What is marijuana flushing and why is it important?

Unless you are growing your cannabis plants organically most growers will use a variety of different nutrients to aid the plants growth. While these nutrients are perfectly fine for a plant to absorb, if they are not flushed out of the plant before you put it in your joint, you will get a smoke that is both bitter tasting and harsh on the lungs and could be full of harmful nutrients. Flushing cannabis is the simple process of removing these nutrients out of the plants system by just watering them with fresh nutrient free water. 

Now that you understand the importance of the flushing process, you need to learn how to flush marijuana plants.

How long do I need to flush cannabis for?

Flushing cannabis in Soil

Soil tends to be very good at absorbing and holding onto nutrients so you will need to flush your plants for 1-2 weeks to do a thorough job.

Flushing cannabis in Coco Coir

Coco Coir doesn’t absorb and hold onto nutrients in the same way that soil does so flushing is a little quicker and should be done for 3 – 7 days.

Flushing cannabis in hydroponics

Hydroponics grows are the easiest to flush because the system can be completely drained of nutrients and water. You should still flush hydroponic grows for 2-4 days.

How to flush cannabis

Flushing your cannabis plants is probably the easiest stage of growing cannabis because that is required is access to clean untreated tap water, a bucket or watering can, some pH treatment.

  1. Wait until your plant is around two weeks away from harvest.
  2. Whenever you would typically feed your cannabis plants just do the same but with untreated nutrient free tap water.
  3. Before you begin flushing check the pH of the water using a pH meter – The ideal pH for growing cannabis is 6.0 – 6.5 for soil or 5.5 – 6.5 for hydroponic growing.
  4. If the pH of the water is too high or low treat the water gradually until you reach the required level.
  5. Once the water is at your desired pH level its time to begin. Start flushing by following your normal feeding schedule, use the same amount of water and just simply pour your nutrient free, pH tested water onto the soil.
  6. Continue this for around two weeks.

When to flush cannabis plants

The flushing process should be started around two weeks before the plants are harvested. You should read the breeder or seedbank guide on that particular strain to find out how long the flowering period is. If your plant has a flowering period of 10 weeks, then flushing can begin in around week 8. However please bear in mind that breeders often give the lowest possible flowering times on their website to appeal to growers wanting quick results, so I would probably add 1-2 weeks to this.

So that you are not flushing too early, another indication that the plant is almost ready to be harvested is that the trichomes will be just beginning to turn from clear to turn from clear to cloudy/milky, at this point you know that you have roughly 1-2 weeks until they have changed to milky/amber which is normally desired for harvesting.

Flushing marijuana too early

A common mistake that growers often make is flushing their plants too early. By flushing your plants too early you will stunt their growth because they will not be given enough nutrients in the final stages where the buds are really packing on size. You will also greatly reduce the quality of the weed produce because the buds will not have time to fully mature before harvest, meaning that your long awaited buds may not be quite as potent or tasty.

To avoid flushing your plants too early follow the rules above on when to flush your plants. The most accurate way is to check that the trichomes are beginning to turn cloudy/milky, you know then that your plant has around two weeks left until it is ready to harvest and so is ready to be flushed.

How do you know when flushing is complete?

Flushing should take two weeks, although in some circumstances you may want to cut it a few days short, anything from 1-2 weeks will be okay. When you flush your cannabis plants it is common for the leaves to begin to turn yellow, don’t worry this is normal when the plant is nearing its harvest period. However, you may want to harvest the plant before the small sugar leaves on the bud turn yellow. Although this does not necessarily affect the quality of the buds, it does affect the appearance.

After the flushing period you will notice that the plant and leaves will have changed to a much lighter shade of green, indicating that your buds are finally be ready to harvest.

How to flush cannabis in hydroponic grows

The advantage of growing hydroponically is that your roots are not surrounded by nutrient rich soil but by pebbles or whatever hydro medium you are using to grow with. Because hydro growing mediums do not absorb and hold nutrients as well as soil it is much easier and quicker to flush them.

To flush a hydroponics grow it is much quicker and easier:

  1. Start by emptying the reservoir and draining the system, then fill it back up again with fresh nutrient free water.
  2. Test the pH of the water and adjust it accordingly with solution.
  3. Begin flushing by turning your pumps on again and allowing the hydro system to do its job.
  4. Because hydro systems don’t absorb water and nutrients like soil you will only need to flush the plants for 2-4 days.

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