• elemental
Nitrogen Total (N) 0%
Phosphorus (P) 0%
Potassium (K) 0%
Iron (Fe) 17.80%

Osmocote Iron


  • General
  • Directions for use
  • Recommended application rates

This coating imparts controlled release characteristics to the Iron Sulphate, this being a great advantage for container nursery stock where Iron delivery in Iron-hungry wood waste potting mixes is critical.

Osmocote® Coated Iron Controlled Release Fertilizer provides a constant supply of essential iron for greener healthier plants for up to four months.

Growing plants must have a constant supply of iron because there is minimal movement of iron from old to new growth.

Osmocote Coated Iron has a benefit in potting soils where the plant will be growing for periods longer than 3 months. The use of powdered Iron Sulphate is adequate in shorter cultures, remembering to compensate for the overall pH drop that will result.


Product Advantages

  1. Unique Emax coating system.
  2. The coating system imparts controlled release characteristics to the Iron Sulphate.
  3. Provides a constant supply of essential iron for greener, healthier plants.
  4. Can be incorporated into potting mix or applied as topdress (not suitable for dibbling).
  5. Suitable for Australian and New Zealand native plants when use in conjunction with Osmocote Pro Low P products.


Directions for use

We recommend the use of Coated Iron in potting mixes for pots of half of one liter or above. This equates to pot sizes above a 10cm (3") tube. We do not recommend the use of Osmocote Coated Iron in pots or plugs smaller than this. In a small soil volume the distribution characteristics are not ideal and may cause injury to the young roots as has been seen in some isolated incidences.

A general rate of addition for Osmocote® Coated Iron is between 0.5 and 1.0 kg per cubic metre increasing to between 1.0 and 1.5 kg per cubic metre for Phosphorus sensitive plants, Iron-hungry crop or crops that have evolved in acidic soils such as Gardenia, Primula spp., Juniper and Rhododendron etc. When growing in potting soils with a peat content higher than 30% use the lower application rates.

  1. Pinebark and Sawdust Based Potting Mixes

Osmocote® Coated Iron is especially useful as an addition to potting mixes containing pinebark and/or sawdust as phenols in both products have a tendency to tie up iron making it unavailable to plants. Because Osmocote® Coated Iron releases slowly, over a period of time, there is a constant supply of iron available to plants, which can be used as it releases and before it is tied up by phenols.

  1. Australian Native Plants

Research has shown that phosphorus can cause toxicity problems with many Australian native plants, especially those in the Proteaceae family. The availability of phosphorus and iron is inter-related. A high level of one of these elements will make the other less available.

  1. Cooler Temperatures

At cooler temperatures Iron becomes less mobile in plants and therefore if a deficiency occurs it can be difficult and slow to rectify.

To overcome this problem, Osmocote® Coated Iron should be applied at potting time so that a deficiency does not occur.

  1. Plants Requiring Higher Level of Iron

Many plants require higher levels of iron, e.g., Azaleas, Camellias, Citrus, Ferns, Primulas and Gardenias. Application of Osmocote® Coated Iron at potting time can provide high levels of iron during the full growing season.

Caution: Do not use Osmocote® Coated Iron for tube stock or pot sizes less than 100mm or 1 liter. Trial first on small scale before rate, application or other changes in your cultural practices are implemented. As circumstances can differ and as the application of our products is beyond our control, ICL Specialty Fertilizers cannot be made responsible for any negative results.

Store in dry conditions. Partly used or damaged bags should be sealed.

Recommended application rates

Incorporate with potting mix, at potting time:

Low Medium High
300 g/m3 500 g/m3 800 g/m3



Pot Size

No. of Pots per m3

Low (g)

Medium (g)

High (g)

100mm (4”) 0.4L





125mm (5”) 1L





150mm (6”) 1.4L





175mm (7”) 2.5L





200mm (8”) 4.5L





250mm (10) 7L





Osmocote® Coated Iron is Iron Sulphate coated with ICL’s unique Emax® coating system.