Flushing Cannabis: Why It’s So Important

Beautiful flushed cannabis flower, with yellow pistils

At one stage or another, when growing hydroponic cannabis, you will need to flush.

Flushing does two things. It’s clears the medium of built up nutrients, and aids the health of the plant by letting it use up excess nutrients (too much nutrient in a plant is the number one failure of amateur growing). Even if you are using Aeroponics, flushing is still important. In fact, in the final stages of the plant before harvest, it is crucial that flushing occurs just prior.

First and foremost, if you are using a non-aeroponic setup, such as ebb and flow, a good clean flush will rid the medium of concentrated nutrient which occurs due to evaporation. This can take from 1 day to a whole week, depending on the medium used, the air flow in the grow space, and how frequently you replace the water.

Flushed cannabis buds taste better

With an aeroponic system, the best practice is to remove the plants (for a very short period - max 10 minutes), and spray and drain the vessel with tap water. After replacing the plants, use tap water to spray the root system for about an hour.

Flushing should occur at least once per month for all of the above grow methods. Don’t worry; when done properly it will not hurt your product.

Harvest Flush

Finally, when time to harvest is estimated to be approximately 1 week into the future, replace the nutrient water with de-ionised water. This is the same type of water used in car batteries and clothing irons. If you are self growing, this can be obtained from your local supermarket. Using this water may turn the plant into a pale green colour. That’s right - your plant will technically become “ill” not just from the lack of nutrients, but will also somewhat strip the plant of phytochemicals as this means it is using them all up. This will ensure a product which turns quite pale, while the essential oil products (namely the trichomes) become prominent. The product will have more of a "classic flavour" and cure and smoke well.

This is a section from our harvest phase of the grow guide. Please also see our glossary of cannabis terms used in Australia.