Iron chlorosis

Symptoms of iron chlorosis

Iron chlorosis is characterised by abnormally yellow foliage, with the main veins remaining more or less green. Yellowing is observed on the young leaves at the tips of the shoots. The leaves undergo necrosis and fall off. This deficiency is not just an aesthetic problem, as iron is essential for chlorophyll synthesis; this lack leads to a slowdown in the growth of young plants and ultimately the death of the plant.

Foliage discoloration indicating chlorosis on a Banksia integrifolia.

You can observe this foliage discoloration on roses, ericaceous plants (Rhododendron, Camellia…) and many other ornamental plants, on citrus trees, and also in the vegetable garden: strawberry, artichoke, spinach, Swiss chard, and pumpkin can be affected.

Finally, it is possible to note a similar discoloration that may resemble iron chlorosis but is, in fact, a deficiency in magnesium or manganese. The discoloration does not appear in the same way:

• In the case of magnesium deficiency, yellowing starts on the older leaves and progresses from the edge of the leaf. However, a green band remains around the veins, and the discoloration is not as complete as in the case of iron deficiency.
• In the case of manganese deficiency, the leaves are slightly discoloured, appearing pale green, and the green veins, even the smallest ones, form a sort of checkerboard pattern.

Natural anti-chlorosis treatments

Commercial anti-chlorosis products, permitted in organic farming, contain iron in chelated form, meaning it is combined with a chemical or organic molecule, allowing the trace element to reach the roots without being blocked in the soil. Iron can be associated with magnesium, another essential component of chlorophyll. The products can be used for watering or spraying directly on the leaves depending on the formulation. However, be aware that these treatments are only effective in the short to medium term.

• Anti-chlorosis product based on chelated iron

The foliar spray of chelated iron is very spectacular, with plants greening up before your eyes! Spray the product as soon as symptoms appear, knowing that the optimal period is spring. However, even if the symptoms disappear, the problem persists. It is also important to keep the soil as alive as possible, particularly by regularly amending it with organic matter.

• Fermented nettle extract

The famous nettle manure has an anti-chlorosis effect. Rich in iron and numerous minerals, fermented nettle extract helps to correct chlorosis problems, for a time.

To use it, dilute it to 10%, that is, 1 litre of pure manure added to 9 litres of water in a 10-litre watering can. Water regularly to stimulate plant growth and combat ferric chlorosis.

→ Find out how to make nettle manure in our tutorial

• Foliar fertiliser

It is also possible to spray an anti-chlorosis foliar fertiliser every three weeks during the growing season.

Leaves of Hibiscus affected by ferric chlorosis.

Preventing the onset of chlorosis

You can prevent the appearance of iron chlorosis in the garden. To do this:

• Be aware that a heavy, overly wet soil, drought, and naked soil are aggravating factors. Therefore, to protect yourself from chlorosis: improve drainage, stimulate biological activity with amendments, and mulch.
• If your land is calcareous, avoid planting plants that are too sensitive to excess or that require acidic soil, such as rhododendrons, camellias, etc.
• Choose your roses grafted onto Rosa canina or laxa, rootstocks suitable for calcareous soil.
• Choose your fruit trees grafted onto a Saint-Julien plum tree or a Myrobalan.
• Mineral salt deficiencies are common for plants, especially citrus trees grown in pots. A potted plant only has what you give it to eat, so remember to feed it regularly.

Also, check out Olivier’s video tips on how to combat iron chlorosis.