Troubles with Raspberry Cross-Pollination

Function

• Raspberry pollen is loose on the top of stamens but is not apt to be blown about by wind. The top surface of pistils is sticky, allowing any pollen that lands there to stay in place. Bees use nectar to produce honey, and they move pollen onto pistils in the process of harvesting nectar. Without adequate nectar, bees are unable to flourish and increase their numbers. Without pollination, raspberries and other brambles do not produce sufficient seeds to maintain the population of their species.

Cross-Pollination

• When a pistil is fertilized by pollen, a seed containing an embryo is formed. This embryo becomes a new plant if conditions are correct. During the embryo's development, hormones that are produced direct the production of fruit. Raspberry fruit is made up of individual drupelets, each of which contains one seed. When fertilization occurs with pollen from a different raspberry plant, which is cross-pollination, then the drupelets are larger and contain more juice than when fertilization occurs within one plant. Because commercially grown raspberries are not grown from seeds, the genetics of their seeds doesn’t matter. The fruit is considered much better, and that is why cross-pollination is desirable.

Bees

• About $15 billion worth of crops are dependent upon bees for pollination in the United States each year, according to a 2008 on the Natural Resources Defense Council's website. About one-third of all U.S. bee hives have vanished, that article states. The phenomenon is called Colony Collapse Disorder and is believed to be the result of a variety of factors. One of the factors is the increased use of insecticides commercially and by home gardeners. Using insecticides only when necessary, using only those that have fewer effects on bees than other insecticides and applying only the amount needed can help. Apply an insecticide in late afternoon or evening, when bees are less active than during other times of the day. Most importantly, do not apply an insecticide during flowering time, when bee activity on raspberry plants is critical.

Tips for Success

• Healthy raspberry plants from a reputable nursery are intended to produce for many years. Plant raspberries 2 feet apart in rows 8 to 10 feet apart, depending on the available space. They need a location where the soil is well-drained and where they will be warmed by sunlight in morning, when bees are most active. Keep the area between the plant rows clean, and use mulch on the soil to avoid weeds along the rows, ensuring bees will be attracted to raspberry blossoms rather than weed blossoms. Planting different kinds of raspberry plants will give variety to your harvest and help to ensure cross-pollination for an increased yield.