Have you ever coughed so hard after taking a hit that you feel like you were on the verge of bronchitis? Or what about smoking a joint and realizing you have a fertilizer taste in your mouth? This could be because you didn't flush your plants before harvest.
Flushing your marijuana plant is kind of like giving it a detox from all the nutrient salts and nourishing chemicals that may have been stored in your cannabis plant's tissues. Your plant stores these nutrients in its leaves in case they don't get fed again for a while. Since we're all good-loving plant parents and without fail (if you're smart, that is) continue to feed them, they don't need all the stored-up food. This is where our loving care comes in because they can't get rid of it without us. Your plant's growing medium, the soil, needs to get flushed to get rid of the excess nutrient buildup, and then, and only then, will your plant use up the stored nutrients when it's not fed more incoming nutrients. However important the fertilizers are, it is important to clean up after a few months at the diner-so to speak :) because this nutrient buildup is what causes your smoke to be harsh and bad tasting. Contaminated buds contaminate your health and high; you'll be smoking weed and whatever food it was given. Your poor lungs will suffer! Because the bud doesn't light properly, you lose sufficient combustion and full decarboxylation (when THCA converts to THC).
Smooth and tasty
After buying some bud you can tell if it's been flushed by lighting it up! If the joint is hard to light and the ash is dark, it's probably not been flushed. Your ash should be white-gray, and inhaling should be like it's meant to be, Mmmmh smooth and tasty.
You'll want to wait to start the flushing until it's the early end of the harvest window when you can practically harvest it already. It's a big mistake to start flushing too early as it stunts the growth because the buds are not getting the right amount of nutrients to develop properly. If it doesn't get the right amount of nutrients during the most critical parts of the flowering stage, you're putting the quality and potency at stake. If you're too hasty with starting the flush and realize afterward that your plants still need a couple of weeks to mature fully, then you have a situation on your hands. You would have to decide whether to harvest it early, continue to flush (which can cause nutrient deficiency) or go back to using nutrients.
Pump and drain
The entire flushing will take 2 weeks if you want it done thoroughly, but if you don't think you need to do it for so long, aim for at least 10 days. Let's first look at flushing when you are using soil as your medium. First off, put your pots in a draining tray to catch the runoff water. You can also place them in a large enough sink if you have one. Then, using pure water with a pH of 6.0 to 6.8 water your plants with a few gallons of water. Use a shop vac to suck up the water from the draining tray. Avoid letting your plant sit in the runoff water for too long as the nutrients can get leached in again and that will just, makings pointless.
The idea stays basically the same if you use a hydro setup. Unplug your water pump and drain all the water. After detaching the hoses from the bucket, sterilize your system. Now you can add the water back into the reservoir. Don't forget that your water should have a pH of between 5.5 and 6.5. Now you can reattach the hoses and let the water circulate for 2-3 hours. Next, you should repeat the process of draining your system and adding new water. Allow that water to circulate in your system until the following day. Replace the water again for the 3rd time and keep this water circulating for the next 10-14 days. Keep an eye on your pH throughout the whole process.
If you go through with flushing your plants before harvest, you will certainly thank me; toking on your clean and wonderfully self-grown bud will be smoother than hot butter… Enjoy!