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.
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 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.
Multiple flushing cycles 2 days apart will really clear out nutrient salts from your coco medium.
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.
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.
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.
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.
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.
Learn how to flush marijuana plants to produce top quality cannabis. Use plain, pH'd water 10-14 days prior to harvest, watering 3-5x your container size.
When looking to perform a flush before harvest, there are more factors to consider. Make sure your plants will be ready for harvest once the flush is complete. Flushing too early or too late will result in a lower-quality product.
Once again, 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.
Trevor is a freelance writer and photographer. He has spent years in California working in the cannabis industry.
Flushing your plants will remove excess buildup of salts and nutrients while helping to restore the soil’s pH balance. This will allow your garden to resume absorbing nutrients and grow at a healthy, successful rate.
Different growing mediums require different flushing time frames before harvest:
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.
Think of it as someone changing their diet. You can fill your fridge with new types of food, but you might find yourself running out of room if you never removed the old food. By removing the old food, you are clearing a path and starting anew.
Cannabis plants have different nutrient needs throughout different stages of growth; what it needs in its vegetative stage is different than what it needs while flowering. Clearing old nutrients during the transition into the new stage of growth will help kickstart the plant’s journey into flowering.
- Soil: 2 weeks
- Rockwool and coco: 1 week
- Hydroponics: 1 week or less
Flushing is when you stop feeding your cannabis plants nutrients and give them water. The process is generally as easy at it sounds, but it's crucial to know precisely when and how often to flush.