Cannabis is a living plant that requires nutrients – just like you do. Of course, the way a cannabis plant eats is much different than the way we eat. The roots of the plant absorb nutrients which are available within the soil and water. Making sure that your cannabis plant has all of the essential things that are necessary for nutrition is paramount to preventing slow growth, damaged foliage, or diminished yields.
Cannabis nutrient deficiencies can be hard to identify, and sometimes overwhelming to learn how to treat. In this guide we’ll discuss a few of the most common cannabis nutrient deficiencies as well as discuss prevention and a few simple tricks that might easily correct problems.
Let’s start, by discussing some of the essential nutritional needs of the cannabis plant through its life.
The three most macro-nutrients for healthy cannabis growth are Nitrogen (N), Phosphorus (P), and Potassium (K), and the value of these elements in any nutrient product, is expressed on the label of fertilizer products as N-P-K.
During the vegetative development of the cannabis plant’s life, nitrogen is the element we often find most abundant in the nutrient products designed for this phase. 6-3-7 might be the N-P-K value that you find on the label of one of these products.
4-10-12, for example, might be the N-P-K value of a nutrient product designed for the flowering phase of the plants life. In this example we see that there is much less nitrogen in proportion to the phosphorus and potassium values. This is because, during the plant’s flower development, it will benefit from copious amounts of both of these elements, P and K, while nitrogen plays a lesser role. Phosphorus is important to building heavy flower sets, while potassium is necessary for the plant to make use of this phosphorus.
There are 3 other macro-nutrients that are also needed in great supply. Calcium (Ca), magnesium (Mg), and Sulfur (S) are incredibly important to the biological processes going on in the plant throughout its lifetime. While many potting soils have plenty of these elements for the onset of vegetative growth, the supply is often depleted quickly by the time flowering occurs, or in the case of extended vegetation times. Most vegetative and flowering base nutrients contain enough of these three compounds in order to prevent depletion, however there are methods for prevention and treatment of these deficiencies.
The micro-nutrients are; boron (B), zinc (Zn), manganese (Mn), iron (Fe), copper (Cu), molybdenum (Mo), chlorine (Cl), and constitute in total less than 1% of the dry weight of most plants.
A micro-nutrient is an element of plant nutrition which is needed in much smaller quantities than the three macro-nutrients are needed. This doesn’t mean that they aren’t equally as vital to producing heavy harvests of the best buds – but simply that very little goes a long way with these elements. In fact, most quality potting soils will have most if not all of the micro-nutrients that will be needed for the life of your plant already contained within them! It is rare that you might find yourself deficient in these micro-nutrients when growing in soil– however if you do, it is probably a good idea to take a look at the quality of the soil that you have chosen to use.
Most of the formulations of nutrient products on the market are well engineered in a way that the elements needed for vigorous plant growth are well divide into the ratios and quantities that the plant will need in each stage of its life. This means that a nutrient product meant for complete nutrition of the vegetative phase of growth should have all or most of the macro-nutrients and micro-nutrients necessary for success.
Because nitrogen is the most consumed element during the vegetative phase, the first sign that your plant is lacking nutrients is usually a nitrogen deficiency. Deficiencies in nitrogen are expressed as a yellowing and dying off of the older foliage, at the bottom of the plant and works its way up to the top of the plant if given time to progress. The plant is consuming itself and its supply of nutrition. The easiest way to fix this problem is to simply increase the concentration of the nutrient solution you give to the plants during watering. If you have been only using water, and this is the first time that you seeing yellowing at the bottom of the plant – this is an indication that your plant has consumed the nutrient reserves which were provided by your soil, and that its time to start using nutrient products!
Keep in mind that too much nutrient is often seen at the newest growth, as burnt tips – the opposite of where you might be looking on the plant for a deficiency in nitrogen.
During the first few weeks of flowering might be when you first discover signs of a phosphorus deficiency. This could be an indication that its time to switch over to a flowering nutrient product, which has higher amounts of phosphorus compared to nitrogen, or to increase the concentration of the nutrient solution which you are using to water the cannabis plants. Deficiencies start in the lower and older leaves, and necrotic spots often form. There is yellowing of the leaves as well.
Like phosphorus, you are likely to notice deficiencies in potassium towards the onset and start of flowering, as the plant changes its needs to consume more of these two elements compared to nitrogen. Potassium deficiencies are often expressed as bleached or chemically burned foliage. In fact, sometimes potassium deficiencies can be mistaken as light burn and vice versa.
Calcium and magnesium deficiencies often show up alongside each other, and can also be prevented and treated alongside each other.
Magnesium deficiencies tend to appear on older leaves first and can be difficult to diagnose, often as is the case for calcium deficiencies. Necrotic spots and quickly losing leaves can be an indication of deficiency. Because they are often paired with other deficiencies. This can be an indication of pH issues.
Many times, suspected nutrient deficiencies are simply the result of improper pH values. Also, these are the two most common deficiencies that might occur which aren’t fixed by simply raising the concentration of your nutrient solution by adding more of the base nutrient product. Many base nutrient products lack the amount of magnesium and calcium necessary for a cannabis plant to thrive. Soils also tend to lack the stock of these elements needed throughout the plants life.
According to Emilio at BioTabs in Barcelona, the easiest way to treat a cal/mag deficiency is also the best method for preventing it.
Dolomite Lime Powder. This is a type of limestone which will provide lots of calcium and magnesium to your plants. He suggests 2g of powdered dolomite lime per 1 liter of soil when preparing your soil before potting your plant to prevent deficiency and supply all of the calcium and magnesium that might be needed. On the other hand, you can also add the powder to your solution when watering if you discover that there is a deficiency during the course of the plants life!
Franco Casalone, famed Italian Guru of cannabis (in Italian), has had experience in his garden recently demonstrating that high levels of red light compared to blue light during flowering ultimately increases the rate of maturation in his cannabis plants but also resulted in magnesium deficiencies that the same varieties under blue lighting did not exhibit. This is an excellent example of how the lighting systems you use can change the nutrient demands of your plants. Some growers report unique nutrition demands and deficiencies when growing under LED lighting, as well.
Before deciding that you have a lack of any specific element in your soil, first its important to make sure that whatever is already in your soil is available to your plant. Metaphorically speaking, pH is the controller who decides which elements in the soil are available for absorption by the cannabis plant roots, and at what ratios. Different swings and changes in the pH values can result in certain elements being unavailable for your plant to absorb despite being present. Keep in mind that in soil, pH values between 6-6,5 are considered the sweet spot for nutrient absorption. Check the pH values of your water and nutrients at every watering.
Living soils are incredibly interesting ways to produce some of the most incredible cannabis. BioTabs offers a line of products which take away the complication of living soils and make it easy to do at home with only a few simple products. The benefit to living soil cultivation is that the pH and quantity and ratio of nutrition is maintained by a living ecosystem within the soil. Rather than filling the soil of your plant with nutrient solutions – you practically only have to add very pure water, and from time to time feed the biological activity within the earth. This is a fantastic method for letting the plant do more of the work for you!