Big bluestem 'Blackhawks'
Andropogon gerardii 'Blackhawks' ·
A big bluestem whose dark green leaves turn deep purple and then almost black by late summer, on a narrower, more upright plant than the species.
- Size
- 5 ft tall, 24 in wide
- Zones
- 4 to 9
- Light
- Full sun
- Flowers
- Mid August to late September
- Pets
- No toxicity recorded
- Job in a bed
- Accent
A bed built around big bluestem 'Blackhawks'
The planner designed this bed around big bluestem 'Blackhawks' when this page was made: a 12 × 6 ft (3.7 × 1.8 m) contemporary bed in zone 6, full sun. It chose the other plants from the 966 that suit those conditions, and says below why big bluestem 'Blackhawks' stands where it does.
The plants
- 1 Big bluestem 'Blackhawks' × 4, purple
- 2 Bloody cranesbill × 3, pink
- 3 Creeping phlox 'Emerald Blue' × 5, blue
- 4 Swamp milkweed 'Ice Ballet' × 3, white
- 5 Globe arborvitae 'Danica' × 1, green leaves
- 6 Joe-Pye weed 'Baby Joe' × 3, pink
- 7 Grecian windflower × 10, blue
Why this plant
- The only airy sprays. The others are open bowls, flat plates, dense clusters and others. Shape reads at a distance, where colours blur.
- The only purple.
- Part of the bed's structure. Shrubs and grasses keep their shape when the perennials die down. So does globe arborvitae 'Danica'.
Why here
- Anchors a back corner. At 5 ft it is the tallest plant 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 joe-Pye weed 'Baby Joe' (2½ ft) and swamp milkweed 'Ice Ballet' (3½ ft): no two neighbours there are the same height, so the back steps up and down like a skyline.
- 4 plants in 2 places. An accent is a punctuation mark: the repeat along the bed gives it rhythm.
Why now
- In flower for 7 weeks. From mid August to late September.
- Closes the season. For its last two weeks nothing else on the plan is in flower.
- Stands through winter. Left uncut, it holds its shape until March, when the perennials have gone.
Planned as a contemporary bed: 27 of the 27 plants that stand in groups (100%) are set out in a pattern with their neighbours: a straight row, a triangle, or five like the five on a dice. Low plants run along 99% of the front edge: bloody cranesbill and creeping phlox 'Emerald Blue'. The most in flower at one time is 3 kinds, in late July.
The planner's own design check: 12 Excellent, 4 Good, 1 Satisfactory. 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 big bluestem 'Blackhawks' goes in a border
At 5 ft it belongs at the back of a bed. In the planner's ten height classes it is tall (4 to 5 ft).
Its job: accent. An upright plant used singly, like a punctuation mark, and repeated at intervals to give the bed rhythm.
The darkest tall grass there is. Set it behind golden flowers, such as goldenrod, or pale seed heads, so the colour shows.
- Dark vertical foliage
- Contrast with gold and silver
- Prairie-style borders
What to plant with big bluestem 'Blackhawks'
Plants recorded as good partners for it, and what each pairing does:
- Goldenrod 'Fireworks': purple against yellow, opposite each other on the colour wheel, in flower together for five weeks.
- Purple coneflower: in flower together for four weeks, from mid August; low enough (3 ft) to stand in front of it.
- Sedum 'Autumn Joy': in flower together for seven weeks, from mid August; bold leaves against its fine ones; low enough (24 in) to stand in front of it.
Questions about big bluestem 'Blackhawks'
Does big bluestem 'Blackhawks' need sun or shade?
Big bluestem 'Blackhawks' grows in full sun (6 or more hours of direct sun a day).
It wants ordinary well-drained soil, of average fertility, and little watering once settled.
What zones does big bluestem 'Blackhawks' grow in?
USDA zones 4 to 9. It is hardy to zone 4, which means it survives winter nights down to about −20 °F (−29 °C).
Gardening in Canada? Use the USDA zone for your town: Canada's own zone map uses different numbers.
When does big bluestem 'Blackhawks' flower in my zone?
In zone 5 it flowers mid August to late September. As a summer flower it moves about half a week for every zone: earlier where it is warmer.
| Zone 4 | Late August to late September |
|---|---|
| Zone 5 | Mid August to late September |
| Zone 6 | Mid August to late September |
| Zone 7 | Early August to late September |
| Zone 8 | Early August to late September |
| Zone 9 | Early August to late September |
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 big bluestem 'Blackhawks' be planted?
24 in (60 cm) apart, from the middle of one plant to the middle of the next. That is about its full width, so each plant keeps its own outline.
It grows 5 ft (150 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.
How many big bluestem 'Blackhawks' plants do I need?
At 24 in apart, set out in staggered rows:
- 3 to fill 10 square feet (about 1 m²)
- 6 for a single row 10 ft (3 m) long
- 10 to fill a 4 × 8 ft bed on its own
In a mixed border, plant it as one at a time, repeated along the bed at intervals; a slender one reads better as a clump of three.
In the bed above, the planner used four in two groups.
Is big bluestem 'Blackhawks' 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 big bluestem 'Blackhawks'?
Big bluestem 'Blackhawks' is not native to North America. These North American natives come closest to doing its job:
- Switchgrass 'Northwind': the same job in a bed, the same size and the same flowering time; tan, not purple.
- Indian grass: the same job in a bed and the same flowering time; 12 in taller, tan, not purple.
- Little bluestem 'Standing Ovation': the same job in a bed and the same flowering time; 20 in shorter, 6 in narrower.
Matched the way the planner's Swap button matches plants: the same job in a bed, then size, then flowering time.
What flowers after big bluestem 'Blackhawks'?
Big bluestem 'Blackhawks' is over by late September. These start as it finishes and carry the same spot on, so it never goes flat:
- Tatarian aster 'Jindai': from early October to early November, 4 ft tall.
- Willowleaf sunflower 'First Light': from mid September to mid October, 4 ft tall.
- Aromatic aster 'Raydon's Favorite': from mid September to early November, 3 ft tall, to stand in front of it and cover its fading stems.
What does big bluestem 'Blackhawks' look like in winter?
Big bluestem 'Blackhawks' turns the colour of straw and, left uncut, stands through the winter. Cut it down in late winter, before the new shoots come up.
More Andropogon
- Big bluestem Andropogon gerardii
In these guides
- Pet-safe plants for a sunny border
- Tall perennials and grasses for the back of a border
- Plants that flower in fall
- Plants with purple and burgundy leaves
Zone guides: Zone 4 · Zone 5 · Zone 6 · Zone 7 · Zone 8 · Zone 9
Every fact on record
- Type
- Grass
- Size
- 5 ft (150 cm) tall, 24 in (60 cm) wide
- Plant
- 24 in (60 cm) apart
- Height class
- Tall (4 to 5 ft)
- Place in the bed
- Back
- Flowers
- Mid August to late September; airy sprays; purple
- Leaves
- Fine texture, herbaceous; dark green, purple
- Shape
- Upright, clumping
- Hardy in
- USDA zones 4 to 9
- Light
- Full sun
- Soil
- Average, well-drained
- Water
- Low
- Feeding
- None needed
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.