What are the possible causes of leaf edge scorch in Primula?

What is the cause of leaf scorch?

There is not just one cause of leaf tissue death, this can be due to nutrition, water availability or the growing environment.

Like tip burn in lettuce, or blossom end rot in tomato, leaf edge scorch in primula can be caused by poor calcium levels.

Why is calcium important?

Calcium is an important part of the walls of a plant cell, the building blocks of the plant. If there is not enough calcium in the cell walls, they breakdown and that part of the tissue dies.

In young leaves as the they grow, the area of the problem may distort the leaf and cause more damage.

Where does the plant get calcium from?

• Growing media that has been adjusted to increase the pH will have calcium rich compounds added, such as calcium carbonate (CaCO₃).
• Some types of feed will have calcium as part of the mix, such as those containing calcium nitrate (Ca(NO₃)₂).
• Irrigation water from hard water areas will naturally contain calcium carbonate (CaCO₃) if it is not acidified.
• In low pH growing media and irrigation water that is soft or treated water, calcium may be deficient. 

What affects calcium levels in the leaf?

Calcium moves from the growing media to the leaf in the water that flows through the plant, this process of water movement is also known as transpiration. Anything that negatively affects a good supply of water moving through the plant will negatively affect the supply of calcium to where the plant needs it. This can be:

• Growing media that is too dry, especially in the evening.
• High humidity around the growing point of the plant that stops water loss from the leaf.

There can be enough calcium present in the water supply, feed and growing media but environmental conditions can prevent it reaching the part of the plant where it is needed.