Flushing is a term we hear often in cannabis growing communities. You may have been told that flushing is essential for your plants but still don't understand how to do it properly. Flushing is easy to perform and can make your roots healthier, as well as leave you with a much tastier product after harvest. This article shows you how it's done.
The concept of flushing isn't any different to how we normally understand it. Flushing uses water to remove a build up of a material. Growing healthy cannabis normally requires us to add fertilizers, many of which contain mineral traces that build up in the grow medium and plant throughout the cycle.
The process of flushing helps to remove any excess nutrients by 'washing' the roots. Pure water is given and allowed to rush over the roots until it drains. Any mineral and salt residue is flushed out of the growing medium, meaning the plant can use up its remaining store of nutrients before harvest day.
Flushing typically takes place two weeks before the end of the flowering period, but it depends on the grow medium and how heavy the feeding schedule is. The only time we do not recommend flushing is if your are growing with organic super soils, which contain loads of beneficial microbes and organisms that can get washed away from adding too much water.
Although some people might disagree, flushing your cannabis plants is essential if you have been feeding them chemical nutrients. Cannabis that hasn't been flushed properly can taste rough and deliver a harsh smoke that does not burn nicely. It is worth putting in the extra effort so you can be sure your buds are nutrient-free.
Most cannabis nutrients that are not organic are chemically synthesised. That doesn't necessarily mean they are harmful to smoke, but your weed will have a more enjoyable flavour without them. Feeding cannabis plants right up until the day you harvest means higher quantities of those minerals are still present in the plant when you harvest. We want to help the plant remove them so we (or others) have a delicious product to smoke at the end.
Flushing can also be useful when your plants receive too many nutrients. Overloading your plants with fertilizer can cause nutrient lockout, which means the concentration of minerals around the roots is too high for them to function properly. As a result, they are unable to uptake efficiently. Heavily fed plants may also experience nutrient burn.
With commercial nutrients being so heavily concentrated, nutrient lockout can be a serious problem.
In the event of a nutrient burn or lockout, flushing your medium with pH corrected water can help to remove the build up so you can continue with the feeding schedule. This is why some growers get into the habit of flushing once or twice throughout the grow cycle, regardless of whether salt build up or nutrient lockout is an issue.
Tip: The curing process can also help to 'flush' out some out the impurities left in the bud and is a key stage in making your weed taste much nicer.
As we mentioned earlier, the flushing cycle should start around 2 weeks before you plan to harvest. It is really up to you when to begin, but if you have used a very light feeding schedule it could be a good idea to start flushing a little later.
On the other hand, if you start flushing your plants too early they might not yield as much, so make sure your plants are showing signs of ripening beforehand. Check the trichomes to see if they are changing colour or going cloudy to gauge when the right time to start flushing might be. Once around 10 - 20% of the trichomes have gone milky a cannabis plant will be getting close to harvest day, meaning you can consider starting the final flush.
Flushing cannabis plants is an easy process and can be completed in 4 simple steps. The idea is to give an initial heavy flush and then provide water for the rest of the cycle.
|
Medium |
Flush Time |
pH |
|
Potting Soil |
2 weeks |
6 - 7 |
|
Hydroponics |
3 - 7 Days |
5.5 - 6.5 |
|
Coco Coir |
1 week |
5.5 - 6.5 |
|
Compost/Super Soils |
0 Days |
6 - 7 |
Some growers skip the first step and just jump straight to feeding water. It depends on how early you start flushing in relation to the amount of nutrients they have been given. There is a risk of overwatering your plants at this stage so make sure you have a clear idea of how much they are drinking first and do not overdo it. We want to be certain that we are not inviting mold into the garden by keeping the environment too wet, especially at this stage.
Flushing in hydroponics requires you to simply add fresh water (ph 5.5-6.5) to your reservoir for the last few days of flowering. Again, it depends on how heavy your feeding schedule was. In hydroponics, there is no medium for salts to build up in so when we flush, the plants are cut off instantly from any source of nutrients other than what remains in storage. It takes time for minerals to be fully flushed out of the soil.
Growth Stage - It can be a good idea to flush whenever there is a drastic change in nutrients. For example, the switch between the vegetative stage and the flowering stage is a moment where the feeding requirements likely shift. Flushing before introducing the new routine can give plants a 'fresh' start. Plus, you'll have a clearer idea of the nutrient levels in the soil and you help to keep a stable pH.
Enzymes - The minerals and salts are compounds that can become rock solid, making them difficult to move. After heavy feeding schedules, enzyme supplements can be beneficial to help dislodge large nutrient salts from the soil by breaking them down into smaller molecules. These can be very useful at the end of the flowering period if the leaves still look overly green (normally dark green from too much feeding). They prevent the roots from absorbing more nutrients by thoroughly cleaning the soil.
Fat Banana (Royal Queen Seeds) flush by Leonweed10 from GrowDiaries.
Flushing becomes a standard practice once you have grown a few times. If you're not convinced, try growing the same plant with and without flushing. You'll likely notice the difference and be glad you decided to give it a try. And you'll save nutrients for the next grow!
How did flushing work for you? Did your weed taste better with a proper flush? Let us know your opinion on flushing down in the comments section below!
Heavy Metal Soil Contamination and Bioremediation. - Muzafar, Malik & Goyal, Pooja & Gupta, AJAI & Gupta, Suphla. (2020).
This article was updated October 2020.
