The possible causes of iron deficiency in Petunia and Primula

What's the cause?

Iron is present in the growing media, but it cannot be taken up by the plants. This can be due to high growing media pH in the area around the roots of the plant, this is described as the nutrient being “unavailable”.

The cause can be:

• The starting pH of the growing media is higher than 6.5.
• The form of chelated iron in your growing media is better suited to a different pH range.
• Irrigation with hard, untreated water, particularly when using overhead irrigation, causes growing media pH to rise.

What if the pH is not high?

The plants may not be able to take up iron if there are very high levels of other nutrients, this is described as “incompatibility”.   

When you think you may have iron deficiency it is important to check for high levels of phosphorus (P), manganese (Mn) and zinc (Zn) in the growing media and feed.

Another factor that may cause an iron deficiency is if there  are poor water levels in the growing media, either too low or too high -  both of these will cause iron to be unavailable.