Magnesium is an essential nutrient for healthy cannabis growth. A lack of magnesium causes the plant to lose its ability to produce chlorophyll, leading to yellowing leaves and sickly plants. Left unchecked, a magnesium deficiency can quickly spiral out of control. Luckily, magnesium deficiencies are easy to treat if caught early. This article covers how to identify, prevent and treat magnesium deficiency in cannabis.
What Causes Magnesium Deficiency in Cannabis?
Magnesium deficiency is one of the most common nutrient deficiencies in cannabis plants The main causes include
- Low levels of magnesium in the growing medium or water supply (common with RO water, coco coir, or very acidic soil)
- Incorrect pH levels prevent the plant from absorbing magnesium properly
- Using calcium supplements without adding magnesium
Identifying Magnesium Deficiency
The most common signs of magnesium deficiency in cannabis are:
- Yellowing of leaf margins and veins, especially on lower/older leaves
- Leaves may start feeling crispy or brittle
- Purple stems
- Slowed growth
Magnesium is mobile within the plant, so the deficiency usually starts on the lower, older growth. Without enough magnesium to produce chlorophyll, the leaves lose their green color and eventually die and fall off.
As the deficiency worsens it spreads up the plant to younger leaves. Advanced magnesium deficiency causes extensive yellowing browning, and leaf loss.
Preventing Magnesium Deficiency
The best way to prevent magnesium deficiency is to ensure your plants get sufficient magnesium right from the start.
- When planting in soil, mix in a magnesium-rich amendment like dolomite lime
- Use a complete hydroponic nutrient formula that contains magnesium
- If using RO or filtered water, add a calcium-magnesium supplement
- Maintain a pH between 6.0-7.0 to maximize magnesium absorption
Treating Magnesium Deficient Cannabis Plants
If you catch a magnesium deficiency early it can usually be reversed. Here’s a step-by-step guide
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Flush grow medium – Flush the growing medium with pH’ed water to remove any nutrient buildup.
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Check pH – Check that the pH is within the ideal range. Adjust pH if needed.
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Add magnesium – Add a magnesium supplement like CalMag or Epsom salts. Follow label directions.
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Monitor growth – The deficiency should stop spreading within a few days. Watch new growth for signs of recovery.
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Adjust as needed – If the problem persists, continue adding extra magnesium until new growth looks healthy.
The damaged leaves likely won’t recover, but new growth will appear lush and green again once the deficiency is corrected. It’s essential to catch magnesium issues early before they have a chance to spiral out of control.
Magnesium Deficiency in Soil Grows
For soil grows, flushing with 6.5 pH water will help reset the soil and make magnesium available again. Then mix 1-2 teaspoons of Epsom salts per gallon of water and use that to water plants. This provides a quick magnesium boost.
You can also mix dolomite lime into soil at planting time as a slow-release magnesium source. Use 6-7 teaspoons per gallon of soil. Dolomite lime maintains proper pH and provides calcium too.
Fixing Magnesium Deficiency in Hydro & Coco
In hydroponic systems, check that the reservoir water is within the ideal pH range for your growing medium. For hydro, maintain a pH between 5.5-6.5. In coco coir aim for 5.8-6.2.
Adding a calcium-magnesium supplement like General Hydroponics CaliMagic or Botanicare Cal-Mag will quickly treat a magnesium deficiency. Use 1-2 tsp per gallon of nutrient water.
Give Your Plants the Magnesium They Need
While magnesium deficiency can be frustrating, it’s easily avoidable. Maintain proper pH, use a complete nutrient formula, and supplement with magnesium at the first signs of trouble. With the right remedy, your plants will be back to vigorous green growth in no time!
The effect of light quality and intensity
Even if the plants are fed a nutrient solution with all the macro and micronutrients they need and are carefully watched and given the right amount of nutrients, magnesium deficiency can still happen. Cannabis plants can lose magnesium for a number of reasons, such as when the pH level is off, nutrients are locked out, or the environment is too stressful.
Furthermore, according to Ryan, both light quality and intensity can have an influence on nutrients. He talked about a very specific problem that growers have to deal with all the time: “An HPS has a lot of yellow and orange light in that spectrum, and the infrared can damage the proteins in your plant.” These are clearly essential for e. g. , transferring all the photosynthetic production within the plant. Damage to these proteins causes early yellowing, which makes growers think the plants don’t have enough nitrogen, calcium, or magnesium.
It is important to know that magnesium (Mg2), calcium (Ca2), and potassium (K) are all cations, which means they are positively charged. e. , positively charged ions). So, the balance between them is very important, not only to avoid deficiencies but also to keep them from competing with or harming other nutrients in the root zone. But this has something else to it, says Ryan. It is not about adding more nutrients and adapting the EC. “If a farmer checks the Mg level in the leaves before adding these extra nutrients, they will see that it is just right.” But this is where it gets tricky with this nutrient. When a plant’s roots feel like they need a little more magnesium, it stores it in the leaf. So which is it—a lack of something or a way to protect itself? That’s why growers usually just add something extra that gives them calcium and magnesium; their calcium levels are probably fine. ”.
Ryan talked about this case with HPS lamps and emphasized that growers who switch to LEDs will need to get to know their plants better because the infrared isn’t as strong with LEDs.
That being said, Ryan ended our meeting by saying, “The best advice I can give is to draw more conclusions from data and know your plants and technology.” Even in this case, doing a leaf analysis and being able to read and understand it. Anyone who grows crops and pays attention to these things will be able to tell when something goes wrong with their crops and know what to do about it.
The importance of magnesium
According to Ryan, the most common nutrient deficiency for cannabis in high-light conditions is magnesium, and this is often affected by the type of light. He went on to explain his point of view. Let’s take a quick look at what magnesium does and how important it is. Magnesium is an essential macronutrient for cannabis plants and they need a lot of it to grow and develop properly. Among its many functions, Mg is crucial for photosynthesis, as well as in the synthesis of chlorophyll.
Cannabis plants can show different signs of magnesium deficiency depending on how bad the deficiency is and what stage of growth the plant is in. See the figures below for illustration. Generally, the signs include the yellowing or browning of older leaves. In severe cases, leaves may become necrotic and eventually fall off the plant. Additionally, the plant may exhibit stunted growth, reduced yields, and poor bud development.
Quick Visual Guide to Nutrient Deficiencies in Cannabis
FAQ
How to fix magnesium deficiency in plants?
How do you add magnesium to a pot plant?
Can overwatering cause magnesium deficiency?
What is a good source of magnesium for plants?
Why does my cannabis plant have a magnesium deficiency?
Incorrect watering routine is perhaps the second most common reason why cannabis plants face magnesium deficiency. Fortunately, if you are using tap water, this likely won’t be the cause of your plant’s magnesium deficiency because tap water in most regions is rich in magnesium. 3. Low pH in the Grow Medium
Is it possible to have too much magnesium?
In general, excess magnesium occurs through the consumption of supplements, and can cause intestinal and stomach symptoms, even cardiac arrest. To have adequate levels, the varied consumption of fruits and vegetables is recommended.
Why does my plant have a magnesium deficiency?
Fortunately, if you are using tap water, this likely won’t be the cause of your plant’s magnesium deficiency because tap water in most regions is rich in magnesium. 3. Low pH in the Grow Medium pH is a small detail that can have a drastic impact on your plant’s growth, specifically, how it absorbs nutrients.
How do you know if a plant has a magnesium deficiency?
The plant will pull magnesium out of older leaves and bring them to the newer leaves. That’s why a magnesium deficiency usually appears towards the bottom of the plant and on older, less important leaves. The edges of the leaves may become yellow or bright green and may start feeling crispy to the touch.
Why do cannabis plants need magnesium?
The reason that plants – and not just cannabis plants – need magnesium is simple: it is essential for photosynthesis. Without it, leaves cannot absorb and process light into energy. Plants with magnesium deficiency will eventually starve to death, even if they are getting the correct amount of hours of light.
What are the signs of cannabis magnesium deficiency?
The stems of cannabis plants turn reddish-purple when they are deficient in magnesium. One of the signs of cannabis magnesium deficiency is abnormal growth. With magnesium deficiency, the leaves will start to have abnormal growth. It can impair the cannabis plant’s health and lower yields if left unchecked.