Flushing cannabis plants prior to harvest is always been very controversial topic to many growers but flushing for other reasons is well mastered practice. So is flushing really necessary and when to perform it? And are unflushed autoflowers harsher and will not burn or burn with black ash?

Before flushing any plant we need to know what this flushing really accomplishes and how to do it properly!

What is flushing?

Flushing basically is the action when you pure a large amount of water through the growing medium, but it can also refer to the time when the plant is fed only with pure water for some period of time.

Why flush?

Flushing basically gets rid of the chemicals and built up salts from the growing medium and stresses the plant to start using its own chemicals from leafs and stems. In the wild cannabis plants will eventually “flush” themselves when autumn comes and they are almost done flowering – they start using their own nutrients to swell up the buds and mature the seeds that are in them. Of course they can’t flush the chemicals away from the ground but the rain helps a little and the plant just stops absorbing when it is almost ready for harvest. So if in nature cannabis plants flush themselves, why do we need to flush them if we are growing them indoors in controlled environment? There is multiple explanations why we need to flush autoflowers but they all are almost the same.

  • The most important aspect of flushing is to get rid of unwanted chemicals both in growing medium and also in the plant itself. If we want the smoke to be smooth and tasteful then we need to get rid of chemicals that are in the plants leafs and flushing the plant before harvest forces it to look for food in those leafs. And then your day neutral cannabis plant will use up these unwanted chemicals like Chlorophyll, magnesium , Nitrogen and phosphorus. Flushing is most useful if we grow our plants with chemical fertilizers because water binds together with these chemicals and easily flushes them away and the rest is up to the plant itself. But when we grow organically then flushing is also necessary, because there can also be some salts or chemicals in the ground and they most defiantly are in the plant so flushing again proves useful and we will get healthier and tastier smoke.
  • Another use for flushing is to get rid of excess nutrients and chemicals in the growing medium when the plant is still growing. Usually inexperienced growers feed the autoflower cannabis plant with far more nutrients than it can absorb and they build up in the ground and a good flush can wash all of those away.
  • One more useful thing about flushing is that by doing it you can fully wet your soil and there won’t be any more dry spots remaining in the middle of your growing medium. This is usually done before planting autoflowering cannabis seeds and is usually a standard procedure.

When Cannabis is flushed indoors or flushes itself outdoors at first we can see the big fan leafs to start yellowing and curling, and later also the smaller leafs start doing that, but that is all natural and the plants is just using up the food that is stored in those leafs.

How to?

When we want to just get rid of the excess salts or nutrients in the ground we need to flush 2 or 3 times the volume of the pot through the growing medium and let it leach out at the bottom with all those unnecessary elements and salts.

When the plant is flowering and it will soon be ready for harvest then we need to flush both the chemicals and nutrients in the ground and also let the plant use up its own salts, chemicals and nutrients. We need to time this process just right because too long flushing period can stress the plant and it can yield less. The flush must be done 5 to 10 days from the harvest and again it has to be 2 to 3 times the pot volume of PH adjusted water. When the first initial flush is done in those remaining days till the harvest you need to feed your autoflower plant only with pure PH adjusted water and the cannabis plant will use up it’s stored nutrients and your harvest will be healthier and amazingly tasty.

The third place where you need to use flushing is to prepare soil for seedlings. You need to flush at least 2 to 3 times the amount of pot with water so that every last peace of dry soil is wet and ready to nurture your autoflower roots.



  1. terry mckibbins on

    Finally clear and understandable info. on how why and when to flush thank you!

  2. Ken tchell on

    I cant believe you claim that Chlorophyl, magnesium, Nitrogen and phosphorus are unwanted chemicals! the Nitrogen, phosphorus and magnesium are absolutely essential for plant growth and metabolisim! The Chlorophyl is of course a major part of the plants metabolisim/catabolisim and necessary for the plant to survive!! It is for inaccurate, non-scientific explanatios like this and also just plain common sense that I do not believe in flushing! Its a waste of time and doesnt have any basis in science or plant physiology!

    • midowo

      I do not state that they are completely unwanted, but if they are in too high concentration they can have damaging effects and that is when you would flush them.

  3. this ken guy, f****** idiot thinking he knows what hes talking about. the nutrients were discussed as being negative in both the smoking and over fertilizing sense. f*** me some people.

    • banga j: totally agree.
      keyboard warriors everywhere!
      Great grow guide- very clear – very informative.

  4. I am in my last week of life cycle. Yesterday I started to use ripen instead of flushing them. Today I saw I have a problem with spider mites. Im afraid that that they will suck out the life of my beautiful buds, so I stated to think to either cute them and flush them.

    I don´t know if just cutting them without flush is good. I´ve used all so far Bio Grow and Bio Bloom (I stopped 2 weeks ago) so I don´t know if there is anything to be flushed. Im little confused because I saw there is a lot different opinions on this matter. If I grow in soil and use organic nuts do I need to flush or is flush more for hydroponics.

    • midowo

      If you have a spider mite problem I suggest you harvest your plants as soon as possible and don’t worry about flushing, as it is not that important. Those tiny creatures will otherwise ruin your crop!

  5. Juwanaman on

    It’s 2016 and this guide is still informative and relative. Guess who just flushed?

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