When And How To Flush Your Cannabis Plants

Flushing is so important to cannabis cultivation. Some problems can be corrected with a flush, and a pre-harvest flush will unlock all the flavour of the flowers. This is your essential guide to flushing cannabis.

Flushing Cannabis


Flushing is simply the process of drenching the growing medium with pure water or flushing solution. Whether you grow organic, hydroponic or somewhere in-between, you will need to flush your cannabis plants. The purpose of flushing is to get the plant to absorb the remaining nutrients in the soil and/or leach-off excess nutrients.

Of course, this depends on when and why you are flushing in the first place. Later, we will break this down. Typically, aside from the final pre-harvest flush, most cannabis cultivators will only flush when plants are showing signs of nutrient lockout or over-fertilisation.


How To Flush Cannabis Plants

No special tools or techniques are required to flush cannabis plants. Instead of feeding plants nutrient solution, the grower simply feeds pure water or a light flushing solution. If you water by hand, then you can flush by hand. Similarly, if you use an automatic watering system, you can fill her up with pure water or flushing solution instead of the usual cocktail of nutes.

The most important factor is to thoroughly drench the medium. A good rule of thumb is to apply double the normal feed volume of water. Just make sure you don’t leave the plant’s roots sitting in a puddle of runoff water afterwards.

When To Flush?

When To Flush?

The three situations where it’s appropriate to flush your cannabis plants are as follows:


Some growers like to give their cannabis plants a flush as they progress through their lifecycle. This is most common when making the switch from vegetative growth to the bloom phase. As the plant's nutrient needs change, it’s no harm to flush in order to prevent a build-up of nutes from the previous stage. This kind of flushing is not essential, but is recommended for a smoother transition.


If your marijuana is looking unhealthy and displaying the warning signs of nutrient lockout, it’s time to flush. Yellowing leaves, stunted growth, and overall lack of vigour are telltale signs of some kind of nutrient lockout. To remedy the situation, it’s always best to start with a flush before tinkering and adjusting nutrient doses. Flush, monitor behaviour, then start tweaking the fertiliser ratios.

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Learn How, When And Why To Feed Your Cannabis Plants Nutrients


Even if you feed your cannabis plants very light doses of organic nutrients, you still need to perform a pre-harvest flush. Those who believe organic nutes don’t taint the finished product with a fertiliser flavour are sorely mistaken. All fertilisers effect flavour, albeit to varying degrees. Nutrients will accumulate in the medium over time one way or another.

At the very least, most growers will apply high doses of bloom boosters to increase yield. Whatever feed goes in during the cannabis lifecycle must be rinsed out before you give plants the chop. If you feed marijuana high doses of nutrients and supplements, then you must flush them out thoroughly before harvesting.

If you are using an organic soil that has been pre-fertilised specifically for cannabis plants, you probably should only flush prior to harvest. Regularly flushing this kind of medium will wash out all the time-released nutrients that enrich the soil. Flooding your super-soil with water defeats the purpose of using it to begin with.


The Importance Of The Final Flush

The pre-harvest flush or final flush is the last step of the grow cycle. Soil growers need to allow two weeks before harvest day to flush, while coco and hydro growers can cut this down to just one week. Flowers must be inspected to ensure they are ripe and ready. Flush too soon and you will have cleansed an immature bud stash. Flush with too little water or not frequently enough and nutrient salts won’t wash out.

Soil growers need to use water with a pH value of 6.0, while 5.8 is best for coco and hydroponics. Should the pH be too high or too low, the flush won’t work. Watering needs to be dialled-in to suit the medium.

Use an EC meter to accurately gauge the progressive reduction in ppm from the runoff post-flushing. Alternatively, eyeball inspect the runoff for discolouration. Ideally, the water should run clear and contain little total dissolved solids (TDS).


Flushing By Hand Vs Flushing A System

Flushing by hand is simple and effective. That’s fine for the organic home grower with a handful of plants. However, hydroponics relies mostly on automatic watering systems. Nonetheless, the same principles apply. The reservoir is typically filled with a light flushing solution that runs through just like a nutrient solution.

Chemical fertilisers are responsible for the common hydro bud’s lack of flavour. Pure water just doesn’t cut it the way it does with an organic soil grow. Double-down on watering with flushing solution for 5-7 days to unlock full flavour from those fat hydro buds. Don’t forget to check the runoff to make sure you are flushing out all the residual nutes.

Steven Voser
Steven Voser
Steven Voser is an independent cannabis journalist with over 6 years of experience writing about all things weed; how to grow it, how best to enjoy it, and the booming industry and murky legal landscape surrounding it.