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When it comes to harvesting your marijuana plants, many people think that the timing and the actual process of harvesting are all that matters. Truth be told, however, many other aspects also come into play. One of these aspects is flushing before the harvest.
Flushing can be critical, and it isn’t too difficult to do. That being said, the timing can be tricky, and it can turn the end result into something fantastic or something terrible.
When you have already spent so much time, money, and effort on keeping your plants happy and healthy this far, it would be a mighty shame to flush incorrectly (or not at all). If you did, you’d end up with weed that is less than adequate in terms of taste and smoking quality.
In this article, we will look at the basics of flushing your marijuana plants. We will talk about what it is, how to do it properly, and the best time for flushing your plants.
Tip: make sure to download my free Grow Bible for more information about flushing
What is flushing?
Flushing is the process of removing leftover nutrients from the soil of your marijuana plants with neutral water. Water is an incredibly powerful element, and it can do wonders for your marijuana plants beyond simply your feeding regiment. It can flush away leftover nutrients and minerals, allowing the soil and plants to be fresh again.
Taking away the minerals may sound like a negative thing to do at first, but in fact, it is an incredibly helpful thing. Flushing out minerals paves the way for the roots of your plants to take in any remaining nutrients still in the soil.
Much like people or animals, it’s a way of “starving” the plants so it absorbs any fat that was left over and can be used for energy. The hard part is to time it right. You need to flush your marijuana plants at a short enough time before the harvest that the plants don’t have enough time to start becoming unhealthy.
Why should I flush?
You should flush your marijuana plants before the harvest because it will allow the buds to become smoother and higher quality. However, if you are an impatient person or aren’t good at this kind of thing, you may want to either reconsider or take extra time to plan it carefully. This is because, when timed wrong, a flush can actually have a negative effect on your marijuana plants, thus lowering the yield at the end.
The main aspect of flushing is to improve the taste of your cured marijuana. There is often a “chemical” taste with lots of marijuana, and that means there were too many nutrients at the point of harvest and the grower didn’t flush (or at least they didn’t flush properly). If you flush, however, there will only be the pure taste of the marijuana and it will even be a smoother smoke.
Some marijuana growers might argue that flushing isn’t necessary because they can just cure their weed at the very end in a way that makes up for the chemical taste and the lack of flushing. While this isn’t entirely untrue — proper curing can do wonders for fixing any flushing mistakes — it still does not replace the act of flushing altogether.
Instead, you should be both flushing out your plants before the harvest and curing them well after the harvest. This will ensure that your buds will be extremely smooth to smoke, causing no coughing or throat irritation to speak of. Maybe even the taste itself will be totally different and improved. You will just have to see for yourself!
When should I flush?
The best time to flush your marijuana plants is approximately two weeks before you plan on harvesting. However, this timing does not work perfectly for all marijuana strains and grow setups. In terms of timing the harvest itself, keep a close eye on the trichomes of your plants, because they will clearly illustrate which plants are ready to be harvested.
Plants that have mostly clear trichomes and only a few that are milky and white are too early to harvest — but are perfect for flushing. Think of it like this: two weeks after the big flush, you want most of the trichomes to have already changed color. This can be tricky, especially for new growers, but it is important to think about nonetheless. Be sure to check out my free Grow Bible for more tips on when and howto harvest.
Make sure you flush your marijuana plants when the harvest window is open. The timing also varies according to your grow medium and setup. For example, people who are growing their marijuana plants in amended soil should not flush at all, while people growing their plants in soil should flush them several weeks (1-2 or more) before the harvest. Coco growers should flush their plants about a week before harvest, while other hydroponics growers should only flush for a few days.
Other uses for flushing
Flushing is more than just a step to take just before the harvest. If during the middle of your plants’ vegetative state, they end up with nutrient burn or toxicity, flushing with water is an excellent way to get rid of those nutrients and start over with a healthier dose.
Overfeeding marijuana plants can cause a nutrient burn effect. If you start seeing the tips of your plants’ leaves changing from green to other colors, you may want to consider flushing the soil to fix the problem. But don’t flush your marijuana plants until you are certain.
Papa Green from 420magazine summarized it well:
There are three basic times/reasons to flush:
1. Pre-Harvest Flush – many folks agree that this will improve the flavor of the cured bud. If you’re using Clearex then you can flush as close as 3 days before harvest. Other methods should be done a week to 10 days before harvest and repeated three days later.
2. When you dramatically change the nutrient schedule – usually when you start Flowering, some flush entering Veg as well. This is a preventative flush. Again – not mandatory, but not a bad idea. Also, in soil, this is about the time the plants have sucked all the nutes from the soil, And before you go jacking it up with your own mix – its not a bad idea to sort of zero it out.
3. If you are experiencing Nutrient Lockout. – Usually (NOT ALWAYS!) when you have a dramatic nutrient imbalance the cure is not to try to figure out the exact one, but flush the plants, and add a fresh WELL BALANCED and MEDIUM STRENGTH dose of nutes. Now don’t go flushing at every burned leaf or tinge of yellow. Use common sense. But if you see dramatic problems, and there are no obvious signs of another problem like heat, cold, grey goop in the res, root rot, etc – then its prolly not a bad idea to flush the plants and re-fill the res.
How to flush your marijuana plants
Flushing is more than just blasting your marijuana plants with water. In fact, it should include no water blasting at all. Instead, you simply need to water your marijuana plants with pH-neutral water at the time that you normally would feed them.
It can be simply water from the tap that hasn’t been treated at all, but you should definitely check the pH level of such water to make sure that it is safe to feed to your plants. The good news is that most water from the tap in the United States qualifies, but it is always worth checking anyway because having the wrong pH and feeding it to your plants could have some major adverse effects.
When giving your plant a flush, put in as much water as possible – as much as the soil can hold. After a few minutes of waiting, pour more water into the soil so that the rest gets pushed downwards. If you are pot-growing your plants, you will be able to see the water pouring out the bottom.
Video by MedicalMarijuanaCure
You can also purchase a TDS meter to measure its total dissolved solids, especially if it looks dirty or discolored. The typical TDS (“total dissolved solids”) of normal drained water is 1300ppm. You can use this meter to keep flushing your marijuana plants until the water coming out the bottom is down to 50ppm.
‘All containers need some form of drainage. Drainage holes allow excess water and nutrient solution to flow freely out the bottom of a container.’
~ Jorge Cervantes
The water will even look cleaner as well. This is because dissolved minerals are being taken out. This little trick helps ensure the flushing method has actually worked. Remember, this can only be done in indoor grow setups with potted marijuana plants. My free Grow Bible contains more tips for growing equipment.
Be sure to acquire the correct TDS meter if you don’t have one yet.
Flushing employs several techniques that are beneficial for the removal of unwanted and excess nutrients before the harvest. One technique is stress. Flushing makes the roots of your marijuana plants stressed out to some degree, and that stress results in the faster expenditure of your plants’ energy and resources. That means that any nutrients that remained are used up, allowing for the plant to be purified of these chemicals.
Mineral salts is another technique that works well for hydroponics systems. You add large mineral particles to the solution you are flushing your marijuana plants with, and they will pull away any of the extra deposits of minerals around the roots. They are too big to be absorbed, which lets them stay outside of the plant.
The hormones technique is all about maturing your plant quickly. If your flushing solution has a natural plant hormone, your marijuana plants will naturally mature faster. It causes the minerals and nutrients in the plant to be used up while also forcing the marijuana buds to become more potent quickly by ripening faster. This makes the quality of the yield higher, assuming you harvest at the right time.
Keep an eye out for yellowing
When your flushing time begins, you should start paying closer attention to your marijuana plants. This especially means keeping an eye on their coloring. If they start going yellow a little bit, that’s completely normal for a pre-harvest marijuana plant, and you don’t have to worry. If they get to the point where all the leaves on the plant are yellow, your buds are going to start going downhill quickly (since the plant isn’t taking in sunlight energy anymore), so you need to harvest as soon as possible.
It is also important to consider the aesthetic appearance of your buds and their immediately surrounding leaves (the sugar leaves). You don’t want them to yellow before you harvest, or else the resulting weed won’t look good at all. Make sure those leaves are green when you harvest, or harvest them as soon as you see the tiniest tinge of yellow.
Sometimes, catching the yellowing of your plant in time can be difficult. This is because it can occur at an astoundingly fast rate, leaving marijuana growers dazed and confused when their plant has basically turned yellow overnight. The yellowing of the sugar leaves could even cause the buds to start turning yellow if left to their own devices.
Discoloration on your marijuana plants is not exclusive to the color yellow, either. Plants that are turning red, purple or another color should also be paid attention to. This does not apply to the buds at all (since that’s just genetics), but rather to the leaves. This discoloration indicates that the time to harvest is coming up fast. Like when the leaves turn yellow, the leaves won’t be able to absorb sunlight energy when they are purple or red (or any color besides green).
The buds themselves will have started to degrade if they are starting to turn brown and appear or feel rather crispy to the touch. This means that you must harvest them right away because they will only lose potency very rapidly at this point, and you should try and conserve as much of the remaining potency as possible.
Clearing and salt leaching solutions
It’s important to understand that certain supplements can be added to the water you are flushing your marijuana plants with. It should not be a nutrient solution, but perhaps a beneficial root bacteria (ideal for hydroponic growers), pH balancing supplements, blackstrap molasses (which can make your marijuana sweeter), and clearing or “salt leaching” solutions.
These solutions can be added to the water you flush your marijuana plants with in order to be extra effective in removing salts and minerals. If you have been feeding your plants a lot of nutrients during their regular growth, these might make for a good option to counterbalance that. Check out FloraKleen by General Hydroponics or Clearex by Botanicare for best results. If your plants obtained their nutrients from the soil itself, you wouldn’t need to use these products at all. Want to learn more about rich soil and the best nutrient solutions? Check out my free Grow Bible.
How do I flush in a hydroponics setup?
If you are growing your marijuana plants in a hydroponics setup, flushing can still play a major role for you. In fact, flushing in this type of grow medium is even easier than flushing in a soil-based (or similar) grow setup.
You will only need to make sure all of the water in the reservoir is replaced with pH-neutral water that contains zero nutrients. Plus, flushing should only be done a few days before harvest in a hydroponics system (compared to several weeks in a soil grow medium).
Thanks for reading and be sure to share your flushing experiences below!
The founder of I Love Growing Marijuana, Robert Bergman, is a marijuana growing expert that enjoys sharing his knowledge with the world. He combines years of experience, ranging from small-scale grows to massive operations, with a passion for growing. His articles include tutorials on growing... [read more]