Learning how to flush marijuana is a critical step to produce top quality cannabis. The best way to flush marijuana plants is to use lots of plain, PH’d water for 10-14 days prior to harvest.
Properly flushing your plants with plain water helps weed plants consume much of the residual nutrients that are in it. This will greatly improve the overall quality of your cannabis buds. Improperly flushed marijuana will not taste as good or burn as well.
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 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 such as 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 time accordingly.
How much water should you use to flush cannabis plants?
You should use enough water to roughly triple the container size to properly flush weed plants. 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.
It is a good idea to use about half this 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. The pH of water used for flushing is similar to the range you use for normal waterings. This would be 5.8 – 6.0 for coco coir, 5.5 – 6.0 for hydro, and 6 – 6.5 for soil.
If you are growing 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.
Some growers connect their plants to automated watering pumps or even putting it in the bath tub and run the water through the shower. This makes it easy but will add chlorine and it wont 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 try to pH down many batches in 5 gallon buckets.
For a small home grow, I prefer to fill a 30 gallon plastic barrel with water, adjust the ph down to 5.8 – 6.0, and then use an automated watering system with watering rings to slowly dump that water on the plants.
How can you tell if weed plants are properly flushed?
The best way to tell if cannabis plants are properly flushed is to monitor the run off water from 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.
If you growing hydroponically, flushing affects your plants quicker than if in soil since the roots are directly in water. Some hydro growers will gradually lower the water’s PPM for a few days to avoid shocking the plants.
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 plants event better than pure water.
I’ve never done a side by side test so I can’t attest to this. Most growers I 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.