Frost-Damaged Plants: Which Fertiliser and Which Practices Help Recovery

What happens to a frost-damaged plant?

What to apply to a frost-damaged plant is among the questions growers ask most, especially in spring and autumn when frost risk is high. Frost forms ice crystals in plant tissue, tears cell membranes and halts water and nutrient transport. The damaged plant shows yellowing, a wilted appearance, leaf scorch and fruit drop.

The severity of frost damage depends directly on how long the temperature stayed below 0°C and on the plant's nutritional status beforehand. A well-fed plant with full reserves of calcium and potassium comes through a frost event far more lightly.

What to do before frost

Acting after damage costs far more than acting before it. When frost is forecast, take these steps:

• Potassium application: potassium concentrates the cell sap and lowers the freezing point. Apply a foliar potassium fertiliser 48–72 hours before expected frost.
• Calcium application: strengthens the cell wall and increases resistance to ice crystal formation.
• Casablanca application: containing trace elements and natural biostimulants, it prepares the plant against abiotic stress.
• Night irrigation: light irrigation on a frost night can exploit the latent heat effect · but the technique requires experience.

The frost has hit · what now?

The first 72 hours after damage are critical. While the plant tries to recover from damaged tissue, it must not be put under additional stress.

1. An immediate foliar application

24–48 hours after the frost damage, when conditions allow (a still, mild day), a liquid foliar fertiliser should be applied. This application:

• Quickly compensates for nutrient loss
• Triggers the formation of new leaves and shoots
• Helps balance the effect of stress hormones (ethylene, ABA)

2. A zinc + iron combination

Zinc and iron are the most critical micronutrients for regenerating damaged tissue. Zinc acts in enzyme activation, iron in chlorophyll synthesis. In a frost-hit plant, chlorophyll production stops; iron support speeds that process back up.

3. Do not rush to cut damaged tissue

Pruning immediately after frost damage puts the plant under a second stress. Wait at least 10–14 days, until the boundary between living and dead tissue is clear, before pruning.

Which plants are most sensitive to frost?

Tomato, pepper, aubergine, banana, citrus saplings and young olive trees are the most frost-sensitive. In these species, a few hours of frost can wipe out a whole season's work.

The role of Casablanca in frost stress

The natural components in the Casablanca formulation support the mechanisms that raise abiotic stress tolerance:

• Osmotic regulation: the concentration of dissolved solutes inside the cell rises and the freezing point falls
• Antioxidant activity: the plant's defence against free radicals produced by cold stress is strengthened
• Faster re-greening: the formation of new shoots and leaves after frost is accelerated

Application programme

Before frost (48–72 hours): Casablanca 150 ml per 100 L of water as a foliar spray
After frost (24–48 hours): Casablanca 200 ml per 100 L of water, plus the same rate through the drip system
Recovery period (7–10 days): repeat the foliar application weekly

Frequently asked questions

When should fertiliser be applied to a frost-damaged plant?

The first application should be made 24–48 hours after the frost, when conditions allow. Never during or immediately after the frost · wait until the plant begins to come out of shock.

How is frost damage recognised?

Yellowing leaves, brown scorch marks, wilting and signs of water cut-off are the indicators. Fruit and flowers are affected first.

What should be done for a frost-hit fruit tree?

Apply zinc + iron foliarly within the first 48 hours. Wait at least 10–14 days before pruning. Restrict nitrogen and bring calcium and potassium to the fore.

Is frost insurance enough on its own?

Insurance compensates the financial loss but does not save the season. With a correct fertiliser programme frost damage can be minimised and the plant recovers faster. The two should be considered together.