Regardless of what plants you intend to grow, to get optimum results, raise healthy plants, and realize your maximum yield, it is critical to understand what your plants need. Cannabis is no exception. Once the basics of light, water, air, and a media are taken care of, every crop has a unique “sweet spot” where the suite of nutrient levels, electrical conductivity (EC), and potential of hydrogen (pH) converge to optimal levels. When that happens, so does the magic.
Potential of Hydrogen (pH)
Different growers may debate what is the single most important factor in getting the most out of your crops, but if the pH is not within an acceptable range, your nutrient levels and even your EC readings will be useless. Potential of hydrogen is a measure of the concentration of hydrogen (H) ions. The “p” in pH comes from the German word for power, “potenz.” A pH meter will measure the power of the hydrogen ions.
The pH scale ranges from 0.0 to 14.0 (for practical purposes this is true; there are readings outside of this range). Readings of less than 7.0 register as being acid, or “sour”; readings above 7.0 are alkaline (base), or “sweet.” A neutral pH is 7.0. There are several reasons it is important to find and maintain a proper pH for your cannabis crops (or any other crop). Not all nutrients are in an available form for your plant to use at all points on the pH scale. Some are more available in the acidic range, while some are more available in the alkaline. This means that even if your media has a proper amount or even an abundance of nutrients, they may be locked out if the pH is not correct for your crops.
Nutrient availability is not the only reason to seek ideal pH levels for your cannabis. Retention of nutrients is affected by pH. Plant nutrients may leach out more readily when pH levels are below 5.0 and above 7.5. Some elements that are required for good growth can become toxic to your plants at inappropriate pH levels. Aluminum, for instance, can become toxic in readings below 5.0. Beneficial bacteria are also affected by your media’s pH. Bacteria are most efficient at releasing nutrients like nitrogen from organic matter in your soil is between 5.5 and 7.0.
The ideal pH range for marijuana crops differs depending on the growing media, but is generally between about 5.8 and 6.5. Each strain will have its preference. If you are growing cannabis hydroponically, keep the pH between high fives and low sixes, and if you are growing in any other substrate, aim to keep the pH in the low- to mid-six range.
Electrical Conductivity (EC)
Electrical conductivity is one method of measuring the amount of fertilizer or nutrients present in your crop’s media, thus giving you an idea if your cannabis crop is undernourished or over-fed. The EC is a measure of the total dissolved solids (TDS) in your water. The readings will usually be in parts per million (ppm) or in milligrams per liter (mg/l). Either scale will give the same reading. Besides having an accurate EC meter, it is imperative to know what the EC of your water is before even starting to grow. Ideally, the EC of your irrigation water or reservoir before adding nutrients will be zero. A reverse osmosis system will give you an EC of zero if you live in an area where your water has some level of EC.
The EC value you want to see when testing your cannabis media will vary depending on the phase of growth that it is in. Like pH, the nutrient needs will also vary depending on if your crops are grown hydroponically or in any other media and can vary depending on the strain being grown.
For young seedlings, a typical EC range should be between about 0.8 and 1.3; for clones this range can dip to 0.5 to 1.3. In hydroponic grows it may be on the lower end of the range and higher in other media. During the vegetative phase, it should be higher and be somewhere around 1.3 to 1.7. This value should continue to climb leading up to and including the flowering phase, where the EC should be hovering up around two. If your EC ranges are not at or near these, it’s time to take action. If your readings are too low, slowly add more nutrients until you are at an ideal range. If your readings are too high, back off the nutrients and flush out and replace your reservoir or leach out the nutrients in your media until proper levels have been restored.
Essential Cannabis Nutrients
Entire articles, even books, could be devoted to the role of individual nutrients and their relative importance during each of the separate phases of cannabis development from seed to harvest. Cannabis is, however, not unlike any other plant in its need for primary, secondary, and micronutrients. Like other plants, it neither knows nor cares what the source of those nutrients is so long as it has them when it needs them. The choice of organic nutrients versus chemical is partially one of personal preference and, in some cases, availability. It is far easier to grow organic cannabis in soil than it is hydroponically, as there are little to no options for using organic nutrients in a hydro setup. This is because organic nutrients are not typically water soluble. They break down and are activated by the natural microbial activity in the soil. This also means they take a lot longer to work, so it is necessary to provide them to your plants earlier than with water soluble ones. Water soluble nutrients typically go to work faster and are usually cheaper than organic ones. Your plants need to have all the nutrients available.
During the vegetative growth phase of cannabis, it has a higher need for nitrogen. There are many commercially available fertilizer formulations designed specifically for this phase of growth. Keep in mind if you opt for an organic source of nitrogen, make sure that it won’t be delivering its “punch” during the bud phase; make sure that you time the fertilizer applications appropriately. A commercially available source of nitrogen fertilizer will have the first number higher than the other numbers. Typically, there are three numbers on a package of fertilizer indicating the percentage of nitrogen, phosphorous, and potassium (N-P-K). The first one should be anywhere from three to 10. Organic sources will usually be lower than water soluble ones. Some good organic sources of nitrogen include fish emulsion, feather meal, and blood meal.
During the flowering and blooming phase your cannabis plants typically need more phosphorous. As with the vegetative phase, there are products specifically designed and available to help your plants along through this important stage. This is when you want a fertilizer with a higher middle number in the range of five to 15. The same rule of thumb holds true that organic sources will have lower numbers and take more time to work than non-organic sources. Some good organic sources of phosphorous include bone meal and rock phosphate.