New Research Shows Flushing Plants Before Harvest May Be Unnecessary

burnin1

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From High Times
New Research Shows Flushing Plants Before Harvest May Be Unnecessary
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In a blind taste test, researchers have found that many prefer cannabis that has not been flushed before harvest.
November 28, 2019
By A.J. Herrington
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.

https://hightimes.com/grow/new-research-shows-flushing-plants-before-harvest-may-be-unnecessary/
 

oldfogey8

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Sounds like the research showed that you are throwing money away if you provide nutes up thru harvest since yield, potency and terpene profiles are not significantly different from flowers not fed the last couple weeks, right? Of course the nute manufacturer is going to focus on on people preferring the taste. Maybe the people they tested it on were used to smoking unflushed weed so that is what they prefer. Why feed them if you get really no benefit from feeding?
 

fellowsped

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Flushing has it's place. Nutrient lockouts, correcting the ph of your medium, and trying to flush excess salts out to keep them from plugging up the plants ability to intake nutes. However I don't think flushing in the last couple weeks is truly needed. Only thing I could think it would be useful for at the end is trying to flush mag out of the plant to keep buds from crackling. But there is an easier solution which is just don't over feed them towards the end.
 
K

Keef

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Another question -- Water pharmer !-- U want me to drain and refill my aero boxes so they can run the last few days-- without nutes just to flush them ?-- Sounds like a waste of time to me !-- Same nute solution from the beginning of bloom until the chop !-- Live res !--One res change half way thru !-- I can see where dirt or other medium might need to be flushed but I don't think it applies to me ?-- Seems to me shocking them with an environmental change right as they finishing up would be counterproductive .
 

St_Nick

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I'm all about the dirt. I feed nothing out of a bottle but I feed teas weekly and I feed to the end. I'll feed on a Wed. and harvest on Thurs. Done it many times. I do quit foliar feeding in the last couple of weeks.
 

JimmyNugs

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Am a newish grower but the idea that water into the root zone will take excess nutes out of the plant always seemed bonkers to me.

So many threads, so many angry people.

Flushing definitely has its place, but it isn't a magic liquid, it can't enter the plant, undo some growth then make a hasty exit with 'nutrients' .

It dissolves salt build (usually from non organic nutrients lines), it flushes and stabilizes the ph and it's good for washing an excess 'anything' in your medium away.

I have soil and coco grows and do a flush in coco every two weeks to make sure i don't have any related calmag issues, closely followed by a hearty feed (biobiz)

As for soil, well i run a flush when i used a traditional (pharm) PK product but stopped using as its non organic, so now i feed nutes up to cull in soil.

Nothing harsh goes into my weed now that would need flushing, not that flushing would make a difference anyhow.
 

Lesso

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Flushing has it's place. Nutrient lockouts, correcting the ph of your medium, and trying to flush excess salts out to keep them from plugging up the plants ability to intake nutes. However I don't think flushing in the last couple weeks is truly needed. Only thing I could think it would be useful for at the end is trying to flush mag out of the plant to keep buds from crackling. But there is an easier solution which is just don't over feed them towards the end.
It doesnt change the amount of magnesium at the end.
 

Lesso

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Sounds like the research showed that you are throwing money away if you provide nutes up thru harvest since yield, potency and terpene profiles are not significantly different from flowers not fed the last couple weeks, right? Of course the nute manufacturer is going to focus on on people preferring the taste. Maybe the people they tested it on were used to smoking unflushed weed so that is what they prefer. Why feed them if you get really no benefit from feeding?
Seems like this is the best argument for flushing, that there was no yield increase when using nutes all the way through.
 

fellowsped

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How does it have no effect on the mag in the end? Just seems like pumping a bunch of mag into your plant right before harvest would result in more in the final product. Isn't that what the crackling or sizzling is that you sometimes get? Could be wrong that's just what I had been brought to believe.
 
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