When and How to Flush Autoflower Cannabis Plants?

When the plant is flowering and it will soon be ready for harvest then we need to flush both the chemicals and nutrients in the ground and also let the plant use up its own salts, chemicals and nutrients. We need to time this process just right because too long flushing period can stress the plant and it can yield less.

Flushing can improve the quality of the buds, but only if it’s done right. Flushing is done under two conditions, and they are:

  • Just before harvest
  • During a nutrient lock-out



Plants are flushed a few weeks (at least 2 weeks) before harvest to remove any excess nutrients. For instance, if your plant has a flowering period of about 10 weeks, you can start flushing once it reaches 8 weeks. However, ensure that the plants are almost ready to be harvested before you flush them.

This means that you must check the trichomes or at least take the color of the buds into consideration. If the buds are almost amber with only a few white pistils in between, the plant is ready to be flushed. In case the buds are filled with only white pistils with no amber or red pistils, you will need to wait a bit more.

A Nutrient Lock-Out

The amount of nutrients you sometimes feed to your autoflowers can increase to such an extent that it results in a nutrient lock-out where the plant can no longer feed itself. This situation can be threatening to the plant and usually results in small yields. If the leaves look like they are burnt or are abnormally dark green in color, it’s a sign of a nutrient lock-out. Overfeeding can also result in nutrient lock-out. For example, excess nitrogen can result in nitrogen toxicity where the leaves begin to look like claws.

In such situations, it’s important to restore the plant back to normalcy. And, that can be done only by flushing. Flushing removes all the excess nutrients and allows the plant to grow normally. Of course, you cannot correct the problem immediately, but it takes at least 2-3 days for the plant to reset itself and get back to normalcy.

Remember that while flushing to remove excess chemicals is done during the vegetative stage, flushing to make the buds smoother is done during the final flowering stage. There’s a lot of difference between the two.

Flushing cannabis simply involves running pure water though 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.

Once you’ve properly flushed and harvested your garden, it’s important to dry and cure the cannabis correctly. It is through a quality flush and a long cure that your cannabis will be able to fully express itself.

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When looking to perform a flush before harvest, there are more factors to consider. Flushing your autos should be a planned event. Thus, time it well. What happens if you flush at the wrong time? You simply force the plant to get rid of its own food and render it helpless.

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