If you're looking for a more relaxed effect, I recommend starting the flush when just about all the trichomes have already turned cloudy. Harvesting on time gives more potent results and bigger yields than harvesting early, so it's imperative to avoid flushing too early! The harvest window lasts for a few weeks and with this method your buds will still be ready to harvest at the end of the flush, without the chance of having started too early. 2.) Provide only plain pH’ed water to plant until harvest (from a few days to 2+ weeks) You're going to do everything you normally do when it comes to watering, except without any additional nutrients or supplements. Don't give more water at a time than normal, because this increases the chances of your plants getting overwatered and showing deficiencies/symptoms caused by that problem.
Soil Growers Flush 1-2+ Weeks – Soil growers should flush the longest, from 1-2 weeks. This is because there is still some amount of nutrients left in the soil. For super soil growers who haven't used any nutrients from seed to harvest, you don't have to worry about flushing because you've been giving plain water from the beginning. Your microorganisms in the soil have fed nutrients directly to your plants as needed, and it's very unlikely you have any type of nutrient build-up. 1 Week – Coco coir does not hold onto a lot of extra nutrients and just a watering or two with plain water will wash most nutrients away. Therefore growers utilizing coco coir should only flush their plants from a few days to about a week, depending on how fast the plant is turning yellow. DWC/Hydro Growers Flush for a Few Days – When a hydro/DWC grower changes their reservoir to plain water, their plants literally have access to almost zero nutrients immediately. Because of that, a hydro grower should usually only flush their plant for a few days before harvest to prevent early yellowing.
Exceptions to the "No Supplements" rule: Beneficial root bacteria – Hydroponic growers should continue using products with beneficial root bacteria like Hydroguard right up until harvest. These products do not contain any nutrients but will protect your plants from root rot. Continue to manage the pH of your water as normal – PH Up and Down products don't contain added nutrients. If the pH is too high or too low, it makes certain types of salts and aluminum more available to your plant roots. You don't want your plant absorbing that stuff up right when you're trying to flush the buds! Blackstrap molasses – This all-natural bud sweetener is safe to use up until harvest in coco or soil grows (1/2 tsp per gallon of water), but not in hydro. "Clearing" or "Salt Leaching" Solutions (below) – These supplements have been specifically designed to help remove extra nutrients during the flush. Even during the flush, it's still important to manage your pH. Many growers agree that a few days to 2 weeks is a good amount of time to flush. Plants in soilless mediums like coco or hydro can't be flushed as long as plants in soil because they will run out of nutrients too quickly. For hydro you may only be able to flush for a few days. Flushing too long or starting too early increases the chances of reducing yields and running into unpleasant looking nutrient deficiencies. These products are formulated to help remove extra minerals or salts when flushing the plant, which may reduce the chance that these leftover minerals or salts end up altering the smell or flavor of your buds. They're meant to be used if you've been giving your plants extra nutrients in their water. They aren't necessary when the plant has been getting all its nutrients from the soil. FloraKleen (by General Hydroponics) 3.) Watch out for early yellowing. During the flush before harvest, it's important to keep a close eye on your plants. Your plant can turn yellow almost over night in certain situations. Although it's normal to see some amount of yellowing before harvest, it's important to harvest before the sugar leaves on the buds have turned yellow. Try to harvest before the green sugar leaves (small single-finger leaves directly attached to buds) start turning yellow. In the following cases, many of the fan leaves have turned yellow during the flush, but the small leaves on the buds themselves still appear green. You can see the sugar leaves are mostly still green, but many of the fan leaves are pale and turning yellow. This auto-flowering plant is ready to harvest, too!
If you wait any longer the yellowing may spread to the buds. If the leaves of your plant have turned completely another color like red or purple, that is also a sign the end is near (not talking about when the buds themselves turn pink or purple, as that's caused by a different genetic trait and doesn't have anything to do with the leaves). Even for plants where leaves changing colors is normal, it usually only happens when harvest time is coming soon. Your plant can't really make energy from light after the leaves stop being green. That means you should plan on harvesting within a week of leaves going completely purple, and possibly even sooner if the buds themselves start looking discolored. In the following picture the buds continue to look pristine so far, but the purple leaves are a sign that the grower should plan to harvest soon to avoid letting the buds themselves get discolored or crispy. Try to harvest your buds before the sugar leaves and/or the buds themselves actually start turning yellow, or buds appear burnt.
Although discolored sugar leaves doesn't affect the quality/potency of the buds, it does affect the appearance (your buds won't be as pretty). Additionally, once all the leaves are yellow your buds won't really mature a whole lot more, and buds can quickly further deteriorate in health and lose potency.