As a new (legal) cannabis grower, I’ve noticed a lot of people swear by “flushing” plants to remove toxins/nutrients and to provide a smoother smoke. Others say flushing is BS…and it sounds like it to me. What’s the straight dope on it?
Definition of flushing (credit: maximumyield.com): “Flushing is the technique of ceasing to provide nutrients to a cannabis plant and instead only applying water. The process of flushing the marijuana plant usually takes place during the final transition phase of the plant’s life right before harvest. Ceasing to provide additional nutrients forces the plant to utilize its stored nutrients during its final week of growth. If a marijuana plant has excessive nutrients stored in its plant material, the built-up nutrients can affect the flavor of the plant and its overall quality.”
It’s gonna depend a lot on what nutes you’re using but flushing will never hurt anything. If you’re using coco coir or soil there’s plenty of nutrients stockpiled in the medium and in the plant itself (in those big water leaves, mostly) to let it finish out with nothing but water the last week.
Well, if you keep fertilizing until the day of harvest, the resulting product burns down to a black charcoal like ash. If you stop fertilizing at a prudent time beforehand, the resulting product burns to a fine white ash. The latter provides a clearer signal when it’s “cashed”, preventing folks from burning the darker charcoal like ash in an attempt to not waste what they paid for, even though it’s pretty much just making them cough.
Fertilizing until the day of harvest will give you more yield, but honestly results in an inferior product. If your aim is to grow for smoke-able flowers, I’d personally advise on not fertilizing for a time before the harvest, the actual time that you would stop would depend on the medium you’re growing in.
Interesting…I recently bought some bulk cheap weed from a local store here in Canada and it burnt to a hard charcoal as you described…wasn’t sure if that was bad curing or something else.
I think that’s more of a curing thing than a flushing thing–I’ve grown with and without an ending flush with the same clones and it never really makes a difference, but poor curing and drying, that will be a big factor. Poor curing and too-fast drying lead to harshness too, as does a less than tight trim job.
Nah, that was almost assuredly fertilizing the plant to its limits and not giving it a break during the end of flowering. In my experience, the fertilizing controls a lot of things, but when you stop controls how well the end product actually burns.
An improper cure will usually result in odd flavors - usually minty flavors in an under cure and musty flavors in an over cure. In between, there’s a range of cures to be had. Since I grew up on decades of brick weed, I personally prefer the smoother smoke of a long cure, but that’s not the fashion these days. Bright and flavorful is the name of the game, and I understand it, even if it’s not the smoothest way to go.
For plants (as well as animals and humans), anytime you hear a claim about flushing out ‘‘toxins’’, you can be almost 100% sure that it’s total bull (an exception would be medically-indicated chelation therapy for known toxic metal exposures).
My gardening experience does not extend to dope growing, but claims like these require actual evidence.
SWIM used to grow some primo dope, and swore by flushing a week or so prior to harvest. This was in plants grown in a soil substitute and fed with nonorganic nute system.
Flushing and curing definitely has an effect on final product, but I think a bad cure has more obvious effects (hay smell).
Well my gardening experience does include dope growing and I agree with you. This Flushing is all bunk and needs some evidence. This was posted after all General Questions.
Plants will only uptake and use the nutrients that they need, the rest is left in the soil or other growing medium. The theory that they will continue to stuff themselves with unneeded whatever and that ends up in the product that you smoke is just woo. Thinking that the flowers are somehow getting too woody and will turn into lumps of charcoal when you burn it is misunderstanding basic plant biology. But there has been so much woo associated with marijuana cultivation that it remains an unfortunate problem. As this crop is moving into main stream production hopefully this sort of thing will fade away. Along with the ridiculous naming conventions which are not helpful and mean nothing.
Flushing with water to clear out “stuff” is not science. Unless maybe you have chronic kidney stones.
Now, if you will excuse me, I need to detox my liver with essential oils.
A little more. There is nothing special about a cannabis plant. It goes through the same stages as any annual flower. There is a seedling stage, a vegetative stage when growth is the goal, and a flowering or fruiting stage. You wait to fertilize until the seedling is established, fertilize and water during the growth/vegetative stage, and then leave it alone to flower or produce fruit. Maybe adding some bloom fertilizer late. If you have your soil/medium correct you won’t even need that.
This is correct. Flushing is a myth, as is much of the information surrounding cannabis cultivation and preparation. It’s an unfortunate consequence of abruptly going from illegal and popular to quasi-legal and incredibly lucrative. Anyone and everyone gets to be an authority in a space that science hasn’t yet really penetrated.
Heh, I didn’t even think this was really controversial. So, I checked Ed Rosenthal’s site. He just about covers it:
Obviously, I’m on the side of what he considers the consensus.
Yes, the plant will take up nutrients it cannot use. It will take up nutrients until it dies from it. Over fertilizing your plants will kill them pretty quick. But that’s not even the argument here. The argument is that the extra nutrients make the end product not as good to smoke. As of yet, I haven’t seen any evidence that this isn’t the case.
However, I went poking around and found this study (warning, PDF).
Missed the edit window, but this is partially incorrect. Over fertilizing normally just keeps the plant from being able to absorb water from the environment. It’s not normally from it taking up too much nutrients.
Well, I’ve learned something from this thread - mainly that cannabis growers are susceptible to the same sorts of dubious claims and questionable science that affect other specialty crop growers and generalist gardeners.*
The idea that over fertilization of herbs (including M.J. as an herb in the discussion) leads to lush nitrogen-fueled growth and lower concentrations of active/tasty ingredients potentially has merit (again, specific claims require solid evidence of altered concentrations of active substances, not “I swear it tastes/smokes better”). Stopping fertilizer a week before harvest doesn’t provide enough time for desirable chemical concentrations to build back up in the plants, nor would “flushing” steer overfertilized plants back to health in such a short period (i.e. reversing stunting or replacing fertilizer-burned foliage with healthy new growth).
For plants grown in coir-based soil/soilless mix, I’ve seen recommendations to “flush” out the media before using it to lower undesirable salt concentrations, though the coir I use hasn’t presented any problems in that regard.
*the array of wildly overpriced fertilizers, additives and fancy lighting setups in hydroponics stores is something to behold. One of the latest “growth” businesses involves “beneficial bacteria”. What they actually benefit in real-world applications is mostly guesswork at this point.
Well, I can attest that the use of Bacillus thurigensis israelensis does cut down on the likelihood of fungus gnats and the attendant flyers in an indoor environment. Growing indoors does present its own unique set of problems requiring sometimes very creative solutions because you don’t have a whole biosphere in there to keep things in check.
I agree on the silliness of the whole range of super duper overpriced nutrient “systems” out there–me, I use JR Peters Jack’s Pro inorganic salts, cheap, simple, absolutely foolproof if you know what the fuck you’re doing and aren’t one of those rash reactionary idiots who throws spaghetti at the wall every time there’s a perceived problem. I’ve given up arguing over nutes with people, it’s like a fucking religion to them and we all know how successful THAT is.