Various cultivars of Navel and Valencia oranges, mandarins and mandarin hybrids are prone to fruit splitting, a pre-harvest physiological rind disorder. Gardeners often wonder if this phenomenon is caused by a nutrient deficiency. Actually, there’s another cause, but plant nutrition can play a part in the splitting of citrus peel.
How does citrus peel split?
Citrus peel splitting often occurs in periods of drought or dry spells followed by heavy rains, and is caused by environmental factors – extreme fluctuations in temperature, humidity and soil moisture. Inconsistent watering, allowing a tree to get very dry, then giving it water, can cause citrus fruit to split, and is the most common cause in home gardens.
The process by which citrus peel splits is as follows. Citrus trees are fairly shallow rooted trees, and in hot, dry weather, they’re likely to experience dry soils and moisture shortages. If the trees aren’t watered for a while and allowed to get quite dry, and are then irrigated or experience heavy rainfall, they’ll take up plenty of water, and the fruit does too, swelling up relatively quickly.
The peel of citrus fruit is fairly flexible, but In hot, dry weather, the peel becomes tougher and less elastic, so it doesn’t stretch as easily. If the fruit begins to swells from the inside very quickly, the peel will split at the weakest point, resulting in fruit splitting.
Nutrient deficiency and peel splitting
When a citrus tree has deficiencies in potassium or calcium, the rind tends to be thinner or weaker, making it more prone to splitting. Providing a citrus tree with adequate potassium and calcium when fertilizing will therefore minimize the splitting of fruit.
Crop load and fruit splitting
The severity of citrus fruit splitting is very much dependent on the final crop load, how much fruit the tree is carrying. The higher the crop load, the higher the percentage of split fruit. With low crop loads, very few fruit will split.
The more fruit a tree carries, the less water and nutrients it can apportion to each fruit, resulting in fruit that is smaller in size with a thinner skin. In citrus trees, the levels of potassium, which support the development of a healthy thick peel, will drop during heavy crop loads.
One way to reduce crop loads in a tree is by pruning, which has the added benefit of producing less fruit of a higher quality and larger size, rather than lots of little fruit.
Preventing fruit splitting
Reducing the physiological stress on a citrus tree will minimise the chances of fruit splitting, and this can be done by:
- Consistent watering, not allowing a citrus tree to get too dry.
- Correct feeding, ensuring that the tree is provided with the nutrients it requires from a balanced fertiliser which supplies all the macronutrients as well as the micronutrient required.
- Reducing crop load can through appropriate pruning.