Pollination is the reproductive process where pollen is transferred from the male part of a flower to the female part, leading to fertilization. For pear trees, this step is necessary because it triggers the development of the ovary into the fruit and the formation of seeds. Successful fertilization determines whether a pear blossom will turn into a harvestable fruit, making the management of this process the most important factor in maximizing yield. Achieving maximum fruit set requires a strategic approach.
Understanding Pear Pollination Requirements
Most pear varieties, including many common European and Asian types, are considered self-unfruitful. They possess self-incompatibility, which prevents them from setting fruit with their own pollen. This requires cross-pollination, where pollen must come from a different, compatible variety. Even partially self-fertile varieties produce a significantly larger and higher-quality crop when cross-pollinated. The two varieties must be in bloom at the same time for the transfer to be effective.
To choose a suitable partner, pear cultivars are categorized into bloom groups, often labeled with letters or numbers, to indicate flowering timing. A tree can generally be cross-pollinated by any other variety in its own group or an immediately adjacent group, ensuring sufficient overlap in viable pollen availability. An important consideration is the ploidy level of the tree, which refers to its chromosome count.
Diploid pear varieties have two sets of chromosomes and produce high-quality pollen, making them excellent pollinators. Triploid varieties have three sets of chromosomes and produce mostly sterile pollen, rendering them ineffective as a pollen source. If you grow a triploid pear, you must plant two different diploid varieties nearby to pollinate both the triploid and each other, as the triploid cannot contribute to the cross-pollination cycle.
Selecting and Placing Cross-Pollinators
The most reliable, long-term strategy for ensuring cross-pollination is to plant a second, compatible pear variety with a synchronized bloom time. For successful pollen transfer by insects, the pollinator tree should be located within a maximum distance of 50 to 55 feet from the tree needing pollination. While European pears (Pyrus communis) and Asian pears (Pyrus pyrifolia) can cross-pollinate, their bloom windows do not always coincide. Therefore, it is safer to pair European with European and Asian with Asian varieties.
For gardeners with limited space, grafting a scion—a small cutting of a compatible pollinator variety—directly onto a branch of the main tree is highly effective. This creates a permanent, dual-variety tree where the pollen source is immediately available to foraging insects. The grafted branch must receive ample sunlight to encourage abundant flowering. Ensure the cambium layers of the scion and the host branch align for a successful union.
A temporary but practical solution is creating a “pollinator bouquet” during the bloom season. This involves cutting branches covered in open flowers from a compatible variety and placing the cut ends in a bucket of water. The bouquet should be hung within the canopy of the tree needing pollination, providing a concentrated source of viable pollen for visiting bees. This method supplements pollination for young trees that lack a pollinator graft or a second tree.
Techniques for Hand Pollination
Hand pollination provides manual intervention when natural insect activity is low due to poor weather or lack of suitable pollinators. The process requires precise timing, as the stigma (the female part of the flower) is only receptive for a short period. The ideal time to perform this task is on a dry, mild morning, preferably when temperatures are between 65 and 75 degrees Fahrenheit.
Begin by collecting pollen from the donor tree, which must be a compatible variety. Use a small, soft item like a fine-tipped paintbrush, cotton swab, or camel-hair brush to gently touch the anthers (the small, male structures) of a freshly opened flower. The goal is to collect a visible amount of the fine, powdery pollen onto the brush or swab.
Next, identify the receptive flowers on the receiving tree. A pear flower is ready when the stigma (the central female part) looks shiny and slightly gummy, allowing it to trap the pollen. Carefully transfer the collected pollen by gently dabbing the brush or swab directly onto the stigma. Repeating this action on numerous flowers across both varieties ensures the highest chance of successful fertilization.
Optimizing Conditions for Fruit Set
Beyond selecting the correct partner and performing manual transfer, optimizing the orchard environment significantly improves fruit set. Pear blossoms produce nectar that is less sugary than other fruit trees, making them less attractive to honeybees, which prefer higher-sugar sources. Encouraging alternative, highly efficient pollinators like the blue orchard mason bee is beneficial, as they are active in the cooler, early spring temperatures common during pear bloom.
You can attract these solitary bees by providing nesting materials, such as specialized nesting tubes or reeds, and a nearby source of moist mud, which they use to cap their nests. Avoid using broad-spectrum insecticides during the bloom period, as these chemicals can eliminate the insects required for pollen transfer. Minimizing competing blooms, such as dandelions, can help focus the attention of foraging bees on the pear flowers.
Environmental factors like cold and moisture can inhibit fruit set. Pear blossoms are susceptible to frost damage when temperatures drop below 28 degrees Fahrenheit, which can kill the reproductive parts of the flower.
Protecting Small Trees
For small trees, protection can be provided by covering the canopy with a cloth overnight.
Protecting Large Trees
For larger trees, commercial growers use overhead water sprinklers to coat the buds with ice, which protects the tissue underneath by releasing latent heat. Alternatively, they use wind machines to mix warmer air from higher elevations down into the orchard.