Citrus Fruit and Blossom Drop

CITRUS FRUIT AND BLOSSOM DROP

Tales from a Desert Gardener
by Steve Fazio, Horticulturist

“My fruit tree is dropping all of its blossoms – my fruit tree didn’t bloom this year – fruit is falling from the tree.” These remarks are expressed by many gardeners in connection with citrus and deciduous fruit trees. What caused these problems? Some are related to cultural management practices, temperature; others are normal plant responses.

Citrus trees will cause the greatest concern for most gardeners – they will shed many blossoms and later in the season, fruit as large as walnuts will fall to the ground. All varieties of citrus produce more blossoms than the tree can possibly set – approximately 98% will fall even under the best cultural management practices. If 2% of the blossoms set fruit, this would be considered a heavy commercial crop. This is a natural behavior of the trees, but failure for 2% to set fruit is related to many factors. Late spring frost that occurs during bloom period causes a weakening or death of the abscission layer. This layer of cells connects the flower to the tree – sub-freezing conditions injure the cells, and blossom drop will result.

Trees that were not fertilized prior to the bloom period often drop excess number of blossoms, especially if soil fertility was extremely low. The tree is reacting in a natural manner – it is ridding itself of a burden. Improper irrigation is also responsible for blossom drop. Fruit trees in the blooming stage require very special attention in connection with soil moisture – they should never be allowed to stress for water – this will weaken the connecting layer. Trees should not be over watered at this stage – irrigation should be maintained on the same level used during the growing season – irrigate when soil examination reveals a need for moisture, but do it on a more careful basis during bloom.

Some varieties of citrus may fail to produce blossoms – gardeners will often state, “Last year my tree had a profusion of blossoms, and I had a heavy crop of fruit – no blossoms are evident this year.” This condition is common with some varieties of mandarins – the Kinnow mandarin is one of the main culprits. This condition is referred to as “alternate bearing” – a heavy bloom one year and none the next. This occurs on other citrus varieties, but not as pronounced as the mandarins. Commercial growers will often state, “My orange and grapefruit crop is on the light year cycle.” Others may state, “My crop is on the heavy cycle.” Trees that produce a heavy crop one year will usually produce a lighter crop the following year – this is alternate bearing on the light side.

The heartbreak of growing citrus is called “June drop.” This occurs when fruit the size of a pea or as large as a walnut fall from the tree. It is caused by high temperatures and low humidity – it will be evident starting in May and extending through the month of June. Trees should be checked at frequent intervals during the stress period for soil moisture – fruit drop is aggravated by moisture deficiency.