Sea holly 'Big Blue'
Eryngium x zabelii 'Big Blue' ·
Spiny flower heads as wide as a hand, in an intense, iridescent blue that runs down the stems, on a sturdy, branching plant.
- Size
- 2½ ft tall, 24 in wide
- Zones
- 4 to 9
- Light
- Full sun
- Flowers
- Late June to late August
- Pets
- Not checked
- Job in a bed
- Accent
A bed built around sea holly 'Big Blue'
The planner designed this bed around sea holly 'Big Blue' when this page was made: a 12 × 6 ft (3.7 × 1.8 m) English border 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 sea holly 'Big Blue' stands where it does.
The plants
- 1 Sea holly 'Big Blue' × 2, blue
- 2 Cheddar pinks 'Firewitch' × 8, pink
- 3 Heath aster 'Snow Flurry' × 4, white
- 4 Brown-eyed Susan × 5, yellow
- 5 Silver sage × 1, silver leaves
- 6 Wild quinine × 5, white
- 7 Schubert's allium × 3, pink
- 8 Daffodil × 10, orange
Why this plant
- The only blue.
Why here
- In the middle. At 2½ ft it is the step between silver sage (12 in) in front and wild quinine (3½ ft) behind: each is seen over the one before.
- 2 plants in 2 places. An accent is a punctuation mark: the repeat along the bed gives it rhythm.
Why now
- In flower for 9 weeks. From late June to late August.
- Part of the bed's peak. With brown-eyed Susan and wild quinine in late July: 3 kinds at once. No week has more.
Planned as an English border: 5 of the 5 groups (100%) are drifts, longer along the bed than they are deep. Brown-eyed Susan and wild quinine anchor the back corners of the bed: the tallest plants on the plan stand there. The scheme leans cool (blue and pink) and uses yellow and orange for warmth, with white to calm things between them.
The planner's own design check: 13 Excellent, 4 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 sea holly 'Big Blue' goes in a border
At 2½ ft it belongs in the middle of a bed. In the planner's ten height classes it is medium (24 in to 2½ ft).
Its job: accent. An upright plant used singly, like a punctuation mark, and repeated at intervals to give the bed rhythm.
The showiest sea holly for general garden use: large flowers, strong colour and a longer life than most. The colour is best in full sun and poor soil.
- Strong blue for dry borders
- Cutting and drying
- Bees
What to plant with sea holly 'Big Blue'
Plants recorded as good partners for it, and what each pairing does:
- Yarrow 'Terracotta': blue against orange, opposite each other on the colour wheel, in flower together for nine weeks; happy in the same dry soil.
- Mexican feather grass: in flower together for five weeks, from late June; happy in the same dry soil.
- Sedum 'Matrona': in flower together for two weeks, from mid August; bold leaves against its medium ones; happy in the same dry soil.
Questions about sea holly 'Big Blue'
Does sea holly 'Big Blue' need sun or shade?
Sea holly 'Big Blue' grows in full sun (6 or more hours of direct sun a day).
It wants dry, sharply drained soil, on the lean side, with no feeding, and little watering once settled.
What zones does sea holly 'Big Blue' 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 sea holly 'Big Blue' flower in my zone?
In zone 5 it flowers late June to late August. As a summer flower it moves about half a week for every zone: earlier where it is warmer.
| Zone 4 | Early July to late August |
|---|---|
| Zone 5 | Late June to late August |
| Zone 6 | Late June to late August |
| Zone 7 | Late June to mid August |
| Zone 8 | Late June to mid August |
| Zone 9 | Mid June to early August |
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 sea holly 'Big Blue' be planted?
18 in (45 cm) apart, from the middle of one plant to the middle of the next. That is a little closer than its full width of 24 in (60 cm), so a group knits into one patch.
It grows 2½ ft (75 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.
How many sea holly 'Big Blue' plants do I need?
At 18 in apart, set out in staggered rows:
- 5 to fill 10 square feet (about 1 m²)
- 7 for a single row 10 ft (3 m) long
- 17 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 two in two groups.
What flowers after sea holly 'Big Blue'?
Sea holly 'Big Blue' is over by late August. These start as it finishes and carry the same spot on, so it never goes flat:
- Sedum 'Matrona': from mid August to early October, 24 in tall (a recorded partner).
- Garden chrysanthemum: from mid September to late October, 24 in tall.
- Bottle gentian: from late August to early October, 20 in tall, to stand in front of it and cover its fading stems.
What does sea holly 'Big Blue' look like in winter?
Sea holly 'Big Blue' 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 Eryngium
- Alpine sea holly Eryngium alpinum
- Mediterranean sea holly Eryngium bourgatii
- Miss Willmott's ghost Eryngium giganteum
- Rattlesnake master Eryngium yuccifolium
- Sea holly Eryngium planum
- Sea holly 'Blue Hobbit' Eryngium planum 'Blue Hobbit'
In these guides
Zone guides: Zone 4 · Zone 5 · Zone 6 · Zone 7 · Zone 8 · Zone 9
Every fact on record
- Type
- Perennial
- Size
- 2½ ft (75 cm) tall, 24 in (60 cm) wide
- Plant
- 18 in (45 cm) apart
- Height class
- Medium (24 in to 2½ ft)
- Place in the bed
- Middle
- Flowers
- Late June to late August; globes; blue
- Leaves
- Medium texture, herbaceous; green, blue-green
- Shape
- Upright, clumping
- Hardy in
- USDA zones 4 to 9
- Light
- Full sun
- Soil
- Lean, dry and sharply drained
- Water
- Low
- Feeding
- None needed
Not yet checked against an outside reference: its figures rest on general horticultural knowledge. 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.