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Flushing Cannabis Plants

By Last updated on April 3, 2023April 3rd, 2023No Comments

When it comes to harvesting your cannabis plants, many people think that the timing and the actual process of harvesting are all that matters. However, many other aspects also come into play. One of these aspects is flushing your weed plants before the harvest.

Flushing can be critical, and it is not too difficult to do. That being said, the timing can be tricky, and it can turn the result into something fantastic or something terrible.

Not properly flushing a plant can create a less than pleasant smoke. This is caused by the nutrients and minerals used during the growth process still being present in the plant, altering the way it burns. Flushing removes these remaining nutrients, improving the quality of the smoking experience.

What is flushing?

Flushing is the process of removing leftover nutrients from the soil of your cannabis plants with neutral water. Water is an incredibly powerful element, and it can do wonders for your plants beyond your simple feeding regiment. It can flush away leftover nutrients and minerals, allowing the soil and plants to be fresh again.

Taking away the minerals may sound like a negative thing to do at first, but in fact, it is an incredibly helpful process. Flushing out minerals paves the way for the roots of your plants to take in any remaining nutrients still in the soil.

Much like people or animals, it is a way of “starving” the plants so it absorbs any fat that was leftover and can be used for energy. The hard part is to time it right. You need to flush your cannabis plants at a short enough time before the harvest so that the plants do not have enough time to start becoming unhealthy.

When should I flush?

The best time to flush your plants is approximately 2 weeks before you plan on harvesting. However, this timing does not work perfectly for all weed strains and grow setups. In terms of timing the harvest itself, keep a close eye on the trichomes of your plants because they will clearly illustrate which plants are ready to be harvested.

Plants that have mostly clear trichomes and only a few that are milky and white are too early to harvest but are perfect for flushing. Two weeks after the big flush, you want most of the trichomes to have already changed color. This can be tricky, especially for new growers, but it is important to think about it nonetheless.

The timing also varies according to your grow medium and setup. For example, people who are growing their weed plants in amended soil should not flush at all, while people growing their plants in soil should flush them several weeks before the harvest. Coco growers should flush their plants about a week before harvest, while other hydroponics growers should only flush for a few days.

Flushing is not exclusive to harvest time. The technique can also be used in the vegetative phase to remove excess nutrients from the soil. Sure, nutrients keep your plant healthy and ensure optimal yields, but too much can cause nutrient lockout; a state where plants cannot access nutrients.

Nutrient lockout can be caused by both salt buildup and incorrect pH levels. It can be solved by flushing affected plants with plain water. The fluids push nutrients out of the soil and wash away the buildup, allowing roots to once again freely uptake nutrients.

How to flush cannabis plants

How to flush cannabis plants

Once again, flushing cannabis simply involves running pure water through the soil or medium. When trying to stop a nutrient lockout or when switching nutrients, perform a flush by excessively watering your plants with water that has a pH level between 5.5-6.5 (for hydroponics) or 6.0-6.8 (for soil). Fully saturate your pots, and repeat 15 minutes later. The flush should clear any blockage and make room for your new feeding schedule.

To be certain a flush was successful, you can use a TDS (total dissolved solids) reader to determine how pure the water runoff is. You want the TDS reading of the water draining out of the pot to be close to the TDS reading of the pure water you are flushing with. This reading will ensure that the nutrients have been washed out of the soil.

Different growing mediums require different flushing time frames before harvest:

  • Soil: 2 weeks
  • Rockwool and coco: 1 week
  • Hydroponics: 1 week or less

When not to flush cannabis plants

The only time flushing is not encouraged is when you are growing in amended organic soil. This is because your soil already holds all the nutrients the plants need to thrive. By flooding the soil, you can wash away and damage the complex ecosystem that you have worked so hard to develop in the soil itself.

Furthermore, these plants almost always receive pure water during waterings. The nutrient uptake by plants in this environment is natural, diverse, and easy for the plant to process.