.

I would suggest people don't understand cec if they think you can flush cations off those sites with water...pure hydro ok, lightweight media, not a chance

jidoka said:

I would suggest people don't understand cec if they think you can flush cations off those sites with water...pure hydro ok, lightweight media, not a chance

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Like I said before. The old method of flushing prior to harvest wasn't to wash the medium. It was to give strait water so the nutrient levels get diluted as the plant takes up remaining nutrients. It's not going to occur with minerals as those are always being available.

If I take a cup of strong coffee and add a gallon of water. It's not going to be strong coffee.

810FireFarm said:

FLUSHING is done to the medium in an effort to lower the available nutrients to the plant (ideally to zero) so that the plant can then LEACH (use up) the nutrients it has stored in reserves in the leaf and plant tissues.

Flushing can be done in stages or at once so the plants can leach themselves of nutrients for the 2 or more weeks prior to being cut down.

Also once cut 7-10 days at 60 degrees with 60% humidity is the rule of thumb...the cooler the room the denser the nugs will dry too, relative to their structure that is

Properly doing this your buds will burn to a wispy white ash and not all black and chunky (gross)


This process is not natural...neither is smoking.....but if you want your smoke smooth and dank you have to modify nature.....but hey, some people like their weed to taste like natural green grass clippings.....its their choice.

Click to expand...

So please explain how giving the plant the nutrition it needs will lead to "grassy" tasting bud. As i previously noted, the buds are loaded with chlorophyll. So you can't tell me flushing is to rid the plant of chlorophyll. And if you "flush" to get nutrients out of the buds, what nutrients are you flushing and where are they going. In case you are not already aware, nutrients cannot be flushed out of the plant. The plant uses its nutrients for biosynthesis. In other words, the nutrients are being used by the plant for developmental processes. Starving the plant of an adequate nutrient supply will only inhibit these developmental processes. And keep in mind that cannabinoids develop more in the last week of flowering than any other phase.

That said, what are you trying to achieve by flushing exactly? Other than to rid the soil of excess solubles, what is the purpose of flushing?

The process of flushing was really for hydro guys using rockwool. It was more of a method to reset the medium and ensure control of the nutrient ratios available.
Nitrogen leaching, in theory, should be a natural part of overall nutrient control regardless of the medium used.
Personally, I like to see the larger fan leaves yellowed and bud leaves about to start at the point of harvest. Starving plants tends to reduce the sparkle level and not starving them leaves a natural green taste in the bud which I hate. So like so much, its a matter of finding the balance point you're happy with.