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Like any plant, cannabis requires certain growing conditions to remain healthy. It needs to have the right balance of nutrients to help in its development and for healthy growth.
As well as the key nutrients nitrogen, phosphorus, and potassium, magnesium is crucial in the life of a cannabis plant. Without magnesium, the plant will start to wither, cease to grow, and, you guessed it, eventually die.
If your plant has a magnesium deficiency, it’s “not the be all and end all,” however. There are certain signs and symptoms to look for so you can help rejuvenate the plant.
You can identify magnesium deficiency in marijuana quite easily. For instance, if it starts to grow yellow spots between the veins or on the edges of the leaves, but the leaves stay dark green, it probably lacks magnesium.
Although magnesium is considered a secondary nutrient in marijuana, the plant will not survive without it.
So, if you’re worried your cannabis plant is suffering from a deficiency of magnesium, read on. Today, we are going to talk you through what this looks like and the various ways to solve the problem.
No need to worry about your cannabis anymore! We’re here to help!
The Importance Of Magnesium In Cannabis Plants
It’s not just cannabis plants that require magnesium. All plants need this nutrient in order to develop and grow healthily.
The main reason magnesium is important is that it is crucial for photosynthesis to occur. Without this nutrient, the leaves would be unable to absorb light efficiently and process it into energy.
Magnesium is a key part of chlorophyll. Moreover, it aids in carrying phosphorus and phosphate metabolism, both key in the flowering stages of a plant.
This is why a plant with a deficiency of magnesium will inevitably starve to death, even with sufficient sunlight. But, this can be avoided with proper care and attention to your cannabis plant.
Symptoms Of A Magnesium Deficiency In Cannabis
It’s important to find the signs of magnesium deficiency in cannabis plants before it’s too late. In most cases, the symptoms will start on the lowest, oldest leaves.
Here, the first signs are a change in the color from dark green to a slight yellowing between the green veins.
Although magnesium deficiency can start in various parts of plants, the initial signs are typically on the tips of the leaves with marijuana.
This yellowish change in color then starts to move toward the base of the leaves. This is opposed to iron deficiency which tends to start at the base and then moves up.
Another sign is when the edges of the leaves feel slightly rough to touch. If they are a lighter green, have turned yellow, and/or are rough to feel, your plant is likely low on magnesium.
As the deficiency becomes worse, the yellowing will gradually start to rise. This process will see new shoots starting to grow a pale green color, whilst the petioles and stems start to turn a purple hue.
Those leaves that are most deficient will start to fold into themselves and soon die. Moreover, you may notice small brown spots on the leaves.
This is where the tissue has died, and the magnesium deficiency has gone too far.
So, here are the main symptoms summed up:
- The leaf color starts to grow yellow spots between its veins
- The leaf tips begin to die
- The edges of the leaves start to yellow
- The edges of the leaves start to curl in on themselves (usually upwards)
- The veins remain dark green
- The entire plant begins to lose its strength and its growth starts to slow
- Brown dots start to grow on the leaves
- The whole leaf starts to die
Solving A Problem Like Magnesium Deficiency
Most of the time, a sufficient amount of magnesium will be present in the soil surrounding a cannabis plant. But, the issue can often stem from the plant’s root system.
If this is the case, the cannabis plant will be unable to absorb magnesium effectively.
Root issues are the most common causes of magnesium deficiency in plants. Because of such a problem, it is not uncommon for symptoms of deficiencies regarding other nutrients to appear, too.
Simply adding more magnesium to the soil would not be helpful in this case. If you do this, the deficiency will not be solved and, in fact, it could create new issues and finish off the plant for good.
Below are the most important things to look out for to prevent magnesium deficiency in your cannabis plant or to help build up magnesium levels again.
Low Root Temperatures
Whether your cannabis plant prefers a warm or cold climate to grow properly, the temperature of the roots must be above 60 degrees Fahrenheit (16 degrees Celsius).
If the temperature goes below this, the roots will be unable to grow and function correctly.
If you’re growing your plants outdoors in pots, you should bring them inside during colder nights.
If you’re growing your cannabis plants indoors, we recommend utilizing a heater for grow tents. An electric blanket can also work well, as long as you set a timer on it.
If it’s not possible to move your pots, you should cover them.
You can do this with a tarp to prevent night dew from reaching your plants, or raise a greenhouse around the cannabis, though this will be more costly and hard work.
Low pH Level
You should inspect the pH level of the root zone. This should be one of, if not, the first steps when solving magnesium deficiency in marijuana plants.
If the pH level of the growth medium is found to be too low, it means it is very acidic. Therefore, the roots will not be able to absorb any magnesium.
The ideal pH level of the soil should be within the 6.0 to 7.0 range. This is when the roots can absorb magnesium best. If the pH is below 6.0, you will typically start to see issues.
Below 5.0 and the plant may die pretty quickly.
So, you know what you need to do – either increase or decrease the pH level to an appropriate amount. You can do this by using Dolomite Lime.
Dolomite can be purchased online and at nurseries or garden stores. It is a superb source of nutrients, combining magnesium and calcium.
Commonly used for commercial crops, dolomite has a neutral pH level of about 7.0. Therefore, it can help increase the pH variations in soil and maintain an optimal pH range for healthy cannabis growth.
This is especially useful on acidic substrates.
Apply dolomite by sprinkling a little on the substrate. It will then be absorbed slowly.
By applying dolomite, your cannabis plant can continue to thrive from the nutrients it provides over the next few months.
However, if you need to increase or decrease the magnesium immediately, this will not be the best fix.
For plants growing in pots, sprinkle around six tablespoons per four liters of the substrate over the ground.
If you’re growing your plant on soil, sprinkle a handful over the soil and around your plant.
Finally, water using standing water, so the lime and soil are moistened slightly. You can then start to water as you normally would the following day.
Moisture In Soil
If the soil around your cannabis plant is always wet, the magnesium could be getting blocked.
You must fix this problem to avoid potential root rot and for your plant to absorb magnesium properly.
Firstly, try not to water your plants too frequently. Instead, allow the soil to fully dry between each watering. To check, place about an inch of your finger into the soil to check if it has dried enough.
If your plant is being grown indoors, point a fan directly onto the soil. The moving air will help to dry the soil quickly.
Mineral Excess During The Flowering Phase
Whilst your cannabis plant is flowering and you’ve been adding some flowering fertilizer, you may notice some signs of magnesium deficiency.
If the plant absorbs too many minerals and nutrients, it may not be able to absorb magnesium properly.
If this occurs, you just need to flush the roots. Then, continue with the correct fertilizer for the current stage of growth.
Magnesium Supplements To Solve Magnesium Deficiency
As we mentioned above, certain supplements, such as Dolomite Lime, can be used to increase or decrease the amount of magnesium your marijuana plant is absorbing.
So, you have checked your plant and found:
- It has the right amount of fertilizer
- The correct pH level
- You are watering the roots at adequate times
- The root’s temperature is correct
If all of these bases are covered, you will need to supply magnesium with supplements.
Remember, if magnesium is being blacked, simply adding more will not solve the problem. It could make it worse.
Here are some magnesium supplements to consider using.
Also known as “magnesium sulfate,” Epsom salts can supply magnesium to your cannabis plants, either when mixed into the soil or via foliar application (this is when the leaves are sprayed with a solution).
Epsom salts can be used to correct sulfur deficiencies, as well as magnesium in plants.
Compared to some other magnesium additives, Epsom salts are more soluble, giving them an advantage. Because of this, foliar feeding becomes possible.
Here’s how to perform a foliar feed:
- To improve the solubility of the water, heat it up.
- Add one teaspoon of Epsom salt for every one liter of water.
- Wait for the water to return to room temperature.
- Spray the plant’s leaves completely with the solution. Spray underneath the leaves, too, but not so much that they are dripping with water in the end.
If you’re using a grow tent, you need to be very careful when foliar feeding. This is because the additional humidity can see fungi to form, and the plant can become ruined.
Moreover, do not wet the buds, as this can also be damaging to the plant.
The best time to spray your marijuana plant is when it gets dark. At this time, the temperature is usually cooler. Combined with darkness, these are the most favorable conditions for absorption, both indoors and outdoors.
If you spray your plant in the daylight, the water droplets can magnify the sun’s rays, leading to the danger of the leaves getting burned.
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If your plant has a magnesium deficiency, it probably has a calcium deficiency to boot. If this is the case with your cannabis, you can solve the issue with Cal-Mag, a calcium and magnesium supplement.
Apply during different stages of growth to supply your marijuana with the right amount of calcium and magnesium once again.
- CONTAINS MORE MICRONUTRIENTS THAN ANY OTHER BRAND: Iron (Fe), Zinc (Zn), Boron (B), Copper (Cu), Manganese (Mn), Molybdenum (Mo), Sulfur (S)
- BIOACTIVATED FORMULA FOR OPTIMAL NUTRIENT UPTAKE: Calcium and magnesium, Micro-chelated with fulvic acid; if you google it you’ll see why that’s good
- PREVENTS COMMON GROWTH DEFICIENCIES: Apply Cal-Mag in every stage of growth for strong stalk and leaf health. Apply with every watering for the full benefit
- COMPATIBLE WITH ANY NUTRIENT SYSTEM: 100% compatible with other nutrient systems, and can help make other minerals more bio-available
- CONTAINS NO HARMFUL EDTA: Unlike other brands, Bloom City uses organic chelates and never uses chemicals like EDTA, Healthier for your garden and healtier for the planet. We choose only the highest quality ingredient sources and manufacturing methods to create the world’s best craft growing nutrient systems
It’s important to tackle the early signs of magnesium deficiency in cannabis plants. By taking action with our various methods above, you can help your cannabis plant return to its magnesium glory days.
Once you have corrected the issue, the yellowing should cease after a few days.
Then, normal growth should resume, and new shoots should start to grow green and healthy again. If the leaves do not change, it means they may be irreparably damaged.
We hope this guide has helped you solve your magnesium deficiency in your marijuana plant so it can start to thrive once again.
I’m an avid gardener and cannabis enthusiast. You can usually find me in my garden caring for my plants or at my computer crafting helpful blogs for my readers.