Posted on by Alex Russell

Flushing your plants

22/2/19 - This is an updated version to a previous tutorial on flushing.

Flushing is a technique used in between feeding weeks to ensure nutrition is available to the plant at all times, it is also used in the maturation (harvest) stage of a plants life. Flushing your plants before you harvest is crucial if you want your crop to be resinous, aromatic and full of flavour.

Flushing your pots or systems free of nutrients allows for both a fresh feeding schedule to resume or allows the plants to consume the remaining nutrients built up within itself. When it comes time to final harvest, if your plants haven’t been effectively 'cleaned', you will have built up nutrient and carbohydrates still within the plant, resulting in a much harsher crop that generally tastes like the nutrients you were plugging them with!

Some cleansing products are dedicated to this phase and specialised solutions actively seek out excess salts and convert them back into useable forms for the plant.


Timing is key with flushing.

Experienced growers understand the benefits of flushing weekly, this will result in a super healthy plant always consuming fresh nutrients.

Plants that go through life not ever being flushed will go through a myriad of problems only confusing the grower.

At A-Grade Hydroponics we recommend gardeners to flush regularly in hydroponics and coco based systems.

Think of an un-flushed plant as sitting in a bath that has not been changed for a few weeks, it may be sitting in toxic mineral build up.


Flushing Toxic Buildup (Mid-Grow Flushing)

A common issue but almost always mis-diagnosed that many hydroponic growers will run into during their first few grows, is a toxic build up and accumulation of mineral salts within their medium. This is rather common for growers that use coco mediums with hydroponic nutrients, allowing a slow creep up of medium EC and huge pH swing as a result, which can be devastating or even fatal to the plant if left unchecked.

Why do I need to flush mid-grow and how will I know when I need to?

For the best and most accurate results when growing using hydroponic nutrients, you should be measuring your run-off from your plants everyday, at minimum once every 3 days.

'Run-off' is the excess liquid that will run out of the bottom of your pot after a feed, measuring this liquid will give you a good idea of what the pH and EC is actually like in your medium. If you are feeding your plants a 1.5 EC, 6.0 pH solution and the run-off is measuring 2.1 EC and 5.3 pH, then your medium is likely in a toxic state to the plant and sitting in an acidic pH environment. This will cause nutrient lock-out and stunt growth, eventually killing the plant over time.

This has occurred because the grower has been feeding too many nutrients to the plant that it was unable to consume before the next feed happened, building up an excess of mineral salts (nutrients) in the medium.

To correct mineral salt build up in the medium, the answer is to flush the pot and medium using plain water to dilute and clean out all the accumulated minerals. To do this, simply flood the medium with plain water and measure the run off, repeating this process until you have a run-off reading in the range you are happy with.

In the case above, you are trying to feed 1.5 EC / 6.0 pH to your plant, but your run-off is reading 2.1 EC / 5.3 pH, you would want to flush your medium with plain water repeatedly until the flush run-off is reading a safe range, such as 0.5 EC / 5.8+ pH. This may take several flushes and lots of water to achieve. If you were to skip the flush and feed this toxic pot with your 1.5 EC / 6.0 pH solution, you would end up increasing the EC in the medium even further into toxic conditions and killing your plant at a faster rate.


The Final Flush (Harvest Flushing)

If you are reading this tutorial because you’re near the end of your flowering phase then follow these steps to ensure you’re not flushing too early.

  • Pay attention to the overall form of the flower and fruit, usually with an 8-week strain, the flowers development starts to plateau around week 6 - 6.5
  • At this time, we massively reduce our nutrient solution concentration.
  • Usually before this transition most growers would have an EC between 1.5-2.0
  • Remove any old solutions and replace with plain water, correcting the pH to 6.0-6.2
  • Most tap water in Australia is between 0.0-0.1 EC
  • Ideal maturation is 0.1-0.3 EC


Coco Flush:

The key here is to flood the pots until the water is running freely out of the base of the pot, you would then allow the plant to naturally dry up the pot itself, then its rinse and repeat for approx. 7-14 days.


Hydroponic Flush:

For systems where the roots are permanently sitting in nutrient solution, such as Deep Water Culture, the flush of these systems are the easiest and fastest, as no build up of nutrients can occur in the medium. Start by removing old nutrient solution from tub/reservoir and fill with plain water at pH 5.8-6.0, the plants would then sit in this water for around 7 days until harvest.

Alternatively, some growers prefer to scale down the nutrient solution strength over a two week period until the EC of their reservoirs reach around 0.5 for the final 3-5 days, simulating that of a downscaling coco flush.


A harvesting tip:

Harvest your plants before the lights are due to come on, this ensures there are no left-over nutrients being circulated through the veins of the plant, remember as soon as light touches them the capillary action re-commences.

Utilising this method will also ensure in maximum terpenoid profile, after a long day of light exposure the terpenoid hydrocarbons evaporate, by harvesting this way you will always have a super aromatic crop!