Cross-Pollination of Blackberry Bushes

Blackberries (Rubus spp.) make an easy-to-grow plant for the home garden in U.S. Department of Agriculture plant hardiness zones 5 through 10. You can choose to grow trailing vines that require support, or varieties that have an upright growth and do not need support. Most blackberry plants have thorns, but thornless cultivars are available. While you'll find both self-fruitful and self-unfruitful, to ensure a good yield of berries, it is recommended that you plant several different varieties of blackberries to encourage cross pollination.

Growing Self-fruitful Blackberries

Self-fruitful blackberries can set fruit using their own pollen; however, the flowers do require pollinators, such as native bees, honeybees or the wind, to transfer pollen from the anther of the male flower to the stigma of the female flower on the same plant. While the plants will produce fruit without planting a second variety, all blackberry plants produce a better fruit yield when two or more compatible plants are placed close together.

Growing Self-unfruitful Blackberries

Self-unfruitful blackberries require another blackberry plant of a compatible cultivar to act as a pollinizer. To ensure proper cross-pollination of self-unfruitful blackberries, the pollinizer must have a bloom time that overlaps the main plant's bloom period and produce a large amount of pollen. Honeybees are important pollinators. They work in rows, so to increase pollination you can intermix the main plants and the pollinizers. If possible, try to plant pollinizers that also set edible fruit.

The Importance of Cross-Pollination

Proper pollination of blackberry plants helps ensure a better yield and prevents the growth of misshapen fruit. Adequate pollination also increases the rate of fruit maturity. Pollinators transfer pollen to fertilize flowers and encourage seed formation. Blackberry seeds stimulate the growth of ovarian tissue, which is the fruit flesh. Properly fertilized flowers produce more seed and bigger fruit. Factors other than pollinators and pollinizers can interfere with cross-pollination, such as rain, excessive heat and wind.

Spacing for Blackberry Plants

Proper spacing of both erect and trailing blackberries is important to ensure adequate cross-pollination and plant health.The exact spacing is dependent on cultivar selection and the limitation of machinery used on the property. When planting blackberry plants, space erect blackberry varieties 3 feet apart, while planting trailing varieties 5 to 8 feet apart, leaving 8 feet between rows. For good fruit production, blackberries need adequate moisture, so ensure plants get about an inch per week.

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