Hollies (Ilex spp.) are dioecious, meaning that they produce male and female flowers on different plants. The most common reason for a lack of berries is that the tree is a male or that a male tree is not available nearby to pollinate a female one.

The male pollinator does not need to be right next to the female plant. Hollies are pollinated mainly by bees. Even 200 feet is within the range that bees can carry pollen. A large male holly tree can pollinate numerous female trees.

Hollies are most efficiently pollinated by plants of the same species or variety. Thus, the ‘Jersey Knight’ cultivar of the American holly is able to pollinate many other female American hollies. For English holly (Ilex aquifolium) cultivars, which are very popular hollies, specific cross-fertilizing pairs have been developed, e.g. ‘Silver Milkboy’ and ‘Silver Milkmaid’, or ‘China Boy’ and ‘China Girl’.

There are a few self-pollinating hollies (strictly “parthenocarpic” or sterile plants).  For these you need to grow only the female plants. Examples are Ilex x ‘Nellie Stevens’ and Ilex cornuta ‘Burfordii’.

There are a number of other reasons why hollies may not produce fruit:

• The tree is too young. Hollies grown from seeds require 3-5 years or even longer to bloom. Trees grown from cuttings need only 1-2 years before they bloom.
• The bee population may be low that particular year or bad weather may have interfered with their pollination.
• If the tree is growing in poor conditions, a cycle may develop of alternate good and poor years for berry production.
• Too much or too little nitrogen-rich fertilizer can be a problem.
• Very dry weather may cause a tree to drop its flowers or berries.
• Over-pruning or early pruning can also be a reason. If flowers are cut off in the spring, obviously no berries can be produced. Summer or early fall pruning may remove stems that would bloom next spring.
• A late frost may kill the flowers in spring.
• All hollies do not bloom at the same time. Thus, if the male plant is not blooming at the same time as the females, fertilization cannot occur.
• Although reputable nurseries properly label plants, mistakes can be made--you may have a male plant!

It is important to note that deciduous hollies are also dioecious. For example, for the commonly grown Sparkleberry deciduous holly (I. serrata x vertilicillata ‘Sparkleberry’), a male companion (‘Apollo’) from the same cross is available.

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- Courtesy of NYBG Plant Information Service