An iron deficiency in plants is recognized by yellowing leaves (there are other common causes, which I cover here). This happens when iron is lacking as plants can’t produce chlorophyll, which is what gives the plants the green color on their leaves and is also used to carry oxygen throughout the plant.
Without chlorophyll, plants lack oxygen and since photosynthesis is hindered, the plant won’t be able to get its energy from sunlight. Without knowing how to fix iron deficiency in plants, the lack of iron will eventually cause affected plants do die prematurely.
Recognizing the Early Stages of Iron Deficiency in Plants
As chlorophyll production is hindered when a plant has an insufficient supply of iron, you’ll notice the leaves turn yellow.
However, the earliest sign to look for is the yellowing on the veins of new leaves as those will lose their green first. This is called interveinal chlorosis and is the first indication of a nutritional imbalance.
Identifying the Cause of Iron Deficiency
While it is possible to try to fix iron deficiency in plants by using a fertilizer rich in iron, it’s not guaranteed to rectify a mineral imbalance. For plants to absorb iron from the soil, the iron needs to be in soluble form.
A range of factors in the soil condition, asides from the soil acidity can affect the solubility of many micronutrients.
Testing Soil for Nutrient Balance
Soil tests will generally test for soil acidity and won’t specifically tell you what minerals are available in soluble form. However, iron solubility is closely related to soil acidity.
The higher the pH, the more likely it is the iron molecules can latch onto other minerals, mainly calcium and phosphorous, therefore, making them insoluble, so while soils can be rich in iron, because they’re insoluble, plants can’t absorb them.
It’s for this reason soils need to have a balance of nutrients (macro and micronutrients), because a soil rich in iron is just as useless as having none if the iron can’t be absorbed by the plant.
Healthy soils with a balance of nutrients should be as close to pH 7 as possible. The higher the pH, the less soluble iron will be available.
In areas where the ground soil is calcareous, meaning it’s chalky and rich in calcium or limestone, will tend to lack other nutrients including phosphorous.
Different Ways to Increase Iron Consumption
Adjusting Soil pH
Alkaline soils (greater than pH 7) usually have a nutrient imbalance as they’ll lack zinc, iron and phosphorous. You can alter the pH levels by applying fertilizer, but that’s not always needed, nor favorable.
It can be more beneficial to add in organic matter such as peat moss and compost to your topsoil as those are rich in minerals. This isn’t directly altering the soil acidity, but rather making more nutrients available to the plant from the organic matter.
Treating Plants with Chelated Iron
Chelated irons are electrically charged molecules that hold the iron, preventing other minerals from affecting solubility. For that reason, iron chelates can be effective in alkaline soils. These are available as foliar sprays or in powder form to mix through your soil.
A foliar spray (view on Amazon) is applied to plant leaves only, giving the leaves a quick fix of iron, but it’s not going to last. It’ll need repeated spraying as it’s only a temporary fix to the plants leaves.
As a foliar spray won’t be reaching the roots of the plants, new leaves coming through are still going to be affected by interveinal chlorosis.
A longer-term solution is to treat the soil with iron chelates (view on Amazon). The type to use (and the cost) will be determined by your soil acidity.
The three types of chelated irons available include:
The most stable and most expensive type is Fe-EDDHA, which is stable in alkaline soils with a pH 9 and above. Fe-EDTA is stable in soils with a pH of 6.0, however as the pH rises by a half point (from 6.0 to 6.5), iron solubility decreases by as much as 50%.
If using this as a long-term solution to fix iron deficiency, temperature fluctuations should be considered because as temperatures increase, so too does the pH levels.
Fe-DTPA is stable in soils with pH under 7.0 with the main advantage being that they’re not as susceptible to iron replacement by calcium making this type a better chelated iron solution to use in calcareous soils.
How to Treat Iron Deficiency in Plants
The solution for iron deficiency in plants is to make more soluble iron available to the plants, which is best done by treating the soil. In particular, by altering the pH to make soil more acidic so that more nutrients are available in soluble form for the plant to absorb.
Chelated irons mixed into the soil are a good solution to enrich available iron in the soil, but it’s going to take time. Instead of waiting for your soil to change and the plant to get more iron in its diet, a foliar spray can be used to treat the leaves.
Foliar sprays shouldn’t be relied on as a long-term solution as they’re only going to treat the leaves and have no effect on the plant roots. That’s why it’s best to treat the soil rather than to treat the plant.
How you treat your soil depends on its pH levels. In sand, clay and loam soils, adding elemental sulfur is a fast (although not always permanent) way to reduce soil pH. In calcareous soils, it can be effective at increasing mineral availability by decreasing the pH by more than half a point, depending on the quantity used.
In addition to adding elemental sulfur, mix in some chelated iron that’s suited to your soil type, for example in soils rich in calcium, use Fe-DTPA, and for alkaline soils over pH 9, Fe-EDDHA would be better suited.
As treating the soil will take time for changes to happen, instead of waiting for the soil acidity to alter, you can use an iron foliar spray to treat the plant. This will encourage chlorophyll production, which in turn can help stimulate photosynthesis, helping to keep your plant alive until the soil becomes enriched in available iron in soluble form.
Growing up with a mom who filled her home (inside and out) with all sorts of plants, Lisa got her start in gardening at a young age. Living now on her own with a home and yard full of plants (including an indoor greenhouse), she shares all the gardening tips she’s gained over the years.