Flushing the marijuana plants before harvest can make all the difference in the best bud, or horrible hash. This small task is simple and super easy to do. Just add water! Flushing your marijuana plant is kind of like a giving it a detox from all the nutrient salts and nourishing chemicals that may have stored in your cannabis plants’ tissues. Your plant stores these nutrients in their leaves in case they don’t get fed again for a while.
Be very careful, as the timing of the flush can play a critical role in this process. 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.
WHAT IS FLUSHING?
The act of flushing a plant is using plain water to actively remove any nutrients in the soil. A large amount of water is passed through the soil and drained away on a regular basis. Any minerals and nutrients present in the soil are washed away over time by the water, leaving the soil clean.
Why would you want to strip away all the minerals from the soil? Isn’t this hurting your harvest? It actually helps your harvest a significant way. When the nutrients are removed from the soil, it forces your cannabis plant to use up any remaining nutrients still present in the plant. It is a lot like the human body. We take in a lot of food and, what we do not use is turned into fat. In extreme situations where food is scarce, the body relies on this stored fat for energy.
As flushing forces cannabis to use up any remaining nutrients left in the plant, none should remain to taint the use of the harvest bud. However, if done to early, it can leave your plant unhealthy, so timing is key.
THE BEST TIME TO FLUSH YOUR CANNABIS
Flushing is usually commenced two weeks before harvest. If the plant has an eight-week flowering period, the flushing will need to take place six weeks after the start of the flowering stage. It is best to take a close look at the trichomes on your plant to assess when your cannabis is likely to be ready for harvest. If the tiny trichomes are just beginning to turn from clear, to a cloudy and milky colour, this could be a good indication that the plant can begin flushing. It should be timed so that the majority of trichomes will have fully changed to the desired colour for harvest after two weeks – this gets easier with experience, so stick with it!
Flushing can also be a good way to reset the soil while a plant is in the vegetative state. Sometime, growers will accidently overfeed their cannabis, causing the tips of the leaves to begin changing colour and shriveling. This is called “nutrient burn”. Flushing the soil can remove the excess nutrients, helping avert the problem. However, it is a drastic measure at this phase of growth, so be sure that the problem is nutrient burn, and not something else first.
HOW TO FLUSH CANNABIS
Flushing your cannabis plants is a straight forward process. Untreated tap water is all you need to use for flushing, just be sure to make sure the pH is at a safe level for cannabis. pH test the water to make sure it is in the optimal range for cannabis plants, which is between 6.0 and 6.8 for soil. The pH can be as low as 5.8 in hydroponic systems. It is important to pH the flushing water to make sure that some metals and salts will be properly removed during the process. Most well water contains a healthy pH level and will not need treatment, but if it is necessary for you to add treatment to adjust the pH of your flushing water, feel free to do so.
Flood the soil with as much fresh water as it can hold. Leave this for a few minutes to allow all of the nutrients to be picked up, the flood the soil again to flush it all away from the plant. If you are indoors using pots, notice the colour of the water that is draining from the bottom of the pot. It will be stained and look dirty. Water the plants until the drainage runs as clean as possible. When properly flushed, drainage water should run clean. It may be necessary to saturate the growing medium/container completely, then add more fresh water after it begins to drain. Some growers go as far as to measure the total dissolved solids (TDS) in the drain off with a TDS meter. Though, this is not an essential tool for most home growers.
Flushing Too Early
When you flush a cannabis plant too early, you’re stunting its growth because buds aren’t getting enough nutrients to develop properly. Without being given the right amount of nutrients during the most crucial parts of the flowering stage, the potency, quality and weight of your buds can also be lower. Growth is stunted during the most important parts of the flowering stage, and yields are reduced. Potency may be lower because buds didn’t have the nutrients needed to develop THC properly, and if buds are also harvested early it reduces the potency even further! The appearance of buds can be affected, as a plant left too long without nutrients starts developing nutrient deficiencies that can spread to the sugar leaves on your buds, causing unsightly yellow leaves. Although this doesn’t negatively affect how the bud smokes, taking care of your sugar leaves until harvest is very important to get the best-looking buds (this is also another reason why it’s important to avoid too much nutrient burn).
Not pH’ing Your Water During Flush
Another common problem growers have is they stop maintaining pH when they start the flush. Even during the flush it’s important to maintain pH at the roots to make sure your plant can properly use the nutrients available. It can help prevent yellowing and spots on the leaves during the flush; when the pH is too high or too low at the plant roots, it makes certain nutrients unavailable to the plant and increases the chance of seeing nutrient deficiencies. The plant also tends to absorb more aluminum and salts out of the water when the pH isn’t in the correct range. Maintaining pH throughout the flush will help prevent deficiencies and unwanted salt absorption, while still allowing your plant to use up its extra reserves of nutrients in the buds!
How Long To Flush?
It’s generally recommended to flush plants for a few days to 2 weeks. I think this is a pretty good standard to go by. Unless you’re growing in amended super soil, flushing for longer than 2 weeks without nutrients is likely to stunt growth of the buds, which we don’t want in the flowering stage! Many growers agree that a few days to 2 weeks is a good amount of time to flush
- Soil growers should flush the longest, from 1-2 weeks. This is because there is still some amount of nutrients left in the soil.
- 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.
- 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.