Iron Deficiency in Plants & How to Add Iron to Garden Soil


The other day, I noticed that the top leaves of some of my houseplants were turning yellow.  I did some research, and sure enough, this is a good indicator of iron deficiency.  I decided to do some research to find out ways to add iron to soil.

So, how do you add iron to garden soil?  You can add chelated iron powder or blood meal directly to the soil to add iron.  You can also add fertilizer or your own compost, as long as the iron content is high enough.  Another option is to add chelated iron or iron sulfate in liquid form by spraying the leaves of the plant.

Before you go adding supplements and fertilizers to your soil, it is a good idea to make sure that you really do need more iron in your garden.  Let’s start by taking a look at the role of iron in plants, along with the symptoms of iron deficiency.  That way, you can tell if your plants are suffering from iron deficiency.

Then, we’ll talk about the causes of iron deficiency, and how you can solve the problem in each case.  Finally, we’ll talk about ways to add iron to your soil or directly to your plants.

Why is Iron Important for Plants?

Iron serves several important functions in plants.  First of all, iron is involved in the production of chlorophyll through photosynthesis.  Remember: chlorophyll is the compound that makes plants green.

green lettuce
This lettuce has plenty of iron.

Iron is also important in plant respiration, which is when plants use sugar (from photosynthesis) and oxygen to produce energy for growth.

In addition, iron plays a role in the transport of nutrients, such as oxygen, throughout a plant’s tissues. 

In short, iron is vital to the overall health and development of plants.  A deficiency will interfere with all of the processes mentioned above.  Now let’s talk about how to tell that a plant has an iron deficiency.

Symptoms of Iron Deficiency in Plants

Once you know what to look out for, you can identify the problem when it occurs, and take appropriate steps to solve the problem.  Here are a few of the telling symptoms of iron deficiency in plants.

Iron Chlorosis

One of the most obvious symptoms of iron deficiency in a plant is iron chlorosis.  You will see the top leaves of the plant turn yellow first, and then the lower leaves will follow.

However, the veins of the leaves will remain green.  This appearance (yellow leaves with green veins) is called interveinal chlorosis.

interveinal chlorosis
This leaf is suffering from iron deficiency.

The newer leaves on the plant are affected first because iron is an immobile nutrient.  This means that a plant cannot easily move iron throughout its tissues.

Thus, the older, more established leaves keep their iron and stay green for a while, while new leaves quickly turn yellow due to lack of iron.

Poor Growth

A plant suffering from iron deficiency may also show signs of poor growth.  Such a plant may look smaller than the others in your garden.  It won’t grow as tall, and it won’t grow as quickly.  This is because iron deficiency disrupts plant respiration and nutrient transport.

Small Flowers or Lack of Fruit

Finally, an iron deficiency may cause a plant to produce small flowers, along with small fruit and less fruit than other healthy plants.  Since iron is involved in photosynthesis, a lack of iron affects a plant’s ability to create and use sugar for energy or to produce flowers and fruit.

Causes of Iron Deficiency in Plants

Now that you know that iron deficiency looks like in plants, it’s time to figure out why it happens.  Some of the reasons may surprise you!

High pH (Alkaline Soil)

If the pH of your soil is too high, then your plants can end up with an iron deficiency – even if there is plenty of iron in the soil!  How can this happen?

For every nutrient that a plant needs, including iron, there is an ideal pH range for the soil.  Within this range, the nutrient is highly available, and the plant can easily absorb the nutrient through its roots.

Outside of this range, the nutrient is not available, and so the plant cannot absorb enough of the nutrient, even if it is present in the soil.

As a general rule, you will want to keep your soil pH between 5.5 and 6.5 (slightly acidic) for most plants.  More specifically, iron is highly available in acidic soil (pH below 7).

However, as pH rises to 8 or higher, iron becomes less available in the soil.  For more information, check out this chart from Research Gate that gives you nutrient availability based on pH.

Plants that like acidic soil, such as raspberries, blueberries, pears, and azaleas, are more likely to get iron chlorosis.

blueberries
Blueberries like acidic soil.

The moral of the story is to check your soil pH before you add iron supplements or fertilizers.  The problem may be your pH, and adding iron when there is no need can lead to iron toxicity (more on this later).

If you want to check your pH, buy a pH test kit at a garden center or online. For more information, see my article on how to test your soil.

If you need to make your soil more acidic, you can add sulfur. For more information, check out my article on how to make your soil more acidic.

Nutrient Imbalance

This is another tricky problem that can cause iron deficiency in your plants, even when there is plenty of iron in the soil and the pH is in the proper range.

Remember that gardening is all about balance.  In addition to having enough of each nutrient in the soil, you need to have the proper ratios for each nutrient.

Too much of one nutrient can block a plant from absorbing another.  For example, excessive amounts of phosphorus can prevent iron uptake in a plant.  This can occur if you use a garden fertilizer with high phosphorus content.

If you’re not sure, check the three numbers on a fertilizer package: they represent N-P-K, or percentage by weight of nitrogen, phosphorus, and potassium.  The middle number represents phosphorus –  for more information, check out my article explaining the numbers on a fertilizer package. If you think phosphorus is too high, find a fertilizer with lower (or zero) phosphorus content.

Likewise, excess calcium can prevent iron uptake in a plant.  This can occur in soil with high lime content (lime is just another word for certain calcium compounds).  Be careful about adding lime to your garden as a supplement if you suspect iron deficiency in your plants.

Poor Soil

If your soil is too wet or too tightly packed, there will not be enough air for iron uptake.  This can also happen if you use plastic to cover the ground around plants to prevent weeds.  Cold soil can also inhibit iron uptake in your plant.

If your soil is more like clay, you may want to add some organic material, such as peat moss or your own compost made from leaves, grass clippings, and other organic matter (banana peels, coffee grounds, etc.) For more information, check out my article on how to make your own compost.

Extreme Conditions

Extreme weather conditions can also cause iron deficiency in plants.  High temperatures or intense sunlight can disrupt a plant’s uptake of iron.

As with pH, there is a certain ideal range for temperature.  Outside of this range, the plant will start to suffer.  The same is true for sunlight, in terms of both duration and intensity.

Insufficient Iron in Soil

If none of the above conditions apply to your garden, then your soil may contain insufficient iron for your plants.  This can occur for a couple of different reasons.  One possible explanation is that there was never enough iron in the soil to begin with.

Another possibility is that the iron that was in your soil has been depleted.  This can happen if you plant the same iron-hungry 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).

Whatever the cause of iron deficient soil, you will want to know for sure if this is the problem, and how severe it is.  The best way to find out is to use a soil test kit, which you can buy at a garden center or online.

In addition to iron levels, a soil test kit can tell you the levels of other nutrients in your soil.

How to Add Iron to Garden Soil

If you are reading this far, it means that you are confident that your soil has a low iron content.  Here are a few ways that you can add iron content to your garden soil.

Chelated Iron

As you may have guessed, simply adding pure elemental iron to your garden may not help with an iron deficiency in the soil.  The iron must be in a form that will be available to plants.

One such form is chelated iron, which comes in powder and liquid forms.  You can mix the powder directly into the soil for a more long-term fix.  Alternatively, you can spray the leaves with the liquid form if there is imminent danger of losing a plant with an iron deficiency.

Iron Sulfate

Iron sulfate is another form of iron that is available to plants.  You can spray the liquid form on the leaves of the plant.  An added benefit is that iron sulfate also supplies sulfur to plants, which is another necessary nutrient.

Blood Meal

Blood meal is made from dried and powdered blood from slaughterhouses.  As with chelated iron powder, you can mix it directly into the soil.  Blood meal does supply some iron to the soil, but it is also high in nitrogen.

So, make sure that you don’t end up with excessive nitrogen. This is probably difficult to do, since plants use up tons of nitrogen in the vegetative stage as they grow to maturity. Nevertheless, it can happen – if you are concerned, check out my article on low-nitrogen fertilizers.

Compost High in Iron

You can make your own compost from leaves, food scraps (not meat!), and grass clippings.  As long as your leaves and grass are not iron deficient, your finished compost should contain plenty of iron for your plants.

compost bin
This mix will do well in your garden, after it breaks down into compost.

Fertilizer High in Iron

You can choose a fertilizer off the shelf that will specifically supplement iron. However, these fertilizers will also contain other nutrients, which could be a problem.

Remember what we talked about earlier: excessive phosphorus or calcium can block a plant’s uptake of iron from the soil.  You don’t want to add iron and then prevent the plant from absorbing it!

A Few Words About Excessive Iron

After all this talk of iron deficiency, it must seem impossible to have too much iron in your soil.  However, it can happen, especially if you add iron without checking for other problems (pH level or levels of other nutrients).  High levels of iron can cause manganese deficiency and disrupt photosynthesis.

Conclusion

By now, you have a good idea of whether your plants are suffering from iron deficiency, and what could be causing the problem.  It’s time to get out into the garden and do some detective work to solve the problem!

I hope this article was helpful.  If you have any questions, please leave them in the comments below.

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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