Blue-eyed grass
Sisyrinchium angustifolium · Iridaceae
Not a grass but a tiny relative of the iris: tufts of narrow leaves with starry, violet-blue, yellow-eyed flowers in late spring.
- Size
- 14 in tall, 10 in wide
- Zones
- 4 to 9
- Light
- Full sun to part sun
- Flowers
- Mid May to late June
- Pets
- No toxicity recorded
- Job in a bed
- Edging
A bed built around blue-eyed grass
The planner designed this bed around blue-eyed grass when this page was made: a 12 × 6 ft (3.7 × 1.8 m) naturalistic planting in zone 6, full sun. It chose the other plants from the 966 that suit those conditions, and says below why blue-eyed grass stands where it does.
The plants
- 1 Blue-eyed grass × 14, blue
- 2 Winter heath × 10, pink
- 3 Blanket flower 'Arizona Sun' × 3, red
- 4 Garden phlox 'David' × 3, white
- 5 Switchgrass 'Cheyenne Sky' × 3, purple
- 6 Silver sage × 1, silver leaves
- 7 Ornamental onion 'Purple Sensation' × 4, purple
- 8 Darwin hybrid tulip × 12, yellow
Why this plant
- The only blue.
Why here
- In the middle. At 14 in it is the step between winter heath (10 in) in front and switchgrass 'Cheyenne Sky' (3 ft) behind: each is seen over the one before.
- A step in the back row. Next to garden phlox 'David' (3½ ft) and ornamental onion 'Purple Sensation' (2½ ft): no two neighbours there are the same height, so the back steps up and down like a skyline.
- 14 plants in 2 groups (8 and 6). Seen again further along, the same plant ties the bed together.
Why now
- In flower for six weeks. From mid May to late June.
- In company. With Darwin hybrid tulip in mid May: 2 kinds at once.
Planned as a naturalistic planting: low grasses and groundcovers, the matrix, make up 53% of the planted ground. The flowering is at its height from late July, with 3 kinds out together. Winter heath is planted in four places along the bed, which gives it rhythm.
The planner's own design check: 10 Excellent, 7 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 blue-eyed grass goes in a border
At 14 in it belongs at the front of a bed. In the planner's ten height classes it is short (12 to 18 in).
Its job: edging. A low, neat plant used in short runs of three or five along the front to finish the edge (or, in a formal bed, in one even row).
The flowers open only in sun. Plant it in groups at the very front, where the small flowers can be seen. It is short-lived but self-seeds, and likes moist soil.
- Edging moist paths
- Native meadows
- Fine, grassy texture at the front
What to plant with blue-eyed grass
Plants recorded as good partners for it, and what each pairing does:
- Golden Alexanders: blue against yellow, opposite each other on the colour wheel, in flower together for five weeks; tall enough (2½ ft) to stand behind it; happy in the same moist soil.
- Wild geranium: in flower together for three weeks, from mid May; happy in the same moist soil.
- Dwarf crested iris: low enough (6 in) to stand in front of it.
Questions about blue-eyed grass
Does blue-eyed grass need sun or shade?
Blue-eyed grass grows in full sun (6 or more hours of direct sun a day) and part sun (4 to 6 hours of sun, including some afternoon sun).
It wants soil that stays evenly moist, of average fertility, and a good soak in dry spells.
What zones does blue-eyed grass 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 blue-eyed grass flower in my zone?
In zone 5 it flowers mid May to late June. As a spring flower it moves about a week for every zone: earlier where it is warmer, later where it is colder.
| Zone 4 | Late May to late June |
|---|---|
| Zone 5 | Mid May to late June |
| Zone 6 | Early May to late June |
| Zone 7 | Early May to mid June |
| Zone 8 | Late April to mid June |
| Zone 9 | Mid April to early June |
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 blue-eyed grass be planted?
8 in (20 cm) apart, from the middle of one plant to the middle of the next. That is a little closer than its full width of 10 in (25 cm), so a group knits into one patch.
It grows 14 in (35 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.
How many blue-eyed grass plants do I need?
At 8 in apart, set out in staggered rows:
- 27 to fill 10 square feet (about 1 m²)
- 16 for a single row 10 ft (3 m) long
- 86 to fill a 4 × 8 ft bed on its own
In a mixed border, plant it as runs of three or five along the front (or one even row, in a formal bed).
In the bed above, the planner used 14 in two groups.
Is blue-eyed grass 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.
Do deer eat blue-eyed grass?
They may. NC State does not list it as resistant to deer or rabbits. Where they visit, protect it, or plant it among ones they avoid.
What flowers after blue-eyed grass?
Blue-eyed grass is over by late June. These start as it finishes and carry the same spot on, so it never goes flat:
- Black-eyed Susan: from mid July to mid September, 24 in tall.
- Butterfly weed: from late June to early August, 24 in tall.
- Yarrow: from mid June to late August, 24 in tall.
What does blue-eyed grass look like in winter?
Blue-eyed grass holds some of its leaves into winter, more in a mild year or a sheltered spot, and they look tired by March. Cut the old ones off as new growth starts.
Is blue-eyed grass good for bees and butterflies?
Blue-eyed grass is visited by bees.
It is native to the United States and Canada.
In these guides
- Pet-safe plants for a sunny border
- Native perennials for pollinators
- Garden plants native to Canada
- Plants for bees
- Plants with blue flowers
Zone guides: Zone 4 · Zone 5 · Zone 6 · Zone 7 · Zone 8 · Zone 9
Every fact on record
- Type
- Perennial
- Size
- 14 in (35 cm) tall, 10 in (25 cm) wide
- Plant
- 8 in (20 cm) apart
- Height class
- Short (12 to 18 in)
- Place in the bed
- Front
- Flowers
- Mid May to late June; blue
- Leaves
- Fine texture, semi-evergreen; green
- Shape
- Upright, clumping
- Hardy in
- USDA zones 4 to 9
- Light
- Full sun, part sun
- Soil
- Average, evenly moist
- Water
- Moderate
- Feeding
- Light, in spring
- Family
- Iridaceae
- Comes from
- North America
- Attracts
- Bees
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.