Botanical Name: Agastache ‘Black Adder’

Common Name: Hummingbird Mint, Anise Hyssop Hybrid

Hardiness Zone: Perennial in Most Climates (USDA Zones 6–10)

Size: 30–36" Tall × 18–24" Spread

Growth Habit: Upright, Clump-Forming Habit

Sunlight: Thrives in Full Sun

Soil: Prefers Well-Drained Soil; Tolerates Poor or Rocky Soils

Water Needs: Low to Moderate Once Established; Drought Tolerant

Bloom Season: Early Summer through Fall

Fertilizer: Light Feeding in Spring; Avoid Excess Nitrogen

Features: Deep Blue-Purple Flower Spikes, Dark Calyxes, Aromatic Foliage, Deer Resistant, Exceptional Pollinator Plant

Uses: Ideal for Pollinator Gardens, Perennial Borders, Cottage Gardens, and Naturalistic Plantings

Patent: ❌ Not Patented

Propagation: ✔ Propagation Allowed

See our complete Agastache Growth & Care Guide for full care details.

More About Agastache ‘Black Adder’

Agastache ‘Black Adder’ is one of those plants that still stops me in my tracks, even after decades of growing Agastache. The contrast is what hooks you first—the rich violet-blue flower spikes rising out of nearly black calyxes give it a depth you don’t see in many perennials. From across the garden, it reads bold and architectural, but up close it has a lot of nuance. I’ve found it especially effective when it’s planted among softer colors, where that dark undertone really has room to shine.

Black Adder came out of early hybrid work between Agastache foeniculum and Agastache rugosa, and you can see the influence of both parents if you’ve grown them long enough. It carries that familiar anise scent and cold tolerance I associate with classic hyssop, but with fuller flower spikes and a longer bloom window. The upright stems hold their flowers well, creating strong vertical lines that keep the garden looking lively from early Summer straight into Fall. It’s a plant that adds structure without feeling stiff.

Why We Like It (Our Trials)

In our time testing different Agastache, ‘Black Adder’ has earned its reputation as a true pollinator powerhouse. On warm days, it’s rarely quiet—bees working the flowers nonstop, butterflies passing through, and hummingbirds returning again and again. If someone tells me they want a plant that actually brings wildlife into the garden, this is one I don’t hesitate to recommend. Once established, it’s surprisingly tough. As long as the soil drains well, it handles heat and dry stretches without much complaint. 

I also appreciate that it hasn’t been bred into a tight little mound like some newer Agastache varieties. That slightly looser habit gives it movement, which makes it feel at home in larger borders, meadow-style plantings, and pollinator gardens where everything doesn’t need to be perfectly clipped. Deer have consistently ignored it for us, and that aromatic foliage seems to help with that. ‘Black Adder’ may not be the newest introduction anymore, but it’s one of those plants that proves its worth year after year. It brings height, contrast, and life into the garden—and after more than 50 years of gardening, those are qualities I value deeply.

Black Adder vs. Other Agastache Varieties

Black Adder is considered the benchmark for tall, dramatic Agastache. Compared to its little brother, Little Adder, Black Adder grows taller and airier, making it better suited for mid- to back-of-border placements where height and movement are desirable. Compared to warm-toned varieties like Kudos™ Mandarin or Kudos™ Coral, Black Adder brings a cooler, darker contrast to the garden, adding depth and structure where those brighter hues tend to feel lighter and more playful.

When contrasted with modern, densely flowered varieties such as Blue Boa, Black Adder appears more open and meadow-like, offering a lighter, less congested silhouette. Blue Fortune shares a similar airy character but with a softer blue tone, but Black Adder delivers deeper color and stronger contrast. For gardeners who prioritize height, hummingbird attraction, and a more traditional prairie aesthetic, Black Adder is the Agastache for you.