Iron fertiliser for plants is sometimes necessary if the soil does not contain enough iron. However, if the deficiency is due to the plant’s inability to absorb the mineral properly, other measures can also help. Find out more in this article.
When do plants need iron fertiliser?
Iron is important for plants so that they can produce sufficient chlorophyll. This is the pigment that gives them their green colour and also plays a central role in photosynthesis – in other words, in the plant’s energy metabolism.
- If a plant does not have a sufficient supply of iron, it will show this through pale to yellow leaf colour or patches. This condition is also known as ‘chlorosis’.
- Typically, it is primarily the young shoots that are broadly discoloured, whilst the leaf veins remain green. Yellow leaves also occur in the case of magnesium deficiency. However, this usually affects the older, fully grown leaves.
- As a result of iron deficiency, the plant no longer grows well, its flowering is reduced and it is more susceptible to pests.
- Iron deficiency is particularly common in the following plants: citrus trees, rhododendrons, roses, blackberries, hydrangeas, azaleas, tomatoes and petunias.
Identifying the causes
Before reaching for an iron fertiliser, you should try to identify the cause of the iron deficiency. This will determine the appropriate further care required for the soil and the plants.
- It may well be that there is actually enough iron in the soil. However, the iron is sometimes bound so tightly in the soil that the plants are unable to absorb it.
- The availability of iron does depend on the soil’s pH level. Acidic soils with a pH between 5 and 6 release iron most effectively.
- However, if the soil becomes increasingly alkaline – for example, due to watering with hard water – and reaches a pH of 7 or higher, the iron is usually bound very tightly. Certain plants then develop calcium chlorosis.
- In this case, it helps to stop watering with hard water. It is best to use rainwater. Furthermore, you should not use nitrate fertilisers, as these also lower the pH level.
- You can improve the availability of iron by working in compost, bog soil and spruce needles, and by loosening the soil to prevent waterlogging.
- However, if a pH test reveals that the pH is below 6.5, there may indeed be an iron deficiency in the growing medium, and an extra application of the mineral may remedy the situation.
How to use the right iron fertiliser
There are various types of iron fertiliser. In principle, many complete fertilisers already contain sufficient iron. However, you can also use specialised iron fertilisers, which in turn vary greatly in terms of their active ingredients.
- Ferrous sulphate: This is produced from iron and sulphuric acid. It is a toxic substance that you should only use whilst taking appropriate precautions and strictly following the instructions for use. When mixed with water, iron sulphate is corrosive.
- You must therefore always wear safety goggles and gloves when using iron(II) sulphate. Wear long clothing and sturdy footwear.
- If you are using ferrous sulphate on your lawn to control moss, ensure that children and pets are kept away from the area for the next few days.
- Ferrous sulphate is usually available in granule form. You can spread it by hand or over a large area using a spreader. Follow the manufacturer’s dosage instructions. Watering is usually carried out after application.
- Water-soluble iron chelates (EDTA): This is far less fussy to use. It is usually sold in liquid form and can be added to the watering can. The positive effects of top-dressing are often somewhat delayed.
- Foliar feeding is also possible with EDTA. Spray the diluted iron fertiliser directly onto the plant using a spray bottle. This allows the plant to absorb and utilise the iron directly.
- As a general rule for widespread iron fertilisation: ensure that you do not track iron fertiliser around with your gardening shoes. This is particularly important with ferrous sulphate. The iron would leave unsightly stains on surfaces such as concrete paving slabs and similar materials.
