Botanical Name: Agastache x 'Black Adder'
Common Name: Giant Hyssop  
Plant photo of: Agastache x 'Black Adder'
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Water Saving Tip:

Apply as little fertilizer as possible.

If you use fertilizer make sure it stays on the landscape, and carefully water it in so there is NO runoff.

  • Anatomy

  • Culture

  • Design

Plant Type

Perennial, Herb


Height Range



Flower Color

Red, Violet


Flower Season

Summer, Fall


Leaf Color



Bark Color



Fruit Color



Fruit Season



Full, Half



Low, Medium


Growth Rate



Soil Type

Sandy, Clay, Loam


Soil Condition

Average, Rich, Poor, Well-drained, Dry


Soil pH

Neutral, Basic


Adverse Factors


Design Styles

English Cottage, Mediterranean, Ranch, Spanish


Accenting Features

Fragrance, Showy Flowers


Seasonal Interest



Location Uses

Perennial Border, Raised Planter


Special Uses

Container, Small Spaces


Attracts Wildlife

Hummingbirds, Butterflies

Information by: Stephanie Duer
  • Description

  • Notes

'Black Adder' is an upright, clump-forming giant hyssop that grows to 2 to 3 feet tall and about 2 feet wide. It has a long summer-to-frost season of bloom, with tubular, smoky red-violet flowers that emerge from nearly black buds that bloom in showy, bottle-brush, spikes. Aromatic (anise/licorice scented), lance-shaped to ovate leaves are blue green. Flowers are attractive to bees, hummingbirds and butterflies. Not as drought tolerant as its desert kin, but still a worthwhile addition to the herb garden.
Grow in average, dry to medium moisture, well-drained soils in full sun to part shade, though best in full sun. Good soil drainage is essential. Plants will perform poorly and may not survive winter in unamended clay soils or over-watered soils. Plants tolerate heat and some dry soils once established. Deadhead spent flower blooms to promote additional bloom. Cut back the dead stems in late winter to early spring.