The physical dimensions a blackberry plant reaches are not fixed but vary significantly depending on the specific variety and the grower’s management style. Understanding the plant’s natural growth habit is the first step in determining space requirements. A compact variety intended for a container will have vastly different needs than a vigorous, sprawling commercial cultivar.
Understanding Growth Habits: The Key to Size Variation
Blackberry plants (Rubus genus) are classified into three categories based on the natural structure and rigidity of their canes. This growth habit directly dictates the plant’s potential height and spread. The three types are erect, semi-erect, and trailing, each requiring different levels of support.
Erect varieties, such as ‘Prime-Ark Traveler’, produce stiff, self-supporting canes. These canes grow upright from the crown, forming a dense, shrub-like hedge that requires minimal trellising. They are the most manageable for small garden spaces due to their vertical nature.
Semi-erect cultivars have canes that start upright but eventually arch over, requiring a trellis system for support and to keep fruit off the ground. While they often yield higher fruit production than erect varieties, their sprawling nature takes up more lateral space. This habit is a middle ground between erect and trailing types.
Trailing blackberries, like the ‘Marionberry’, produce long, flexible canes that will sprawl along the ground if they are not trained onto a supportive trellis. These canes can be extremely vigorous, sometimes growing over 15 feet long in a single season. The trailing habit prioritizes horizontal coverage, making it necessary to manage their extensive spread over a wide area.
Typical Mature Dimensions and Space Requirements
The mature size of a blackberry plant depends on its cane length and the spacing required for healthy air circulation and light penetration. Erect varieties, whose canes can reach 5 to 8 feet, are typically maintained at 3 to 3.5 feet through annual trimming. Growers space these plants 2.5 to 4 feet apart in the row, allowing them to merge into a productive hedgerow.
Spacing Requirements
Semi-erect and trailing types demand significantly more room to accommodate their extensive cane length. Semi-erect plants should be spaced 4 to 5 feet apart within the row. Trailing plants often need 5 to 8 feet of space between plants to fan out their long canes. For all varieties, rows should be spaced 6 to 12 feet apart. The wider spacing is reserved for the most vigorous semi-erect and trailing types to allow for harvesting and maintenance access.
For gardeners with limited space, dwarf varieties offer a highly compact option. Cultivars like ‘Baby Cakes’ typically reach a maximum height and spread of just 3 to 4 feet. These compact plants often do not require any trellising and are suitable for growing in large containers on a patio, providing fresh fruit without the commitment of a full-sized planting.
Managing Plant Size Through Annual Pruning
The maximum natural size of a blackberry is rarely reached in a managed environment because the gardener actively controls its dimensions through pruning. Blackberries have a biennial fruiting cycle where canes, known as primocanes, grow vegetatively in the first year, and then those same canes, now called floricanes, produce fruit and die in the second year. This cycle is the basis for size management.
A primary technique for controlling height and encouraging a manageable shape is tipping, or heading back, the new primocanes. When a primocane reaches a height of about 3 to 5 feet, the top few inches are removed, which stops vertical growth. This action redirects the plant’s energy into developing lateral, or side, branches, which keeps the plant shorter and bushier.
Controlling the plant’s width is achieved by pruning these lateral branches back to 12 to 18 inches during the dormant season. This not only manages the overall spread but also concentrates the fruit production closer to the main cane. Furthermore, the complete removal of old floricanes immediately after they finish fruiting is necessary to thin the plant’s density, preventing overcrowding and ensuring that new primocanes have adequate light and space to grow.