Flushing weed: how to flush marijuana plants

Learning how to flush marijuana plants is a critical step to producing top quality cannabis. The best way to flush weed plants is to use lots of plain, PH’d water for 10-14 days prior to harvest using the steps outlined below.

Properly flushing marijuana plants with plain water removes available nutrients from the grow medium.  This forces weed plants consume nutrients it has already taken up and is storing in fan leaves.

Best time to flush marijuana plants

You need to make sure to plan and allow time to properly flush. Don’t let the harvest window sneak up on you.

If you are looking for a 14 days flush and you know you are running an 8 week flowering strain, the best time to flush weed with plain water is the start of week 7. This will allow for 2 full weeks. But also keep in mind that there are environmental stresses including excessive heat or insect damage that can extend the typical flowering time required for your plants, and if your plants are a bit behind you’ll need to adjust your flush start time accordingly.

How to flush marijuana plants in coco coir

To properly flush marijuana plants in coco coir you should use enough water to roughly triple the container size. For example if you are growing in 5 gallon smart pots, you would want to use 15 gallons of clean, properly pH’d water per plant.

Make sure to not water too quickly when flushing in smart pots, you want to let the water run through the coco rather than pour out the sides. Try using half the water on the plants, let it sit for 5 minutes, and then add the other half to ensure that you dissolve in remove as many nutrients salts as possible from your medium.  If you’re using a automated watering system set it on a slow setting.

When flushing marijuana plants the pH of the water is similar to the range you use for normal waterings. This would typically be 5.8 – 6.2 for coco coir, 5.5 – 6.0 for hydro, and 6 – 6.5 for soil.

Multiple flushing cycles 2 days apart will really clear out nutrient salts from your coco medium.

Flushing marijuana plants in soil

If you are flushing marijuana plants in soil, you will need to flush with about 3 to 5 times as much water as the container size you’re working with. So for a 5 gallon container, you would use between 15 to 25 gallons of water to flush. If you’re a light feeder, go with 3x. If you feed heavy (any burnt tips, that’s an easy way to tell) then go with 5x.  You can’t really overdo it.

Some growers connect their plants to automated watering pumps, using garden hoses, or running the water through the shower. This makes it easy, but will add chlorine and it won’t have a lowered pH, which isn’t ideal. But for growers with a lot of plants to flush using straight tap water is a much easier solution then to pH down many batches in buckets.

If you have a small home grow and are flushing marijuana plants in coco coir or soil, a 30-gallon plastic barrel filled with water comes in handy. Let it sit a day or two to dissipate the chlorine, adjust the ph down to 5.8 – 6.0, and then use an automated watering system or a hose on a strong pump to slowly release water on the plants.

How to flush marijuana plants in direct-water culture (DWC) or hydroponic growing systems

Flushing takes effect quickly when you grow cannabis hydroponically since the roots are in direct contact with the nutrient solution. Once you start providing plain, pH’d water the effect of flushing will begin.  Because of this you can start flushing 7 days before anticipated harvest. Some hydro growers will gradually lower the water’s PPM for a few days to avoid shocking the plants.

How can you tell if weed plants are properly flushed in coco?

The best way to tell if cannabis plants are properly flushed in coco coir is to monitor the run-off water escaping the bottom of the container. Your goal is to see PPM levels that are equivalent to the water you’re putting into it. If it seems higher than the plain water you started with, keep flushing.

If you over-fertilize your plants, you will find that you need to flush more then if you are a light feeder. Measuring the PPM’s of runoff throughout the grow cycle can help you understand this better.

Remember f you growing hydroponically, flushing affects your plants quicker than if in soil since the roots are directly in water.

If you over-flush your sugar leaves may yellow which affects final bud appearance, but the improvements in flavor, taste, and smokability will be well worth it. Cut those leaves at the stems when trimming and you’ll be fine. This can happen if your plants take longer to reach the harvest window due to a schedule miscalculation or problems in the flowering period that extend the flowering times for plants.

Are nutrient flushing and salt clearing products like FloraKleen and Clearex worth it?

General Hydroponics FloraKleen Mineral Salt Clearing Solution and Botanicare CLEAREX Rinsing Solution are salt leeching products designed to help leech excess nutrient salts from your plants. They are marketed as helping flush weed plants event better than pure water.

Having never done a side by side test we can’t attest to this. Most growers we know go with the plain water approach. But if you want to go the extra mile, or if the harvest window snuck up on you and you don’t have a full 2 weeks to flush then these nutrient mineral salt clearing or rinsing solutions can help you make up for lost time.

Summary: Flushing marijuana plants

Knowing how to flush marijuana plants comes down to a few key things:

  • Slowly flush with plenty of clean, pH’d down water
  • The amount of water per plant is 3-5x your container size
  • Begin flushing plants 10-14 days before harvest for grows in coco coir or soil.
Flushing weed: how to flush marijuana plants
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Flushing weed: how to flush marijuana plants
Learn how to flush your marijuana plants to produce top quality cannabis. The best way to flush weed plants is to use lots of plain, PH'd water for 10-14 days prior to harvest.
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Happy Pot Farmer
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