Hyssop 'Black Adder'
Agastache 'Black Adder' · Lamiaceae
Smoky violet-blue bottlebrushes rise from dark purple buds for three months or more, over leaves that smell of liquorice.
- Size
- 3 ft tall, 18 in wide
- Zones
- 6 to 9
- Light
- Full sun
- Flowers
- Late June to early October
- Pets
- No toxicity recorded
- Job in a bed
- Drift
A bed built around hyssop 'Black Adder'
The planner designed this bed around hyssop 'Black Adder' when this page was made: a 12 × 6 ft (3.7 × 1.8 m) cottage garden in zone 6, full sun. It chose the other plants from the 715 that suit those conditions and its dry soil, and says below why hyssop 'Black Adder' stands where it does.
The plants
- 1 Hyssop 'Black Adder' × 5, purple
- 2 Creeping phlox 'Candy Stripe' × 5, pink
- 3 Sea thrift × 4, white
- 4 New England aster 'Alma Pötschke' × 4, pink
- 5 Silver sage × 1, silver leaves
- 6 Butterfly weed × 3, orange
- 7 Star of Persia × 5, purple
- 8 Ornamental onion 'Purple Sensation' × 5, purple
Why this plant
- The only spires. The others are open bowls, globes, daisies and others. Shape reads at a distance, where colours blur.
Why here
- Anchors a back corner. At 3 ft it is one of the taller plants here, and the tallest close the ends of the bed, where they stand in front of nothing.
- A step in the back row. Next to New England aster 'Alma Pötschke' (3½ ft): no two neighbours there are the same height, so the back steps up and down like a skyline.
- 5 plants in one group. Massed, one kind reads as a single shape. Scattered, it would look spotty.
Why now
- In flower for 15 weeks. From late June to early October.
- Fills a gap. For two of those weeks nothing else on the plan is in flower.
Planned as a cottage garden: 22 of the 22 plants (100%), bulbs aside, stand alone or in groups of no more than five, small enough for the kinds to mingle. Low plants run along 93% of the front edge: silver sage, creeping phlox 'Candy Stripe' and sea thrift. Purple is the colour seen most, on 3 of the 7 kinds grown for their flowers.
The planner's own design check: 14 Excellent, 3 Good. It flags one thing to watch: Nothing on this plan is highly poisonous or an aggressive spreader.
Open this bed in the planner Change its size, the sun or the style, move plants about, or swap one for another.
Where hyssop 'Black Adder' goes in a border
At 3 ft it belongs in the middle of a bed. In the planner's ten height classes it is medium tall (2½ to 3 ft).
Its job: drift. Planted in a small group of three or five, and repeated further along in the other number.
Darker and longer in flower than 'Blue Fortune', and sterile, so it does not seed about. Bees work it from first flower to frost. It needs sharp drainage to come through winter.
- Long-flowering spires for pollinators
- Gravel gardens
- Late-summer colour with grasses
What to plant with hyssop 'Black Adder'
Plants recorded as good partners for it, and what each pairing does:
- Purple coneflower: in flower together for 11 weeks, from late June.
- Prairie dropseed: in flower together for six weeks, from mid August; a low mound at the foot of its spires; happy in the same dry soil.
- Black-eyed Susan: purple against yellow, opposite each other on the colour wheel, in flower together for 11 weeks.
Questions about hyssop 'Black Adder'
Does hyssop 'Black Adder' need sun or shade?
Hyssop 'Black Adder' grows in full sun (6 or more hours of direct sun a day).
It wants dry, sharply drained soil, of average fertility, and little watering once settled.
What zones does hyssop 'Black Adder' grow in?
USDA zones 6 to 9. It is hardy to zone 6, which means it survives winter nights down to about 0 °F (−18 °C).
Gardening in Canada? Use the USDA zone for your town: Canada's own zone map uses different numbers.
When does hyssop 'Black Adder' flower in my zone?
In zone 5 it flowers late June to early October. As a summer flower it moves about half a week for every zone: earlier where it is warmer.
| Zone 6 | Late June to early October |
|---|---|
| Zone 7 | Late June to early October |
| Zone 8 | Late June to early October |
| Zone 9 | Mid June to early October |
Worked out from Hopkins' bioclimatic law: spring arrives about four days later for each degree of latitude north, and one zone is roughly two degrees. A warm spring or a cold one moves any garden two weeks either way.
How far apart should hyssop 'Black Adder' be planted?
16 in (40 cm) apart, from the middle of one plant to the middle of the next. That is a little closer than its full width of 18 in (45 cm), so a group knits into one patch.
It grows 3 ft (90 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.
How many hyssop 'Black Adder' plants do I need?
At 16 in apart, set out in staggered rows:
- 7 to fill 10 square feet (about 1 m²)
- 8 for a single row 10 ft (3 m) long
- 21 to fill a 4 × 8 ft bed on its own
In a mixed border, plant it as a group of three or five, with a second group further along in the other number.
In the bed above, the planner used five in one group.
Is hyssop 'Black Adder' poisonous to dogs and cats?
No toxicity is recorded for dogs, cats, horses or people, according to NC State Extension.
"Not toxic" is not "edible": a pet that eats a lot of any plant can be sick.
Is there a native plant like hyssop 'Black Adder'?
Hyssop 'Black Adder' is not native to North America. These North American natives come closest to doing its job:
- Purple coneflower: the same job in a bed, the same size and the same colour; flowers late June to early September, wants average soil.
- Texas hummingbird mint: the same job in a bed, the same size and the same flowering time; pink, not purple, fine leaves, not medium.
- Gloriosa daisy 'Indian Summer': the same job in a bed, the same size and the same flowering time; yellow, not purple, wants average soil.
Matched the way the planner's Swap button matches plants: the same job in a bed, then size, then flowering time.
What flowers after hyssop 'Black Adder'?
Hyssop 'Black Adder' is over by early October. These start as it finishes and carry the same spot on, so it never goes flat:
- Chrysanthemum 'Sheffield Pink': from late September to early November, 2½ ft tall.
- Saffron crocus: from early October to early November, 5 in tall, to stand in front of it and cover its fading stems.
- Japanese onion 'Ozawa': from early October to early November, 10 in tall, to stand in front of it and cover its fading stems.
What does hyssop 'Black Adder' look like in winter?
Hyssop 'Black Adder' dies down to the ground and there is nothing to see until spring. The old stems can be cut in autumn, or left until spring as shelter for overwintering insects.
More Agastache
- Anise hyssop Agastache foeniculum
- Hyssop 'Blue Boa' Agastache 'Blue Boa'
- Hyssop 'Blue Fortune' Agastache 'Blue Fortune'
- Sunset hyssop Agastache rupestris
- Texas hummingbird mint Agastache cana
In these guides
- Pet-safe plants for a sunny border
- Plants with spires: vertical accents
- Long-flowering plants: 12 weeks or more
- Plants with blue flowers
Every fact on record
- Type
- Perennial
- Size
- 3 ft (90 cm) tall, 18 in (45 cm) wide
- Plant
- 16 in (40 cm) apart
- Height class
- Medium tall (2½ to 3 ft)
- Place in the bed
- Middle
- Flowers
- Late June to early October; upright spires; purple, blue
- Leaves
- Medium texture, herbaceous; green
- Shape
- Upright, clumping
- Hardy in
- USDA zones 6 to 9
- Light
- Full sun
- Soil
- Average, dry and sharply drained
- Water
- Low
- Feeding
- None needed
- Family
- Lamiaceae
Checked against NC State Extension. Flowering times are for zone 5: later in colder zones, earlier in warmer ones. Toxicity and spread information is a general gardening guide, not veterinary or medical advice, and invasive status varies by region. If a person or pet eats a plant, contact poison control or a vet. Check your local invasive species list before planting anything with a spread warning.