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When, how and why to wash roots

By: Daniel C. Grow

In the world of self-cultivation, there seems to be a debate on cannabis root washing. Opponents believe that doing so before harvest will deprive roots of vital nutrients. On the other side of the divide, proponents claim that it releases plants from excess of contaminants, producing higher quality marijuana. In this article, we will explore the truth: what is it exactly, why it is so important and how best to do it for maximum benefit.

Before we get into the reasons why it is important to wash the roots of marijuana plants, we must understand exactly what it is. This consists of watering the plants with water without any added nutrient for a period of time before harvest, from one or two days to a week or more, depending on the growing medium and the purpose we seek.

During the growth and flowering cycle, plants store excessive amounts of nutrients, salts and other compounds, both in the roots and in the plant environment. If you don’t allow plants to get rid of these excess compounds by washing their roots, the end product will be much harder and more bitter in taste. It can also cause the resulting cannabis to suffer other negative side effects, such as black ash and an unpleasant chemical odour. And the truth is that not unloading nutrients to the plant before harvest can greatly lower its quality.

What is “root washing”?

Basically, this term refers to watering only with water and not using more nutrients after a certain point of the flowering cycle, usually during the last two weeks of life. The best way to understand how it works is to look at it from two different points of view:

  • Using tap water or an enzyme solution to rinse the roots will allow the undissolved salts that have accumulated in the culture surroundings to be removed. If you are using mineral or hydroponic nutrients, during the vegetative and flowering stage they will have accumulated, so using pure water gives undissolved salts the opportunity to dissolve.
  • Cannabis plants are left to exhaust all their internal reserves and, in return, they will make a final effort to increase size, weight, resin, terpenes and flavonoids. A good analogy would be when a person is fasting, so all his or her internal reserves will be depleted accordingly. Many growers believe that a final wash ensures that the plant uses all the stored sugars and absorbs all that is left in the middle, resulting in fatter and tasty buds.

When to do a cannabis root washing

Finding the best time will vary depending on how close the harvest time is, the methods used and the grower knowledge. In general, washing is usually done when the trichomes begin to acquire a cloudy white colour that determines the ideal ripening window. Time is key because if you wash too soon, you will have cleaned an immature plant and if you wash too late, with too little or sporadic water the accumulated salts will not be eliminated.

Growers usually use tap water to wash the roots for different reasons, but the time for each purpose is different. Here are the three main reasons to do so:

  • To solve the problems related to nutrients: the cultivator does a root washing if the plant doesn’t look healthy or shows signs of nutrient lockout, which is a salt build-up that hinders the nutrients in the growing medium. You may see yellowish, burned, claw-shaped or abnormally dark green leaves that show signs of this lockout.
  • To get a better product: washing the roots before harvest reduces certain fertilizer flavours in the buds, which makes the smoke softer and the grass tastier. During the final wash, you should start to see the yellowish colour in the fan leaves and the vegetable canopy discoloration, a good sign that the nutrients are being properly depleted.
  • To vary feeding in order to switch to flowering: some growers like to wash the roots when they go from the vegetative phase to the flowering phase because the nutritional needs of the plant change. Washing the roots in that cycle change is not harmful when you want to avoid the accumulation of nutrients from the previous stage.

How to root wash marijuana

To perform a deep root cleaning it is advisable to apply two complementary techniques: substrate washing and irrigation washing.

Substrate washing

It is the most common method to solve an excess of nutrients. To perform it optimally it is necessary to place the plants in a shower or bath and apply water directly on the substrate for about 25-30 minutes. Just keep the shower head on top of the pot, interrupting the passage of water, briefly and successively, so that the water drains gradually and the substrate is cleaned effectively and progressively.

At first the water will come out quite dark, but it will be clarified as the substrate is cleaned. In the end, the water would have to come out practically clean. To make sure that we are doing the right thing it is convenient to make measurements of the water EC (electroconductivity) that drains the pot, at the beginning and at the end of the process. It is ideal that the water coming out is as close as possible to the reading of the neutral water coming in. Also do not forget that the temperature should not be too hot or too cold: the ideal is 20º-22ºC.

Irrigation washing

This is the most commonly used method for obtaining a quality product at the end of the harvest. To do this, you have to water the plants as you normally feed them, but without giving them any nutrient or supplement, during the last 2 or 3 weeks, with clean water containing a pH of 5.8 to 6.2. Enzymes can also be added to the water once or twice a week so that mineral salts in plant tissues and roots dissolve faster. Two weeks of washing are sufficient for the final product to be completely free-impurities.

Once the roots are washed, we must stop using fertilizers and nutrients and only water it if we see that the substrate dries. This will force the plant to use its food reserve, change its appearance and turn yellow. That’ll tell us that root washing worked. But it is essential to harvest before the leaves have completely yellowed, as the buds will begin to deteriorate.

It is recommended to water at the beginning or the end of the day when the plants are fresher, as this reduces perspiration so that they do not hydrate too much. And make sure you don’t harvest dried or withered marijuana plants; they should be nice and healthy when you cut them, to preserve the most terpenes that will give your cannabis the flavour it deserves after so many months of work.

Kannabia Seeds Company sells to its customers a product collection, a souvenir. We cannot and we shall not give growing advice since our product is not intended for this purpose.

Kannabia accept no responsibility for any illegal use made by third parties of information published. The cultivation of cannabis for personal consumption is an activity subject to legal restrictions that vary from state to state. We recommend consultation of the legislation in force in your country of residence to avoid participation in any illegal activity.

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