When & How To Flush Soil Before Harvest

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So, you have successfully managed to germinate a cannabis seed, set up a good grow room or grow tent, and you’ve managed to get your weed plant to flower.

You’ve got some big, juicy, and crisp buds that smell to the high heavens and are almost ready for harvest. However, before you can harvest your crop, you need to flush the soil.

Today we are focusing on why and how to flush soil before harvesting your cannabis plants, we cover the essentials which should answer all your questions.

Just for a quick summary, flushing the soil of your weed plants before harvest involves feeding your plants nothing but clean and pH corrected water, without any kind of nutrients or chemicals.This process generally starts about two weeks before harvest.


What is Flushing Soil for Harvest

Flushing the soil of your weed plant before harvest involves supplying your plants with large amounts of fresh water.

The aim here is to flush out any remaining nutrients, fertilizers, chemicals, and any other such substances.

When you flush your weed plant before harvest, you are removing nutrients and chemicals from the equation.

Any nutrients, fertilizers, and other growing agents used during the growth process will be used up by the plant, thus leaving you with chemical and nutrient free buds.

Why Flush Weed Plant Soil Before Harvest

Related to what we talked about above, the reason why you want to flush the soil of your weed plant is to get rid of any remaining nutrients, chemicals, and fertilizers used during the multi-month cannabis growing process.

The reason why you always want to flush the soil before harvest is exactly because of this, because you don’t want any nutrients or chemicals left in the marijuana when it comes time for harvest.

For one, various nutrients and growth assisting chemicals simply are not healthy to smoke, vape, or ingest.

You don’t want to be smoking nutrients or fertilizers, as that is super unhealthy, and can make you feel very ill.

If you smoke weed which has not been properly flushed for a prolonged period of time, it may lead to some more severe and long lasting health consequences.

There is also the fact that weed which has not been flushed properly can also taste very bad, especially when smoked or vaped.

How To Flush Soil – Quick Summary

Flushing the soil before you harvest is actually extremely simple at takes far less work or effort than supplying your plants with nutrients and fertilizers.

The whole point of this exercise is to give your weed plants water, clean water without any additives whatsoever.

The only thing you need to make sure of is that the water is pH neutral, or close to it anyway. Simply supply your weed plants with water as you normally would, but without any kind of additives.

This will cause the weed plant to use up any remaining nutrients in the soil and in the plant itself, so by the time you have to harvest your marijuana, there should be absolutely no residual nutrients or chemicals left, thus leaving you with clean weed that is ready to be dried, cured, and consumed.

When To Flush Soil Before Harvest

The other important thing for you to know here is when flushing needs to be done. To know when to start flushing your soil, you also need to know when your marijuana is ready to harvest.

For instance, if your weed plant, the specific strain in question, has a 10 week flowering period, you will need to start flushing the plant when it starts the 9th week of the flowering period.

In other words, a weed plant needs to be flushed for a total of 2 weeks prior to harvest, with some people even going as far as 3 weeks.

Now, this is going to depend on how long the flowering period of your plant is, and no, not all flowering periods are the same.

Therefore it also helps if you know how to tell when your weed plant is almost ready for harvest, which is usually done by taking a close look at the shape and color of the trichomes, the hairy crystals on the outside of the buds.

Other Reasons To Flush Cannabis Soil

There are a couple of other reasons to consider flushing the soil besides harvest.

Reason 1;

If your weed plant is transition from the vegetative growth stage to the flowering growth stage, it maybe beneficial to reset the soil as the transition occurs.

The reason for this is because weed plants need different nutrients, or at least different levels of nutrients in the flowering stage when compared to the vegetative stage.

Flushing is a good way to reset the soil for this transition, but this should really only be done for 2 to 4 days at most.

Reason 2;

Another reason why you might consider flushing the soil is in order to combat nutrient burn.

If the tips of the plant’s leaves are turning brown or yellow, and they look as though they have been burnt, chances are that you have been giving your plants way too many nutrients.

Over time, overfeeding your weed plant with copious amounts of nutrients and fertilizers can kill them.

Therefore, if you notice nutrient burn occurring, flushing your plant for a few days to help remove excess nutrients might just save the crop from certain doom.


The bottom line is that flushing soil before harvest, at least 2 weeks before harvest is absolutely mandatory.

You don’t want to be ingesting, smoking, or vaping all of those nutrients and chemicals. It’s not healthy and it doesn’t taste great, so take the time to always flush the soil before harvest.

It’s very easy and takes less effort than providing your plants with nutrients, and yet, if you don’t flush the soil, you will end up with weed that tastes horrible, is unhealthy, and probably shouldn’t be consumed.

Photo credit: DanGoofy @ Flickr CC


My passion for the sticky icky started nearly a decade ago, and it all began when I first laid my eyes on the beauty that is the marijuana plant.

I cover all aspects of growing from equipment recommendations to plant health/care tips to help both new and experienced growers.