Companion planting involves strategically placing different plant species near each other for mutual benefits, such as improved soil health or pest control. For blackberries, the focus shifts to avoiding specific neighbors that can actively harm the health or productivity of the cane fruit. Incompatible plants can introduce devastating diseases, share pests, or aggressively compete for limited resources. Understanding these detrimental relationships is important for maintaining a robust and high-yielding blackberry patch.
High-Risk Disease Hosts
The most significant threat to a blackberry planting comes from plants that harbor soil-borne pathogens, even if the host plant appears healthy. The fungal disease Verticillium wilt is particularly destructive to cane fruits. Certain garden vegetables are notorious carriers of the causative fungi, Verticillium dahliae and V. albo-atrum. These fungi can persist in the soil for years as dormant resting structures called microsclerotia, making the area permanently unsuitable for blackberries.
Plants belonging to the Solanaceae family, commonly known as nightshades, should be strictly avoided near blackberries. This family includes common garden staples such as tomatoes, potatoes, peppers, and eggplants. Solanaceous crops are highly susceptible to Verticillium wilt, allowing the fungus to multiply in the soil. Planting blackberries in soil that recently grew these vegetables significantly increases the risk of the fungus infecting the blackberry roots, leading to wilt and eventual death.
Strawberries are also high-risk companions because they are susceptible to the same soil-borne Verticillium wilt fungus. Strawberries are known to host viruses, such as Strawberry necrotic shock virus, which can transmit to Rubus species. Introducing strawberries near blackberries creates a shared reservoir for multiple damaging pathogens. Avoid planting blackberries in any area where these high-risk hosts have grown within the last three to five years.
Related Species and Cross-Contamination
Planting blackberries near other members of the Rubus genus, such as red raspberries, black raspberries, and hybrid cane fruits like loganberries, is highly discouraged. While these plants share similar growing needs, their close genetic relationship means they are vulnerable to the same diseases and pests. This shared susceptibility creates a pathway for rapid cross-contamination and the spread of systemic issues.
The primary concern is the easy transmission of viruses that are often symptomless in one species but devastating in another. For instance, Raspberry bushy dwarf virus (RBDV) can spread between Rubus plants through pollen, potentially leading to crumbly, misshapen blackberry fruit. Shared pests like cane borers also move easily between closely spaced plantings, causing widespread damage. Maintaining a substantial physical distance, ideally 50 feet or more, between different Rubus varieties helps to mitigate this risk.
Aggressive Competitors and Physical Inhibitors
Certain plants should be excluded from the blackberry patch because they deplete resources or physically overwhelm the blackberry’s shallow root system. Blackberries are relatively light feeders, but they require consistent access to water and nutrients to produce a good harvest. Planting heavy feeders nearby, such as asparagus or artichokes, results in direct competition for soil nutrients, which can stunt growth and reduce fruit yield.
Physical dominance is another concern, particularly with plants that grow large or spread vigorously. Artichokes and Canna lilies can grow tall and wide, casting heavy shade over the blackberry canes and interfering with air circulation. Blackberries require full sun for optimal fruiting, and excess shade will severely reduce productivity. Canna lilies spread aggressively through underground rhizomes, which can directly compete with and inhibit the establishment of blackberry roots.
Even some otherwise beneficial herbs, like oregano or certain types of mint, can become detrimental if not contained. These plants spread aggressively and can quickly choke out the blackberry’s root zone, turning into a dense mat that suffocates the soil and monopolizes water. Additionally, certain trees, most notably walnuts (Juglans species), release a chemical called juglone from their roots, which is known to be toxic to many plants, including some brambles, inhibiting their growth.