Some growers will tell you flushing your cannabis plants is pointless.
And they are right. In some situations.
Most of the time flushing is not necessary. But it can help boost bud quality when done before harvest.
And there is one situation where you need to flush your plants.
The reason many advocate against it, is that it will harm your harvest, if you do it incorrectly.
So let’s make sure you do it right.
Keep reading to learn how to flush your weed plants correctly. We’ll give you an easy step-by-step guide to follow.
We’ll also tell you the only times you should consider flushing your plants and answer the most common related questions.
- 1 How To Flush Weed Plants
- 1.1 Step-by-Step Guide To Flushing Cannabis Plants
- 1.2 Best Times To Flush Cannabis Plants
- 1.3 Flushing Marijuana In Soil Vs Hydroponic Systems
- 1.4 Pros And Cons Of Flushing Cannabis Plants
- 1.5 What If You Decide Not To Flush?
- 2 How To Flush Cannabis Plants: Related Questions
- 2.1 Can you flush cannabis plants with tap water?
- 2.2 Do cannabis buds swell during flushing? Is this a good thing?
- 2.3 What if my cannabis buds don’t swell during flushing?
- 2.4 Is flushing cannabis plants necessary?
- 2.5 How do you flush cannabis plants without overwatering?
- 2.6 Is a 1-week flush enough for cannabis plants?
- 2.7 Can you use hot or cold water for flushing cannabis plants?
- 2.8 Can you use spring or purified water for flushing cannabis plants?
- 2.9 How long do you flush auto-flower cannabis plants?
- 2.10 How much water should I flush my cannabis plants with?
- 3 How To Flush Marijuana Plants: Final Thoughts
How To Flush Weed Plants
Before you can flush your cannabis plants, you need to make sure you have the right equipment. Luckily, that is easy, since the only two items you need, apart from water, are things every marijuana grower should have anyway.
- a pH meter
- a TDS meter (total dissolved solids)
In order to properly flush your cannabis plants, you need to use a handy dandy pH meter that can measure both low and high readings to ensure that you provide the correct pH.
A TDS meter ensures there are no contaminants in the water you put in and it measures the water runoff so you can see how effective the flushing is. We have recommendations for both in this article listing the things you need to grow weed.
Ensure the pH level of water is appropriate for cannabis plants by checking that it’s between 6.0 and 6.8 if growing in soil and between 5.5 and 6.5 if growing in a soilless medium. Our article on the best water for weed plants has much more on this.
Step-by-Step Guide To Flushing Cannabis Plants
It does not matter too much what time of day you flush your plants. However, the general recommendation is to do it at either the beginning or end of a day, so you might as well go with one of those times.
Here is how you flush your plants the right way.
- Water the plants like you normally would, except do not add any nutrients or supplements to the water. You could also wait a bit longer between watering sessions to allow the plants to extract more nutrients from the soil or medium (this depends on your reason for flushing–see below).
- Repeat after 15 minutes.
- To be sure the flush went well, measure the total dissolved solids and find out how pure the water runoff is. The water draining from your pots should have a similar measurement to the water you poured in.
- Plants will always lose color after flushing. If your plants begin turning yellow quickly after flushing, get ready to harvest quickly. The buds will deteriorate once the leaves on the plant have all yellowed.
Best Times To Flush Cannabis Plants
There are three main times you might want to flush your marijuana plants. The first is shortly before harvest time.
Flushing pre-harvest removes any remaining nutrients from the soil. There are still nutrients in the plants, which the plants should then use up.
Timing is key here. You want the plants to use up all of the nutrients before harvest, so that the harvested buds are free of any minerals. This makes the buds more pure.
They burn cleaner (to a white ash) and are smoother to smoke. On the other hand, cannabis that still has nutrients in it burns to a black charcoal consistency and tastes harsher.
The problem is that if you flush too early, the plant will run out of nutrients too soon and begin to die. Obviously, this results in smaller and lower quality buds.
The best time to flush will vary, depending on what’s left of your plants, and the growing methods you used.
A good rule of thumb is to flush 2 weeks before the planned harvest. If cannabis flower is in an 8-week flowering period, flush 6 weeks after the beginning of the flowering stage.
That should more or less lead to the plants using up the last of their stored nutrients right when it is time to harvest. Some also advocate you stop watering entirely shortly before harvest.
As mentioned above, if they begin to yellow quickly, you know the nutrients are gone and it is time to harvest. You want to harvest before the buds begin to turn yellow as well.
I know this seems like a ton of extra work, but it will be worth it in the end when you get to puff, puff, pass that much cleaner and purer weed! Or sell, sell, profit!
To Recover From Nutrient Lockout
If you suspect nutrient lockout, you will want to flush your plants to basically reset the soil. Once the soil is free of nutrients, add a fresh dose, but use less nutrients than before.
It is important to be fairly certain your plants are experiencing nutrient lockout. Only flush for this reason if you notice a drastic change in your plants and you can’t find any other possible reason for this change.
When You Want To Change The Nutrient Cycle
Some growers like to flush their marijuana plants whenever they change up the nutrients they use, for example if going from veg to flower. This cleans the soil out so you can start fresh with the new nutrient mix.
Flushing Marijuana In Soil Vs Hydroponic Systems
Growing cannabis with hydroponics is probably easier than soil or coco. Soil retains nutrients, but because hydroponics uses a different growing medium, it’s easy to flush plant-related nutrients from it.
Instead of leaching or washing minerals out of the soil, for your hydroponic plants, you simply drain the system and fill it with pure water at a pH of roughly 5.8.
You can grow cannabis in coco, soil, and hydroponically. All three have their benefits and drawbacks.
Growing cannabis in soil is a great way to ensure healthy roots, but it’s difficult to control the environment of the plant.
Hydroponic cannabis plants are generally easier to maintain for beginners, because you don’t need extensive knowledge about plant care. There are fewer variables involved with growing cannabis in coco, too.
Pros And Cons Of Flushing Cannabis Plants
You may be wondering about the pros and cons of flushing. Not flushing the toilet (the pros and cons of that should be obvious), but flushing your good ol’ cannabis babies.
Flushing your cannabis plants is an important step in the cultivation process. Not only does it remove impurities, but it also helps your plant’s roots adjust to the different water pH levels.
Let’s take a quick look at the major advantages and disadvantages of flushing weed plants.
- Flushing before harvest results in higher quality buds
- Flushing can help your plants recover from nutrient lockout
- Flushing can ease the transition to a different nutrient mix
- Flushing can lead to nutrient deficiencies if you do not time it correctly before harvest
What If You Decide Not To Flush?
You do not need to flush your cannabis plants, unless they are suffering from nutrient lockout. In that case, you do need to flush so that they can recover.
Flushing when changing nutrient cycles is not necessary and I would say most growers don’t do it. But it does help make things easier on the plants and might improve the end results slightly.
Flushing before harvest is not necessary either, but when you harvest without flushing, you will probably end up with harsher buds, since they will still be full of nutrients.
It is up to you whether you consider that a problem. Many do not and many growers do not flush their plants before harvest. That said, my recommendation is to do it. I prefer the purer buds.
How To Flush Cannabis Plants: Related Questions
Next, we will answer some common questions related to flushing your marijuana plants. If you have any additional questions, please feel free to ask them in the comments below.
Can you flush cannabis plants with tap water?
Some people flush their cannabis plants with tap water, but most city water contains various minerals and other contaminants.
You are trying to remove all nutrients from the soil. Tap water will add various elements and some of those can end up in the buds.
Do cannabis buds swell during flushing? Is this a good thing?
It is important to understand that cannabis buds swell during flushing and this is typically a good thing. Your plants are no longer using any of their energy to take in new nutrients.
Instead, they use all of their energy, along with the remaining stored nutrients, to boost bud production. This results in fatter buds.
What if my cannabis buds don’t swell during flushing?
If the cannabis buds do not swell at all, then there is something wrong. It could be due to issues like overwatering, fungus, or bacteria in the plant’s environment.
Is flushing cannabis plants necessary?
We already addressed this common question above. No, you do not need to flush your plants, unless they are suffering from nutrient lockout. But we recommend flushing before harvest.
How do you flush cannabis plants without overwatering?
When trying to flush your cannabis plants, it is important not to overwater. This can lead to mold forming the soil. To prevent this, follow the advice below, in the answer to the final question.
Is a 1-week flush enough for cannabis plants?
A 1-week flush might be enough in some cases, but the standard time period is two weeks before harvest, as mentioned above. This is something you will have to experiment with, to find the ideal time to flush for your grow.
Can you use hot or cold water for flushing cannabis plants?
You can, but it is best to just use room temperature water.
Can you use spring or purified water for flushing cannabis plants?
It is best to use purified water, so that you know exactly what nutrients are in it: nothing. Spring water will contain various elements that could end up in the harvested buds.
How long do you flush auto-flower cannabis plants?
The flushing time does not change with auto-flowers. Go with the same two week recommendation.
How much water should I flush my cannabis plants with?
An easy rule of thumb to follow is to use double the amount of water as the size of the container every time you water your plants during those final two weeks.
Thus, if you have a 4-gallon pot, flush with 8 gallons of water. When the soil has dried completely, flush again with another 8 gallons of water. Keep doing this right up until harvest time.
How To Flush Marijuana Plants: Final Thoughts
Flushing your cannabis plants correctly is not hard. The key is the timing, if you do it before harvest, which is the most common situation where growers flush.
Do it too early, and your plants end up without any nutrients. Then they start dying prematurely. Do it too late, and there will still be nutrients in the buds when you harvest.
As mentioned, if it is your first time, you are best off flushing two weeks before your intended harvest time. Then adjust the timing from there for your subsequent grows.