Flushing Indoor Grown Cannabis Plants
Not A Standardized Method
No studies have been published to date that examine the exact process of flushing cannabis plants.
However, this does not mean it is not common practice as the idea is to produce a high quality bud and also minimize inputs.
Goal of Any Flushing Protocol…
The goal is to reduce nutrient concentrations in the root zone so the plant metabolizes what is already present in the plant tissue.
Ideally water should be around room temperature (70-75F) and have a slightly acidic pH value 6.0-6.3 to aid in the ability to ensure nutrients are soluble and easily removed via the water.
First Nutrient to Go…
Nitrogen is the most water soluble of the nutrients so watch for a potential deficiency of this nutrient first in the plant.
This is characterized by yellowing of lower leaves while the upper portions of the plant remain green (at least for a period of time).
If you start to see this you may be flushing to early and aggressively.
Timing is Important
The goal is to time the reduction in nutrients with the harvesting of the buds.
When the plant runs out of nutrients this should be very close to harvesting so there is no plant stunting and chance at yield reduction.
Note: This is best done if you are going to be harvesting the entire plant and not selective bud harvest as this may result in the second harvest to be negatively impacted by the reduction in plant available nutrients.
Indoor Substrate Categories
This requires the least amount of time between stopping nutrients and harvest.
The exact type used can impact the timing.
Pure Hydroponic Production and Flushing
If a type of essentially substrate free system is being used (such as aeroponics, deep water culture) the roots will immediately loose access to nutrients once you add in only plain water.
So as a result you should only be running the plants with no nutrients for a 3-4 day flush period.
Otherwise the risk of nutrient deficiencies are increased.
Hydronic Substrate Based Flushing Recommendations
When plants are grown in a substrate there will be some retention of nutrients, but this will be in part substrate dependent.
Example if you are growing in clay pebbles or other material that requires near continual irrigation the 3-4 day recommendation for the hydroponic environment can be followed.
If you are growing in a peat moss or coco based substrate the duration of time of flushing can be increased to 4-7 days.
If using soilless mix it can get more complicated, simply because of the variability of components that exists with this category. However, in general this will be the longest interval and should be in the 5-8 day period of time.
Note: Also based on how aggressively you have fed during the end of the flowering phase will also impact how concentrated the substrate will likely be.
Basic Flushing Protocol…
Pure hydroponic set-up = Simple change the water with new water that does not contain any nutrients, but is pH appropriate.
Hydronic Substrate = Irrigate as you normally would with only water (no nutrients added), which should be until water come out of the container. This water leaving the root zone should be tested for EC or ppm or TDS. The goal is to increase the duration of irrigation until the readings are reduced to near plain irrigation water levels.
This will ensure the root zone has been flushed.
Link to Lecture Slides: https://drive.google.com/file/d/1GklN_RmH95RXJZl0uzxo1LyjJaF-KwnW/view?usp=sharing
*Due to the description character limit the full work cited for “Flushing Indoor Grown Cannabis Plants” can be viewed at… https://drive.google.com/file/d/1DF65lvcMqKux4DtaWW4A69DVYICdLNPl/view?usp=sharing
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