Just like any other cultivated crop, in order to live and thrive cannabis plants require what are referred to as essential elements. These essential elements each play key roles in plant development and are deemed essential because, without them, the plants would not be able to develop properly. People who grow cannabis will, at some point, experience a nutrition deficiency. In other words, most growers will experience a situation where less than optimal growth occurs due to the plant’s inability to absorb one of the essential elements. In most cases, a nutrition deficiency is treatable and correctable fairly easily. However, finding the source of the problem is extremely important, especially if it becomes a reoccurring issue. Treating the symptoms of a deficiency will help, but if the source of the problem is not rectified, chances are good that the plants will continue to suffer in subsequent grow cycles.
Most of the plant nutrients made for growing cannabis are balanced and contain all of the essential elements needed for accelerated growth. However, it is not enough to provide just the plants with the essential nutrients; it is important to provide the root system (and the microorganisms in and around the roots) with the proper conditions also. The potential hydrogen, or pH, of a soil, medium, or hydroponic solution represents how acidic or alkaline that soil, medium, or hydroponic solution is. It is actually the pH level of the area around the plant’s roots that mainly influences the availability of nutrients for plant absorption.
For soil gardening, the ideal pH range falls just below neutral, in the 6-7 pH range; with maximum absorption around 6.3-6.8. A slightly acidic pH is ideal for the reproduction and functioning of the beneficial microorganisms that help break down organic matter into soluble nutrients. When pH values drop below 6, there is a significant decrease in the availability of nitrogen, potassium, sulfur, calcium and magnesium, but the largest decrease is in the availability of phosphorus. Many times horticulturists experience phosphorus deficiencies, not because there is an inadequate amount of phosphorus in the soil, but instead because the pH of the soil has become too acidic.
Hydroponic gardeners will find the ideal pH for nutrient absorption is slightly more acidic than for soil gardening. A hydroponic system is less dependent on the microbial life that is normally harbored in the soil. Hydroponic nutrients are already broken down into a soluble form. This bypasses many of the functions performed by the beneficial microbes, thus changing the optimal pH range for nutrient absorption. The ideal pH range for hydroponic gardening falls in the 5-6 range; with maximum absorption around 5.5-5.8. Unlike soil, the pH value of a hydroponic solution can fluctuate rapidly. This is why it is so important to monitor the pH of the solution daily, if not more often.
The pH of the soil has a large impact on the availability of nutrients so it is of the utmost importance that a grower understands the factors that most commonly affect the pH. The pH of a nutrition solution is most influenced by the water source, the nutrients used, and the growing medium.
If a gardener is experiencing the signs of a nutrient deficiency, even after he or she has addressed the pH of the growing system, he or she should attempt to treat the specific deficiency being experienced. Many times nutrient deficiencies mimic each other, which makes positive identification even more crucial to correcting the issue. Here are some of the most common deficiencies experienced by cannabis cultivators and ways to quickly correct those deficiencies.
Nitrogen is the most common deficiency experienced by cannabis plants. A plant deficient in nitrogen will have pale or yellowing leaves that start at the bottom of the plant and work their way up to the top of the plant. Plants can be treated with a fertilizer with a high available nitrogen content. Foliar treatments of soluble, high nitrogen fertilizers can help correct this deficiency fastest.
As previously mentioned, a phosphorus deficiency is most often due to a pH level that has become too acidic. Plants with phosphorus deficiencies exhibit slow or stunted growth, regardless of how optimal the environmental conditions may be. Red stems and smaller than normal dark green leaves are also signs of a lack of phosphorus. Plants can be treated by feeding them a blooming fertilizer (even in the vegetative stage) which contains a higher ratio of phosphorus in relation to the other macro-nutrients.
The most identifiable symptoms of a potassium deficiency in cannabis plants are dead, brown spots forming on the lower leaves. Leaves may also suddenly turn yellow and die. Treat plants by supplementing a soluble fertilizer with sufficient potassium or make a tea out of K-mag for a foliar or drench application.
A lack of calcium will generally cause the medium to become acidic and this can cause a series of other problems (such as magnesium, phosphorus, or iron becoming unavailable for absorption). Hollow stems found on harvested plants are telltale signs of inadequate calcium. It is a good idea for growers to supplement a calcium additive during all vegetative and early flowering growth. To correct a calcium deficiency, start by making sure a calcium supplement is part of the fertilizer regiment and then foliar feed 1-2 tsp of dolomite lime per quart of water.
Magnesium is another very common deficiency for cannabis plants. Plants without sufficient magnesium will usually exhibit yellowing leaves on the lower portion of the plant and, in some cases, will turn white. The veins of the leaves will remain green. Leaf blades can crisp and curl upward. A good treatment for a magnesium deficiency is to use 2-3 tsp of Epson salts per gallon of water as a foliar or soil drench.
With a boron deficiency, the new, emerging growing shoots will appear burnt, brown, or gray. This deficiency can be treated with 1-2 tsp of boric acid per gallon of water as a foliar or soil drench.
Usually caused by pH imbalances, iron deficiencies in cannabis plants turn leaves on new shoots bright yellow, while the veins remain green. The best treatment is to supplement a fertilizer with a higher percentage of iron.
Cannabis plants that have white areas on the tips of the leaves or intermittently between leaf veins are displaying a zinc deficiency. This is a common problem in soils that are or have become alkaline. If experiencing a zinc deficiency, a gardener should retest the pH of the solution and medium. In most cases, a zinc deficiency is related to a fluctuating pH. If the pH is in check, the gardener should treat the plants with a foliar application of a fully soluble fertilizer that contains zinc.
When growing cannabis, many horticulturists attempt to push their plants to the maximum. Put another way, the majority of cannabis growers try to provide the ideal atmospheric conditions so their plants will uptake the largest amount of nutrients and grow at the fastest rate possible. In some cases, a horticulturist may make the mistake of believing that more fertilizer will equate to faster growth. Unfortunately, instead of increased growth rates, this usually causes a nutrient lock-out, also known as over-fertilization or toxic salt accumulation.
Over-fertilization in cannabis plants is often misdiagnosed as a nutrient deficiency. If there is leaf burn starting at the tips of the leaves and working its way up the “saw blade” of the leaf, the problem is most likely caused by over-fertilization, not a nutrient deficiency. When a grower experiences over-fertilization, he or she must remove some of the built up salts from the medium. A good place to start is to leach the soil with a diluted fertilizer (1/4 strength) and wait until the plants exhibit signs of recovery before increasing the fertilizer strength again. If over-fertilization occurs in a hydroponic system, the nutrient solution should be drained and replaced with a one-fourth or half strength solution. The gardener can then slowly increase the PPMs as the plants recover.
Cannabis plants require a specific blend of nutrients to thrive, just like any other living organism. When atmospheric conditions are optimal and the plants have everything they need, they can grow at an accelerated rate. However, when a nutrient deficiency or nutrient lock-out occurs, the ideal atmospheric conditions become irrelevant because the plant is unable to access the fuel it needs to complete the photosynthetic process. Cannabis growers who understand that the pH of the soil or nutrient solution is the most important contributing factor to nutrient absorption will be much more likely to have fewer nutrient related problems. Cannabis growers who understand the symptoms and early signs of common nutrient deficiencies will be armed with the knowledge needed to quickly resolve any issues that pop up and get back to doing what they love: growing healthy plants.
Eric Hopper is a Professional Marijuana Grower Senior Editor.