Agastache ‘Blackadder’ or Giant Hyssop Blackadder, is a herbaceous perennial from the Mint Family or Lamiaceae family of plants. It is a hardy plant. This cultivar is sterile.
It has deep purple-violet flowers on spikes that grow to about 3′ tall in summer and fall. The flowers are ideal for borders. They attract butterflies. Agastache ‘Blackadder’ leaves are aromatic with a hint of anise and the flower creates interest in the landscape all the way into winter.
The flowers are tubular and two-lipped. The spikes of flowers are about 8in or 20cm. The leaves are blue-green and they form a clump where spikes of flowers then grow from. Agastache Blackadder is drought-tolerant and heat-tolerant once it is established. They are also deer and rabbit resistant.
Plant them in full sun in rich and fertile and well-drained soil. It is important that the soil is well-drained as Agastache Blackadder does not like wet soil during winter.
Propagate from semi-ripe cuttings in summer or by division. Agastache Blackadder is generally pest-free and disease-free. But watch out for powdery mildew. Agastache Blackadder dies back at end of autumn and regrows in spring.