Causes of Magnesium Deficiency in Plants (Plus 5 Ways to Fix It)


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?  One way to treat magnesium deficiency in a plant is to spray the leaves of the plant with a solution containing magnesium, such as Epsom salt dissolved in water.  Another method is to mix compost, Epsom salt, or another magnesium source directly into the soil.

Before you go and try these methods, it is important to make sure that your plants really do have a magnesium deficiency.  Otherwise, you could end up with too much magnesium, which can also cause problems for your plant.

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.

Why is Magnesium Important for Plants? (Why Plants Need Magnesium)

For one thing, 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 molecule
A chlorophyll molecule – note the central magnesium (Mg) atom.

Chlorophyll is what makes plants green.  Chlorophyll is also 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 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!

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.

*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, where 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.

interveinal chlorosis
Leaves displaying interveinal chlorosis – the veins are green, but the space between is yellow.

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 plants 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, especially since leaves that are higher up on the plant have a better chance of catching and absorbing sunlight. Also, it is better to have leaves higher up on the plant, considering both the threat of grazing 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
Magnesium deficiency is common in apple trees.

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.

leaf necrosis
Leaf necrosis is a common symptom of magnesium deficiency in plants.

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.

tomato plant roots
A plant without enough magnesium will suffer from stunted growth, including shorter roots.

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.  Some of them can cause a problem even when there is plenty of magnesium in the soil.

Magnesium Deficiency Cause #1: Incorrect Soil pH

Every nutrient, including magnesium, has an ideal soil pH range where the nutrient is readily available for plants to absorb through their roots.  In general, a good guideline for most plants is a soil pH of 6.0 to 7.0 (slightly acidic to neutral).

If your soil pH is too far below 5.5 (somewhat acidic), the magnesium in the soil will start to become less available for uptake by your plants.  Similarly, a soil pH that is too high will also make magnesium less available for your 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, you should buy a soil test kit online or from a garden center.

soil test kit
A soil test kit will tell you if there is a deficiency of magnesium or other nutrients in your soil.

Make sure to test your pH and adjust it to a proper level before you add supplements and fertilizers for a magnesium deficiency! To learn more, check out my article on testing your soil.

Note: adding lime to your soil will increase the pH, but 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 (i.e. balance).

For example, according to the Iowa Statue University Extension, high levels of potassium can interfere with a plant’s ability to absorb magnesium.

Basically, the potassium is “competing” with magnesium to be absorbed by the plant’s roots. To avoid this, make sure to use fertilizer without excessive potassium.

Fertilizers are usually labelled with three numbers, representing NPK (nitrogen, phosphorus, and potassium) by weight.  For instance, a 10-10-10 mix contains 10% nitrogen, 10% phosphorus, and 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 will increase 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.

Magnesium Deficiency Cause #3: Poor Soil Conditions

According to the Michigan State University Extension, poor soil conditions can cause a magnesium deficiency. This includes cold, wet, and sandy soil caused by inclement weather conditions.

For example, heavy rainfall may leach magnesium out of the soil, carrying it away so that your soil becomes deficient.

dry soil
This is definitely poor soil – and yet something is still growing in it!

Cold soil will also decrease 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 could cause the same problem.

Finally, sandy and acidic soil can 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.”

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.

rain
Heavy rainfall can cause magnesium and other nutrients to leach out of certain soils.

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.

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.

Some of these sources add magnesium to the soil, and others add itdirectly to the plant, but both methods will work.

Plant Magnesium Source #1: Epsom Salt (magnesium sulfate)

Maybe you have not planted anything in your garden yet, but a soil test showed a magnesium deficiency.  Or, maybe you saw signs of magnesium deficiency in last year’s crop, and 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.

magnesium sulfate
Epsom salt (magnesium sulfate) provides magnesium for plants, either by adding to soil or spraying on the leaves after dissolving in water.

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 by 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.

spray bottle head
Use a spray bottle to apply an Epsom salt solution in water to the leaves of plants (foliar feeding).

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 lime) 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.

compost
With a little more time, this compost will be ready for the garden.

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.

ammonium nitrate
Fertilizer can help to provide nutrients for your plants, but don’t use too much at once or you will burn them! Follow the instructions on the package.

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 the growth and harming the health of your plants.

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.

If you want to read some of my most popular posts, check out the “Best of GreenUpSide” page here.  Enjoy!

~Jonathon

jonathon.david.madore

Hi, I'm Jon. Let's solve your gardening problems, spend more time growing, and get the best harvest every year!

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