Blackberries

By Linda Lewis Griffith, UC Master Gardener

 
Planting

• Plant blackberries in the dormant season, mainly in December and January.  
• Dig a hole large enough to accommodate the roots.  Prune off any damaged roots. Spread healthy roots within hole.  Plant so that base of stalk is 1” higher than level of soil. Press firmly to remove air pockets.  Water thoroughly to settle soil and apply mulch.
• Space plants 3-4 feet apart in the row allowing 8-10 feet between rows.
• Cut canes on new plants to 6 inches.

Sunlight and Soil

• Blackberries require full sun.  
• Although they do well in a variety of soils, they perform best in sandy loam, or loam soils with a pH of 5.5-7.0.
• Soils should be well-drained to a depth of at least 2 feet.  
• If your soil is poorly drained, plant on a small mound or berm.  

Water and Fertilizer

• Blackberries require frequent irrigation during the growing season, ensuring they are always moist but not saturated.
• Provide 1-2 inches of water per week from mid-May through October, irrigating two times per week.  
• Overhead irrigation is not recommended as it promotes fruit rot and other diseases
• Fertilize with annual application of nitrogen fertilizer prior to growing season in January.  Apply 5-6 pounds of 20-20-20 fertilizer per 100 feet of row.  If you use manure or compost, apply in late fall or early winter to allow leaching of excess salts by rain.

Trellising

• Blackberries require a trellis system to support the fruiting canes.  A two-wire system is usually adequate, with the top wire approximately 3½ feet above the ground.  Strong galvanized wire should be used for strength and durability.  Install the trellis system before planting.

Pruning

• No pruning is needed during the first year after planting.
• During the first growing season, use the trellis to support new canes growing from the plant crowns.  Tie or wrap the canes around the wire. These canes will bloom and produce the first crop the following spring.  
• In the spring, new canes (called primocanes) will grow along the ground.  Keep these canes on the ground to prevent injury.   

After harvest, cut off the old canes (called floricanes) down to the ground.  Train 3-5 of the new year’s canes onto the trellis.  Trim canes to 5-6 feet.

Each year, remove spent floricanes and replace them with the healthiest primocanes from the current season.

Pests and Diseases

• The spotted wing drosophila is a tiny fruit fly (1/8” inch) that infests ripening berries by laying eggs in the fruit.  Larvae appear as tiny white worms. Minimize infestations by removing any fallen or infected fruit and by harvesting fruit as they ripen. The use of plastic mulch under the plants has been shown to reduce infestation of fruit. 
• Redberry mites are invisible to naked eye and cause the fruit to remain red, hard and sour. All or only patches of the berry may be affected. Sulfur applied after budbreak and at bloom or horticultural oil applied at green berry stage will help control.
• White drupelet is an abiotic disorder due to weather conditions and not insect pests. It appears as a tan to white discoloration of individual berry seeds or bumps (drupelets) and is associated with high heat, wind and low humidity.
• Leaf and cane rust- Yellow-orange fungal spores appear on both canes and the undersides of leaves but no leaf cupping or distortion. Affects trailing blackberries such as olallieberries. Treat with copper fungicide. Associated with wet springs.
• Orange rust- Early growth weak and spindly, leaves cupped and distorted with orange fungal spores on rim and undersides of leaves, spores not on canes. Does not affect trailing type blackberries. No treatment but removal of entire plant is recommended. Associated with cool temperatures and high humidity.

References

Blackberries. University of California the California Garden Web. Blackberries - The California Garden Web 

“Caneberries-Leaf and Cane Rust.” UCIPM. Cane and Leaf Rust / Caneberries / Agriculture: Pest Management Guidelines / UC Statewide IPM Program (UC IPM)

McIntosh, Hanna, Michael Bartlett Smith et al. Modifications of plant microclimate by plastic mulches reduces Drosophila suzukii infestation. Journal of Pest Science. 12 Jan 2024. https://link.springer.com/article/10.1007/s10340-023-01715-4

“Orange Rust Emerging Again in Blackberry.” Strawberries and Caneberries. UCANR. 2011. Orange rust emerging again in blackberry - Strawberries and Caneberries - ANR Blogs

UCIPM Spotted Wing Drosophila Management Guide. Spotted Wing Drosophila Management Guidelines--UC IPM