Nutrient Ratio Chart
This mission critical chart shows the average PPM of each element needed for growing Cannabis indoors as well as the typical ranges. Notice how Potassium K and Sulfur S have the highest average number that you will need in your nutrient solution. This is really important info, Sulfur is typically found in fertilizers as some other elements Sulfate like Ammonium Sulfate, Copper Sulfate or Zinc Sulfate and as a result is seldom listed in a fertilizers nutrient breakdown like the other elements. Potassium is one of the Big 3 macronutrients and cannabis wants more of it than any of the others. During the Vegetative stage Cannabis wants a ratio of 1.5 to 1 of Potassium to Nitrogen. In the Flowering stage it wants even more at a 2 to 1 ratio. Paying close attention to Potassium will set you in the right direction for success. Supplementing your regular fertilizer with something like Langbeinite will give the extra Potassium as well as Magnesium and Sulfur. Both Potassium and Sulfur contribute highly to the fragrance and flavor of Cannabis’ medicinal compounds.
Chemical and Organic Nutrients
If you are growing hydroponically you will probably be using chemical fertilizers. The number of companies manufacturing chemical nutrients can be blinding. Many companies make nutrients that are intended specifically for cannabis cultivation but if you know what you are doing you can surely use just about any manufacturer provided you give the plant all the elements it needs and in the right amounts. Specialized chemical and organic fertilizers separate their nutrients based on the growth stage of the plant. In addition to this, there are many additives one should consider that can help you fine tune your feeding by adding in supplemental ingredients like amino acids, beneficial bacteria and mycorrhizae.
Both liquid chemical and organic nutrients have a shelf life and can go bad. When liquid chemical nutrients go bad elements fall out of the solution and form crystals that accumulate and sink to the bottom. If you have ever used Fox Farm Grow Big you know what I’m talking about. Organic nutrients can also turn nasty as the microbes within continually churn the solution and over time become anaerobic until it is more like a septic pipe than anything your plants will want. So be mindful of this and only buy what you need for the season or you are throwing your money away. Also be careful about buying online as you don’t really know how long something has been sitting around before you get it.
For a breakdown on the specific nutrients used for growing Cannabis check out the Cannabis Nutrients & Deficiencies page.
Different Plants have Different Nutrient Needs
The most important thing about nutrients, whether you decide to use chemical or organic based fertilizers, is how much to use. Most fertilizers purchased in specialty gardening shops will have recommended dosage instructions which may or may not be right for you. Different varieties of cannabis for instance will have different nutritional requirements with some being able to take significantly higher quantities than others. Using the instructions on the bottle may be toxic for your variety. So the best practice if you are unsure is to start light and then if needed increase the frequency if deficiencies start to appear. Check out the Nutrient Runoff Testing page for more information about different feeding routines to maximize your plants nutrient uptake. Also, be aware that different sized plants will also have different needs, a large plant can utilize a higher PPM TDS than a small plant.
Don’t try to wing it by scheduling feeding by memory, you will fail. Print out a 3-4 month calendar and hang it in the garden. Keep an exact accounting of what was done on each day. Keep track of things like if you used nutrient or plain water, if you applied a mycorrhizae solution, when you transplanted to larger containers, when you adjusted light schedules, and when you notice deficiencies or signs of over fertilization. Keeping a specific accounting day by day will make you more successful in future sessions.