Experienced growers have probably heard of flushing or ‘rinsing’ their plants. This is a common practice and I will explain why.
The way plants absorb nutrients and the ratio in which they absorb them can vary based on the species, soil, ambient temperature and humidity, and the type and intensity of lighting.
Combine those variables with the fact that most people over-fertilize their plants and can’t measure which nutrients are deficient and which are too high, and you quickly come to the need to leach plants every three weeks.
Fertilizer companies vary wildly in their amount (expressed as a percentage) of each basic nutrient. While they generally all contain the 13 essential elements, the proportions of these elements can vary quite a bit from one fertilizer to another. One brand may have an NPK percentage of 10-10-10 while the other is 5-10-3. Keep in mind that labeling laws require only so much information and that nitrogen (N), phosphorus (P), and potassium (K) are only three of the 13 essential elements.
In an ideal world, the label would at least list the percentage of all macro and secondary nutrients, including calcium (Ca), sulfur (S), and magnesium (Mg). In an even more perfect world, we would have the luxury of seeing the amount of micronutrients as well, and we would be able to fine-tune them to our plants’ absorption patterns. But as fertilizer companies want to keep their ingredients and proportions their own, growers are often in the dark.
Don’t be fooled by nutritional supplements! Keep in mind that fertilizer companies are companies first and helpers second. If they think they can bottle kelp for $0.10 and sell it to you for $50, they will. They will also provide products that are popular whether they are effective or not. Phosphorus additives are a perfect example of this.
The folklore in the cannabis growing community is that flowering buds get bigger with a lot of extra phosphorus, but the science isn’t there to support this idea.
I can also tell you from hundreds of soil studies I’ve done that everyone has too much phosphorus in their soil. It is by far the most widely used nutrient in the cannabis world.
Some growers think that if your water runoff, or “drain,” is in the range of 1000-1500 parts per million (ppm) and about 6.0 pH, you should be fine. I believed this myself, but then I noticed that over time even plants with perfect drainage values could look unhealthy.
What I realized is that 1500 ppm can represent an infinite number of variations.
Of those 1500 ppm, there could be 800 ppm sulfur (a common fertilizer additive that doesn’t use nearly as quickly as it builds up), 100 ppm nitrogen (about half of what would be ideal in most varieties), and 0 ppm iron , a micronutrient that is notoriously insoluble, yet essential for healthy plants in small amounts.
So, for those of you who want a simple solution to keep your plants healthy and don’t have the time or money to analyze soil and nutrients, just rinse them every 3 weeks – or as soon as they come out less than perfect see – and then supplement them with a fertilizer mixture with an NPK value of about 3-1-2.
As for the rinsing process, the rule of thumb is to put three times the amount of clean pH-balanced water through the container as the volume of the pot itself. So for a 2-gallon pot, run six gallons of clean 6.0 pH water through it, then immediately fertilize again with a potent, pH-balanced nutrient solution.
You don’t have to spend money on fancy rinse products – tap water works just fine. Don’t let the plants sit overnight without fertilizer; they will start to die if they are drenched with no food to help them drink the water.
If a plant has already been sick and soggy before you leach it, it’s a good idea to let it mostly dry out before starting the leaching process. Otherwise, you could make it sicker by waterlogging it again, even if the nutritional balance has been restored this time. This is because the roots can be damaged from over-fertilization and associated lack of oxygen, and keeping them too wet without a break could sabotage the healing process.
Making sure you flush your plants every three weeks according to these instructions will greatly increase your overall success as a grower.
The smoke test
It would be nice to think that the appearance or smell of finished flowers could indicate whether or not the bud has been flushed properly. Unfortunately, smoking is the only way to know.
Even then, bad-tasting smoke can come from some type of spray used on the plants, or even from a substandard curing process.
The telltale sign I look for in over-fertilized buds is a hard smoke combined with a bud that turns black and stays firm no matter how long you burn it.
However, if it turns gray and disintegrates into ash, it is most likely well flushed and healthy to smoke.
Photo by Patrick Morris/Flickr