Magnesium deficiency is one of the most common nutrient issues faced by cannabis growers. Left unchecked, it can quickly spiral out of control, causing extensive leaf yellowing, loss, and sickly plants.
Fortunately, magnesium deficiencies are easy to correct when caught early This article provides a complete guide to identifying, treating, and preventing magnesium deficiencies in your cannabis garden
What Causes Magnesium Deficiency in Cannabis Plants?
Magnesium (Mg) is an essential macronutrient for cannabis. It plays a crucial role in chlorophyll production, photosynthesis, enzyme functions, and other plant processes.
Several factors can cause magnesium deficiency in cannabis plants
- Low magnesium levels in soil or growing medium
- Using pure water sources like reverse osmosis or distilled water
- Improper pH affecting magnesium absorption
- Calcium supplements without added magnesium
- Overwatering or poor drainage
Magnesium gets locked out when grow medium pH drifts too low. For soil aim for 6.0-7.0, for hydro 5.5-6.5. Even with adequate magnesium, inappropriate pH prevents absorption by the roots.
Identifying Magnesium Deficiency in Cannabis
The most common visual sign of magnesium deficiency is interveinal chlorosis – yellowing between the veins, especially on older, lower leaves. This happens because magnesium is mobile in the plant, so deficiencies start on less important growth.
Other symptoms include:
- Leaves feeling brittle or crispy
- Brown spotting on leaves
- Purple stems and petioles
- Slow growth
- Smaller yields
Without enough magnesium, leaves lose chlorophyll and the ability to photosynthesize optimally. The deficiency spreads upwards gradually, eventually affecting the whole plant if not corrected.
How to Treat Magnesium Deficiency in Cannabis Plants
Treating magnesium deficiency requires a multi-pronged approach:
1. Check and adjust pH – Test pH of soil or reservoir and adjust to 6.0-7.0 for soil, 5.5-6.5 in hydro. This maximizes magnesium absorption.
2. Flush grow medium – Flush with pH adjusted water to remove any nutrient buildup.
3. Add magnesium supplement – Add 1-2 tsp/gallon of magnesium supplement like Epsom salts or CalMag. Can foliar feed for faster absorption.
4. Monitor recovery – New growth should appear healthy within a week. If not, continue adding magnesium until deficiency clears.
5. Remove damaged leaves – Prune away heavily affected leaves to reduce stress on the plant.
The key is catching deficiencies early before they spread too far. A quick magnesium boost along with proper pH solves most cases.
Preventing Magnesium Deficiency in Cannabis
Prevention is the best cure when it comes to plant nutrition. Here are some tips to avoid magnesium issues:
- Test soil/water magnesium levels before planting
- Use dolomite lime or Mg-rich amendments in soil
- Choose complete hydroponic nutrients with magnesium
- Supplement tap water with CalMag
- Maintain proper pH for maximum nutrient absorption
- Avoid overwatering which can leach magnesium
- Monitor plants for early deficiency signs
Giving your cannabis adequate magnesium right from the start provides lush green growth. Combined with vigilant monitoring and early treatment, deficiencies don’t stand a chance!
Magnesium’s Vital Role in Cannabis Growth
Why is magnesium so important for cannabis plants? Let’s take a closer look:
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Chlorophyll production – Magnesium is the central atom in chlorophyll molecules responsible for photosynthesis.
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Enzyme functions – Magnesium helps activate hundreds of vital plant enzymes.
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ATP synthesis – Magnesium aids production of adenosine triphosphate which transports energy within the plant.
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Cell growth – Magnesium deficiency impairs proper cell division and growth.
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Nutrient absorption – Magnesium helps plants take up key nutrients like phosphorus.
By ensuring an adequate magnesium supply, your cannabis plants can reach their full genetic potential in terms of growth, potency, and yield.
Frequently Asked Questions About Magnesium Deficiency
Here are answers to some common questions about magnesium deficiencies:
What causes magnesium deficiency in cannabis?
Low levels of magnesium in the growing medium, inappropriate pH, pure water sources, and overwatering are the most common causes.
What are the signs of magnesium deficiency?
Interveinal leaf yellowing, leaf margins browning and feeling crispy, purple petioles, and slowed growth.
How can I fix a magnesium deficiency organically?
Epsom salts or dolomite lime are good organic magnesium amendments. 1-2 tsp per gallon of Epsom salts makes a good foliar spray.
When should I add magnesium to my plants?
Add magnesium supplements or amendments when planting, when deficiency signs appear, when switching to flowering, and any time plants show increased demand.
How often should magnesium be added to plants?
Ideally maintain a constant supply instead of heavy periodic additions. Check soil/leaf levels and add magnesium anytime they dip low.
What is the best magnesium supplement?
For hydroponics, CalMag or magnesium sulfate (Epsom salts) work very well. In soil, use dolomitic lime for slower release magnesium.
How much magnesium does cannabis need?
Commercial cannabis cultivation research indicates ideal magnesium levels around 0.5% – 1.5% in leaf tissue samples.
Conclusion
Magnesium deficiency is a common problem faced by cannabis growers. The good news is it can be readily prevented and corrected when caught early.
Follow the tips in this guide to meet your plants’ magnesium needs for lush green growth and impressive yields!
How can magnesium deficiency in cannabis plants be identified?
As the primary ‘building block’ of chlorophyll, magnesium is what gives it, and therefore the plant itself, a healthy bright green colour. The first and most easy to identify sign of magnesium deficiency in cannabis plants is the leaves showing a worrying fade of green to pale green to yellow.
This is known as chlorosis. Although there are other problems that also cause chlorosis, magnesium deficiency in cannabis shows up first around the edges and in between the veins on the leaves, rather than all over them or from the stems outwards or tips inwards.
The first leaves to show these signs will be the oldest ones, and the ones closest to the bottom of the plant (often, these are the same ones). This is caused by the plant withdrawing magnesium from these leaves in order to send it to the newer ones, in an effort to keep itself alive (in much the same way as the human body pulls blood away from the extremities in cold weather to keep the vital organs warm).
The leaves might also start to feel crunchy and dry, although it is not advisable to wait until this happens before starting treatment!
What causes magnesium deficiency in cannabis plants?
Unsurprisingly, the first culprit is not enough magnesium in the soil. It is an unfortunate fact that magnesium can be quite easily washed away by flushing or overwatering. The good news is that depending on where you live, your tap water may actually contain useful levels of magnesium!
Even if there are sufficient levels of magnesium in the soil, the plant may not be able to make use of them. A substrate with a pH value that is too low, i.e. very acidic, prevents the roots from absorbing magnesium even if it is plentiful. It is also important to know that adding more magnesium to a substrate that already has enough can make the situation worse.
Other necessary nutrients can be ‘locked out’ by an excess of magnesium in the substrate, and suddenly the gardener has multiple nutrient deficiencies to deal with, not just one!