Flushing cannabis is a term that describes watering your plants without any nutrients to remove, or flush out, nutrient buildup from the roots of your plants and the surrounding soil. Flushing is typically performed for the last 7 to 10 days right before harvest and allows your plants to absorb the nutrients that are still in the soil and flushes out remaining nutrients and minerals to improve the quality of the end product. Flushing cannabis prior to harvest is performed mainly to avoid an unsatisfying, harsh end product and is thought to improve smokeability.

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When to Flush Cannabis Plants

Flushing cannabis is a good idea and is often performed for a few different reasons. The top three reasons and times that you should flush cannabis include:

  • 7 to 14 days prior to harvest
  • When incorporating a sudden change in the nutrient cycle
  • If your plants experience nutrient lockout

Flushing cannabis preharvest – preharvest flushing forces cannabis plants to use all their stored nutrients and improves smoothness and quality by removing built-up nutrients and excess chlorophyll. Preharvest flushing should be performed about 7 to 10 days prior to harvesting and should be repeated once a few days after the first flushing.

Nutrient cycle changes – cannabis plants progress through different growth stages, which require a different ratio of nutrients. Flushing cannabis is a good way to cleanse old nutrients when plants are transitioning into a new growth stage.

Nutrient lockout – when growers overfeed their plants with nutrients, excess nutrients can build up and cause a nutrient lockout. Getting too much of one nutrient could cause deficiencies in another and cause a plant to become unbalanced. Flushing cannabis at this time can correct any drastic changes you might see when there are no other issues such as root rot or problems with heating or light. Flushing can restore the pH balance in your soil to allow all nutrients to be absorbed properly. Using a pre-mixed nutrient solution can help prevent the delivery of one nutrient in excess while causing a deficiency in another.

How to Flush Cannabis

Flushing cannabis should not be performed too often or too early prior to harvest, or it could restrict needed nutrients and affect the plant’s growth and flowering stage. Generally, flushing occurs 7 to 14 days prior to harvest, with each grower developing their own method based on experience and knowledge.

  1. The first thing to do is to test the pH level of the water you will use for flushing to make sure that it has an acceptable pH range which should be between 6.0 to 6.8 for plants grown in soil.
  2. You should then water your plants like you normally would, at the same watering times, just without any nutrients or supplements. Do not overwater your plants more than usual to prevent deficiencies.
  3. Water your plants again 15 minutes after the first watering, and remember to repeat in 3 days.
  4. Use a total dissolved solids (TDS) reader to measure the TDS value to determine the purity of the water runoff. Ideally, water draining from your plants should have a TDS rating close to the neutral water used for flushing.
  5. Watch your plants for excessive yellowing. Preharvest cannabis flushing may cause plants to lose color. Some yellowing is normal, although be sure to harvest before leaves on buds turn yellow. Buds will begin to deteriorate after all the leaves have yellowed. Your plants will be lighter in color after flushing when ready for harvesting.

Flushing cannabis removes excess nutrients, nutrient buildup and is thought to provide smoother, less harsh buds for smoking. An article published in 2019 at High Times, however, reported that a research study showed that more people preferred smoking weed that had not been flushed compared to flushed cannabis in a blind test. This could occur if growers are over-fertilizing in the first place, meaning flushing may not be as necessary when growers are careful to not overfeed their plants. The general consensus is still that cannabis flushing is a good idea, although as research continues to increase in the cannabis industry, it’s always a good idea to question why we continue to do things “the way they’ve always been done and for growers to develop their own method of caring for their plants throughout all growth stages up to harvest with the method that best suits their fancy.

When growing at home, you could try different variations of flushing some plants at 7 days, flushing some at 14, or not flushing any at all and see which you prefer. Remember, quality plants start with quality seeds, and you can find the finest in weed seeds online from Mosca Seeds.

Mosca Seeds is recognized internationally as a quality cannabis seed breeder, practicing the finest in cannabis seed genetics to deliver the best pot seeds available. We offer a wide selection of marijuana seed types in regular, feminized or autoflowers, as well as potent Indicas, satisfying Sativas, and exciting Hybrids. Check out our Seed Bank to get the best pot seeds online delivered straight to your door to enjoy home growing and perfecting your flushing cannabis technique.