Magnesium deficiency is a common problem for plants – and it has some nasty side effects. Luckily, there are ways to reverse the condition and save your plants.
So, how do you treat magnesium deficiency in plants? To treat magnesium deficiency in plants, spray the leaves with a solution containing magnesium (such as Epsom salt dissolved in water). To prevent the problem in the future, ensure proper watering and correct soil pH and magnesium levels.
Before you try these methods, make sure your plants really do have a magnesium deficiency. Otherwise, you are solving a problem you don’t have. In that case, you end up with too much magnesium – which also causes problems for your plants.
In this article, we’ll start off with an explanation of why magnesium is important for plants, along with symptoms and causes of magnesium deficiency. Then, we’ll go into a little more detail about how to add magnesium to your soil.
Let’s get going.
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Why Is Magnesium Important for Plants? (Why Do Plants Need Magnesium?)
Magnesium plays a key role in plant growth and development. According to the University of Minnesota Extension, magnesium (Mg) is the central atom in a chlorophyll molecule, as illustrated in the picture below.
Chlorophyll is what makes plants green. Chlorophyll is necessary for photosynthesis – a process where plants produce energy and oxygen from water, light, and carbon dioxide.
Magnesium also plays a role in carbohydrate metabolism. In simpler terms, this means that magnesium helps plants to use energy.
In addition, magnesium helps to carry phosphorus (a primary plant nutrient) through plant tissues.
According to the Mississippi State University Extension, magnesium is a secondary plant nutrient. This means that most plants need less magnesium than the primary NPK nutrients (nitrogen, phosphorus, or potassium).
However, magnesium is still an important nutrient – plants will suffer without enough of it.
In short, magnesium is essential for the survival of a plant. No magnesium means no chlorophyll, which means no photosynthesis, which means no energy, which means no plant growth!
(You can learn more about what magnesium does for plants in my article here).
Now that we know why magnesium is important, let’s look at some of the symptoms of magnesium deficiency.
Symptoms Of Magnesium Deficiency In Plants
If your plant is lacking magnesium, there are a few ways to tell. Check for the following symptoms to diagnose the problem:
You can read more about these symptoms below (or click on the links above to skip to the relevant section for each symptom).
*Note: some other nutrient deficiencies may appear with some of the same symptoms as magnesium deficiency. To tell for sure, you may need a soil test (more on this later).
Plant Magnesium Deficiency Symptom #1: Interveinal Chlorosis
Perhaps the most obvious symptom of magnesium deficiency is interveinal chlorosis. This is when the plant’s leaves turn yellow, but the veins stay green.
You can see the appearance of a leaf with interveinal chlorosis in the picture below.
The older leaves (which are found lower on the plant) tend to turn yellow first. This is because magnesium is a mobile nutrient, meaning that a plant can move the nutrient easily through its tissues.
When a plant suffers from a magnesium shortage, it takes magnesium from older leaves and sends it to the new leaves higher up on the plant. In essence, the plant is sacrificing the older leaves to ensure the health of the new leaves.
This makes sense because the upper leaves have a better chance to absorb sunlight. Also, it is better to have leaves higher up on the plant to avoid grazing by animal pests and competition from other plants.
According to the Montana State University, a magnesium deficiency will also cause the edges of the leaves to curl upward in some plants.
Some plants where magnesium deficiency is common include:
- Apples
- Currants
- Potatoes
- Raspberries
- Rhododendrons
- Tomatoes
Plant Magnesium Deficiency Symptom #2: Necrosis
According to the South Dakota State University Extension, a prolonged magnesium deficiency can progress from interveinal chlorosis to necrosis of leaves. Necrosis of leaves means that the plant cells are degenerating or dying off.
The tips and edges of the leaves will be affected by necrosis first. The leaves may turn purple in some areas – or they may simply fall off.
If your plant suffers from a severe magnesium deficiency, then you may see brown or black spots appear on the plant. The plant may also wilt or droop (it looks like the plant is tired, and would like to lie down and take a nap).
Plant Magnesium Deficiency Symptom #3: Stunted Growth
According to the University of Minnesota Extension, stunted growth is a classic symptom of magnesium deficiency. Remember: a lack of magnesium causes a lack of chlorophyll, which slows down photosynthesis, energy production, and growth.
The roots of a plant with stunted growth will be shorter than normal, and the shoots will be smaller than normal. The plant will also be more susceptible to disease.
If it does survive, you will notice a reduced yield for fruit and vegetables. This all goes back to lack of magnesium.
Without enough magnesium, plants cannot produce enough chlorophyll. Without enough chlorophyll, plants cannot manufacture enough energy to produce fruit, to grow, or even to survive.
Causes Of Magnesium Deficiency In Plants
There are many possible causes of magnesium deficiency in plants, including:
You can learn more about each of these causes below (you can click on the links above to skip to the relevant section).
Magnesium Deficiency Cause #1: Incorrect Soil pH
Every nutrient has an ideal soil pH range. Within this range, the nutrient is readily available for a plant to absorb through its roots.
In general, a good guideline for most plants is a soil pH of 6.0 to 7.0 (slightly acidic to neutral). However, some plants want more acidic soil – and each nutrient has its own ideal range for availability.
If your soil pH is too far below 5.5 (somewhat acidic), the magnesium in the soil will become less available for plants. Similarly, a soil pH that is too high will also make magnesium less available for plants.
For more information, check out this chart on Research Gate that illustrates nutrient availability by pH.
To find out what your soil pH is, buy a soil test kit online or from a garden center.
Make sure to test your pH and adjust it to a proper level before you add anything to treat a magnesium deficiency! To learn more, check out my article on testing your soil.
Note: adding lime to your soil will increase the pH. However, it also adds calcium to your soil, which can be a problem (more on that next).
Magnesium Deficiency Cause #2: Nutrient Imbalance
Gardening is all about balance – and I’m not trying to go all “Zen” on you. It’s true.
Not only do you need to have the right amount of each nutrient in your soil, but you also need to have the right ratios of nutrients – that is, achieve balance.
Basically, the potassium is “competing” with magnesium to be absorbed by the plant’s roots. To avoid this, make sure to use fertilizer without too much potassium.
Fertilizers are usually labelled with three numbers, representing NPK (nitrogen, phosphorus, and potassium) by weight.
For example, a 10-10-10 mix contains:
- 10% nitrogen by weight
- 10% phosphorus by weight
- 10% potassium by weight
Before you buy fertilizer, check the numbers on the bag and make sure the potassium content is not too high. For more information, check out my article about NPK ratios on fertilizer packages.
Similarly, excessive calcium can interfere with a plant’s ability to absorb magnesium. Adding bone meal or lime to your soil increases calcium levels, so be careful about adding too much of these at one time.
To read more about how excess calcium or potassium can affect magnesium availability, check out this article on Science Direct.
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Magnesium Deficiency Cause #3: Poor Soil Conditions
According to the Michigan State University Extension, poor soil conditions can cause a magnesium deficiency. This includes sandy soil or cold and wet soil caused by inclement weather conditions.
For example, heavy rainfall leaches magnesium out of the soil, carrying it away so that your soil becomes deficient.
Cold soil also decreases a plant’s ability to absorb magnesium. If you plant too early in the year, when the soil is still cold, you may encounter this problem.
A late frost or a prolonged period of unseasonably cold weather will cause the same problem.
Finally, sandy and acidic soil also cause magnesium deficiency in plants. According to the Iowa State University Extension:
“Magnesium deficiency is favored by very acid, sandy soils in regions of moderate to high rainfall where magnesium has been extensively leached from the soil profile.”
https://crops.extension.iastate.edu/files/article/nutrientdeficiency.pdf
Magnesium Deficiency Cause #4: Lack of Magnesium in Soil
If none of the above conditions apply to your garden, then you may in fact have a lack of magnesium in your soil. This can happen for a couple of different reasons.
One possible explanation is that there was never enough magnesium in the soil to begin with.
Another possibility is that there was magnesium in your soil at one point, but it has since been depleted by farming, gardening, runoff from rainfall, etc.
A deficiency of magnesium (or other nutrients) can occur if you plant the same crop in the same place in your garden every year. To avoid some of this depletion, use crop rotation (plant a crop in different parts of your garden each year).
How Do You Test For Magnesium Deficiency In Soil?
No matter what causes a magnesium deficiency in your soil, you will want to know how severe the problem is. That way, you’ll know how to treat the problem.
The best way to find out is to use a soil test kit, which you can buy at a garden center or online. A soil test kit can tell you the levels of magnesium and other nutrients in your soil.
If you want a more precise test conducted by an expert, you can send a soil sample to your local agricultural extension office. If you tell them what you are growing, they may be able to offer recommendations on how to treat your soil.
You can learn more about how to do a soil test in my article here.
Magnesium Deficiency Cause #5: Improper Watering
Watering too much (or not enough) can also lead to magnesium deficiency in plants.
Plants need some water in the soil so they can absorb nutrients. After magnesium dissolves in water, plants can absorb the magnesium solution from the soil through their roots.
In dry soil, plants cannot absorb magnesium. This leads to yellow leaves, along with other nutrient deficiency symptoms.
Likewise, if you water too much, you can also cause problems. For one thing, root rot is more likely when roots stay too wet for too long (and cannot get enough air).
Without healthy roots, a plant will not be able to absorb magnesium – even if there is plenty of water and magnesium in the soil.
To avoid watering problems, keep an eye on the soil around plants. Feel the soil with your fingers, at a depth of a few inches. If it feels dry, water – if it is damp, hold off on watering.
What Is A Good Source Of Magnesium For Plants? (How To Add Magnesium To Soil)
If you are reading this, then you have decided that the magnesium levels in your soil are low. Luckily, there are a few ways to give your plants the magnesium they need, including:
- Epsom Salt (magnesium sulfate)
- Dolomite Lime
- Sulfate of Potash Magnesia
- Compost Or Manure
- Fertilizer
Some of these sources add magnesium to the soil, and others add it directly to the plant, but both methods will work.
Plant Magnesium Source #1: Epsom Salt (magnesium sulfate)
Maybe you have not planted anything yet, but a soil test shows a magnesium deficiency. Or, maybe you saw signs of magnesium deficiency in last year’s crop, and you want to avoid the same problem this year.
Either way, you can use Epsom salt to help address the problem.
How To Add Epsom Salt To Soil
To treat a magnesium deficiency in your soil, add some Epsom salt (magnesium sulfate), along with any other fertilizers you use (such as compost, manure, etc.)
To add magnesium before planting, use a shovel to turn the mixture into the soil and blend it in evenly. Then, plant your seeds or move your transplants into the improved soil.
If you have already planted this year and your plants are showing signs of magnesium deficiency, don’t worry. You can also make a spray to treat your plants directly on their leaves.
How To Use Epsom Salt As A Foliar Spray
First, add one tablespoon of Epsom salt to one gallon of water. Mix them together thoroughly until the salt is completely dissolved.
Next, pour some Epsom salt water solution from the gallon into a spray bottle.
Then, spray the leaves of the plants suffering from magnesium deficiency. This is known as foliar feeding, and the plant will absorb the solution directly through its leaves.
Note: regardless of which method you use, be careful about adding too much Epsom salt all at once! Although it can be helpful for curing magnesium deficiency, it is not a cure-all to be whipped out for any and all reasons.
(For more information, check out my article on Epsom salt for growing tomatoes).
Plant Magnesium Source #2: Dolomite Lime
Dolomite lime (or dolomitic limestone) is another source of magnesium for your soil to help cure a deficiency. Dolomitic lime (or calcium magnesium carbonate) is a type of natural limestone.
Dolomitic limestone will supplement both calcium and magnesium. This is helpful if a soil test indicates that your soil lacks both of these nutrients.
Plant Magnesium Source #3: Sulfate Of Potash Magnesia
Sulfate of Potash Magnesia (also called Sul-Po-Mag or K-Mag) is another soil supplement that can provide magnesium if your garden is lacking.
This supplement also provides sulfur and potassium, which is helpful if one or both of these other nutrients are also deficient in your soil.
Plant Magnesium Source #4: Compost or Manure
You can create your own mix to maintain magnesium and other nutrient levels in your garden. Adding leaves, grass clippings, and food scraps (not meat!) to your compost pile will help to restore these nutrients to the soil.
As long as your leaves and grass are not magnesium deficient, this method should help to keep magnesium levels stable. At the very least, it will allow you to use a little bit less of the magnesium supplements mentioned earlier.
Healthy garden soil should always start with natural supplements, such as compost or manure. These will restore nutrients to the soil and replace organic material in the soil, which improves drainage.
For more information, check out my article on how to make your own compost.
Plant Magnesium Source #5: Fertilizer
You can also choose a fertilizer off the shelf at the store, as long as it has some magnesium included in the mix. However, remember to consider the nutrient imbalances we talked about earlier.
Also, be careful about adding fertilizer with high potassium or calcium levels, since these nutrients can interfere with a plant’s uptake of magnesium.
Finally, be careful about over fertilizing. After all, too much of a good thing can cause a bad thing, such burning your plants with too much nitrogen.
(For more information, check out my article on over fertilizing).
What Does Too Much Magnesium Do To Plants? (Excessive Magnesium)
With all this talk about magnesium deficiency, it seems impossible to have too much magnesium in your garden soil. However, it can happen!
If you add too much magnesium-rich fertilizer without testing your soil, you can end up with excessive magnesium levels in your soil.
For this reason, take my advice and check your pH (and other nutrient levels) before adding magnesium to your soil. Add a small amount at first – you can always add more later, but you can’t go back after you add too much!
Remember what we talked about earlier with regards to the balance between different nutrients. Too much magnesium will turn the tables and inhibit a plant’s ability to absorb calcium and potassium.
This, in turn, will lead to other nutrient deficiencies, inhibiting growth and harming plant health.
Conclusion
At this point, you have a good idea of how to identify magnesium deficiency and what the cause may be. Hopefully you also know how to solve the problem, and how to prevent it in the future.
You might also want to read my article on what magnesium does for plants.
I hope this article was helpful – if so, please share it with someone who can use the information.
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~Jonathon