Alpine sea holly
Eryngium alpinum ·
Large, cone-shaped flower heads, each sitting in a ruff of soft, feathery, metallic-blue bracts like a lace collar. The upper stems are blue as well.
- Size
- 2½ ft tall, 18 in wide
- Zones
- 4 to 8
- Light
- Full sun
- Flowers
- Late June to early August
- Pets
- Not checked
- Job in a bed
- Accent
A bed built around alpine sea holly
The planner designed this bed around alpine sea holly 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 966 that suit those conditions, and says below why alpine sea holly stands where it does.
The plants
- 1 Alpine sea holly × 2, blue
- 2 Moor grass 'Greenlee' × 6, tan
- 3 Cheddar pinks 'Tiny Rubies' × 16, pink
- 4 New England aster 'Alma Pötschke' × 4, pink
- 5 Silver sage × 1, silver leaves
- 6 Purple coneflower × 3, purple
- 7 Golden garlic × 12, yellow
- 8 Spring starflower × 8, blue
Why this plant
- The only globes. The others are spires, open bowls, daisies and others. Shape reads at a distance, where colours blur.
Why here
- In the middle. At 2½ ft it is the step between moor grass 'Greenlee' (12 in) in front and New England aster 'Alma Pötschke' (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 7 weeks. From late June to early August.
- Part of the bed's peak. With moor grass 'Greenlee', Cheddar pinks 'Tiny Rubies' and purple coneflower in late June: 4 kinds at once. No week has more.
Planned as an English border: 4 of the 5 groups (80%) are drifts, longer along the bed than they are deep. The scheme leans cool (blue, pink and purple) and uses yellow for warmth, with tan to calm things between them. The bed is balanced: the left half carries 51% of the visual weight and the right half 49%.
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 alpine sea holly 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 largest and softest ruff of any sea holly: it looks sharp and is not. Unlike its relatives it likes ordinary, fairly rich soil. A superb cut and dried flower.
- Steel blue for the middle of a border
- Cutting and drying
- Contrast with soft, mounded plants
What to plant with alpine sea holly
Plants recorded as good partners for it, and what each pairing does:
- Yarrow 'Moonshine': blue against yellow, opposite each other on the colour wheel, in flower together for seven weeks.
- Blue oat grass: in flower together for two weeks, from late June.
- Catmint 'Walker's Low': in flower together for seven weeks, from late June.
Questions about alpine sea holly
Does alpine sea holly need sun or shade?
Alpine sea holly 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 alpine sea holly grow in?
USDA zones 4 to 8. It is hardy to zone 4, which means it survives winter nights down to about −20 °F (−29 °C).
Above zone 8 it struggles: the zones measure winter cold, but a plant's top zone usually means the summers are too hot or the winters too mild for it to rest.
Gardening in Canada? Use the USDA zone for your town: Canada's own zone map uses different numbers.
When does alpine sea holly flower in my zone?
In zone 5 it flowers late June to early August. As a summer flower it moves about half a week for every zone: earlier where it is warmer.
| Zone 4 | Early July to mid August |
|---|---|
| Zone 5 | Late June to early August |
| Zone 6 | Late June to early August |
| Zone 7 | Late June to early August |
| Zone 8 | Late 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 alpine sea holly 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 2½ ft (75 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.
How many alpine sea holly 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 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 alpine sea holly?
Alpine sea holly is over by early August. These start as it finishes and carry the same spot on, so it never goes flat:
- Lilyturf: from early August to mid September, 16 in tall, to stand in front of it and cover its fading stems.
- Sedum 'Autumn Joy': from mid August to mid October, 24 in tall.
- Little bluestem 'Standing Ovation': from early August to mid September, 3½ ft tall.
What does alpine sea holly look like in winter?
Alpine sea holly 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
- Mediterranean sea holly Eryngium bourgatii
- Miss Willmott's ghost Eryngium giganteum
- Rattlesnake master Eryngium yuccifolium
- Sea holly Eryngium planum
- Sea holly 'Big Blue' Eryngium x zabelii 'Big Blue'
- Sea holly 'Blue Hobbit' Eryngium planum 'Blue Hobbit'
In these guides
Every fact on record
- Type
- Perennial
- Size
- 2½ ft (75 cm) tall, 18 in (45 cm) wide
- Plant
- 16 in (40 cm) apart
- Height class
- Medium (24 in to 2½ ft)
- Place in the bed
- Middle
- Flowers
- Late June to early August; globes; blue
- Leaves
- Medium texture, herbaceous; green, blue-green
- Shape
- Upright, clumping
- Hardy in
- USDA zones 4 to 8
- Light
- Full sun
- Soil
- Average, well-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.