Thornless blackberries, including popular cultivars like ‘Navaho’, ‘Arapaho’, and ‘Triple Crown’, offer gardeners easy harvesting without the threat of thorns. These varieties still produce long, vigorous canes that become heavy when fruit-laden, raising the question of support. The need for a trellis depends entirely on the specific cultivar’s natural growth habit. While some erect varieties can manage without assistance, most thornless types benefit significantly from a support system to maximize health and yield.
Understanding Blackberry Growth Habits
The requirement for a trellis is directly linked to whether a blackberry plant is classified as erect, semi-erect, or trailing. Erect varieties, such as ‘Navaho’ or ‘Arapaho’, feature stiff canes that stand upright, often requiring minimal support. These canes are naturally rigid and maintain an upward posture as they mature.
Semi-erect cultivars, like ‘Triple Crown’ and ‘Chester Thornless’, have vigorous canes that tend to arch and sprawl when weighed down by fruit. These flexible canes can reach 10 to 15 feet in a single season, making a trellis highly recommended for organization. Trailing varieties have long, limber canes that must be trellised because they completely lack structural rigidity. Without support, the canes of semi-erect and trailing types will quickly collapse and lie on the ground.
Advantages of Structural Support
Implementing a trellis system provides multiple horticultural benefits that justify the effort, even for varieties that could technically stand alone. Keeping the canes off the soil dramatically improves sanitation by preventing fruit contact with the ground, which reduces rot and minimizes pest access. This elevation is particularly beneficial for disease management, as it promotes better air circulation, helping leaves and fruit dry faster after rain or dew.
Training the canes to wires ensures uniform sunlight penetration, which enhances fruit quality and increases the overall yield. The organized structure also simplifies harvesting, making the berries easy to find and pick. The support prevents heavy, fruit-laden canes from breaking or becoming tangled, maintaining the plant’s productive architecture throughout the season.
Selecting and Installing Trellis Systems
The choice of trellis system should align with the blackberry’s growth habit. The simple I-trellis, or vertical trellis, uses a single line of posts with parallel wires strung between them, making it well-suited for erect or semi-erect types. For highly vigorous semi-erect varieties, a V-trellis is often preferred; it uses angled posts to create a V-shape, allowing floricanes to be tied to the outer wires while new primocanes grow vertically in the center.
For installation, durable posts (such as treated wood or metal) should be set two to three feet deep for stability and spaced 15 to 30 feet apart along the row. A common wire configuration uses two to three galvanized wires, often 12.5-gauge for the top wire and 14-gauge for lower wires. Wires are typically positioned at heights like three and five feet from the ground, providing points for cane support. While specialized systems like the Rotating Cross-Arm (RCA) trellis exist, the I-trellis or a simple two-wire system is highly effective for home gardens.
Pruning and Training Supported Canes
Effective management of a trellised blackberry patch requires distinct pruning and training actions throughout the growing season. Blackberries operate on a biennial cane cycle, where new vegetative shoots (primocanes) grow in the first year. These then become floricanes, which produce fruit and subsequently die, in the second year. Training begins by loosely tying or weaving the developing primocanes onto the trellis wires as they grow.
A practice called “tipping” is performed on primocanes when they reach five to six feet tall or about 12 inches above the top wire. Tipping involves pinching off the growing tip, which stops vertical growth and encourages the development of lateral branches where next year’s fruit will form. During the dormant season, spent floricanes (canes that finished fruiting) must be cut completely to the ground. Simultaneously, the mature lateral branches on the remaining floricanes are shortened to 12 to 18 inches to prevent overcropping and maintain air circulation.