Jacob's ladder
Polemonium caeruleum ·
Clusters of cup-shaped, lavender-blue flowers with yellow stamens stand above ferny leaves, whose paired leaflets look like the rungs of a ladder.
- Size
- 24 in tall, 18 in wide
- Zones
- 4 to 8
- Light
- Part sun to part shade
- Flowers
- Mid May to late June
- Pets
- Not checked
- Job in a bed
- Drift
A bed built around Jacob's ladder
The planner designed this bed around Jacob's ladder when this page was made: a 12 × 6 ft (3.7 × 1.8 m) cottage garden in zone 6, part sun. It chose the other plants from the 708 that suit those conditions, and says below why Jacob's ladder stands where it does.
The plants
- 1 Jacob's ladder × 5, blue
- 2 Mouse-ear coreopsis 'Nana' × 14, yellow
- 3 Creeping mahonia × 6, yellow
- 4 Garden phlox 'David' × 3, white
- 5 Bee balm 'Purple Rooster' × 3, purple
- 6 Dwarf English boxwood × 1, dark green leaves
- 7 Crocosmia 'Emily McKenzie' × 3, orange
- 8 Meadow saffron × 5, pink
Why this plant
- The only bells. The others are daisies, dense clusters, globes and others. Shape reads at a distance, where colours blur.
- The only blue.
Why here
- In the middle. At 24 in it is seen over creeping mahonia (12 in) in front of it.
- A step in the back row. Next to dwarf English boxwood (2½ ft) and garden phlox 'David' (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 7 weeks. From mid May to late June.
- Fills a gap. For one of those weeks nothing else on the plan is in flower.
Planned as a cottage garden: 32 of the 32 plants (100%), bulbs aside, stand alone or in groups of no more than five, small enough for the kinds to mingle. The bed is balanced: the left half carries 47% of the visual weight and the right half 53%. There is more mouse-ear coreopsis 'Nana' than anything else, 14 plants in all.
The planner's own design check: 12 Excellent, 5 Good.
Open this bed in the planner Change its size, the sun or the style, move plants about, or swap one for another.
Where Jacob's ladder goes in a border
At 24 in it belongs in the middle of a bed. In the planner's ten height classes it is medium short (18 to 24 in).
Its job: drift. Planted in a small group of three or five, and repeated further along in the other number.
It needs cool, moist soil and suffers in hot summers. Cut it back after flowering for fresh leaves and fewer seedlings.
- Blue for part shade in early summer
- Cottage and woodland gardens
- Ferny foliage
What to plant with Jacob's ladder
Plants recorded as good partners for it, and what each pairing does:
- Bleeding heart: in flower together for four weeks, from mid May; happy in the same moist soil.
- Hosta: its green leaves are a setting for the flowers, before and after; bold leaves against its fine ones; happy in the same moist soil.
- Lady's mantle: in flower together for five weeks, from late May; happy in the same moist soil.
Questions about Jacob's ladder
Does Jacob's ladder need sun or shade?
Jacob's ladder grows in part sun (4 to 6 hours of sun, including some afternoon sun) and part shade (2 to 4 hours of sun, mostly in the morning).
It wants soil that stays evenly moist, rich in organic matter, and a good soak in dry spells.
What zones does Jacob's ladder 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 Jacob's ladder 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 early July |
|---|---|
| Zone 5 | Mid May to late June |
| Zone 6 | Early May to late June |
| Zone 7 | Early May to late June |
| Zone 8 | Late April to late 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 Jacob's ladder 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 24 in (60 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.
How many Jacob's ladder 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.
Will Jacob's ladder spread?
It seeds itself about; the risk of it taking over is moderate. Self-seeds freely. Remove the spent flowers to limit seedlings.
What flowers after Jacob's ladder?
Jacob's ladder is over by late June. These start as it finishes and carry the same spot on, so it never goes flat:
- Astilbe: from late June to mid July, 24 in tall.
- Black-eyed Susan: from mid July to mid September, 24 in tall.
- Daylily: from late June to early August, 2½ ft tall.
What does Jacob's ladder look like in winter?
Jacob's ladder 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 Polemonium
- Creeping Jacob's ladder Polemonium reptans
- Jacob's ladder 'Stairway to Heaven' Polemonium reptans 'Stairway to Heaven'
In these guides
Every fact on record
- Type
- Perennial
- Size
- 24 in (60 cm) tall, 18 in (45 cm) wide
- Plant
- 16 in (40 cm) apart
- Height class
- Medium short (18 to 24 in)
- Place in the bed
- Middle
- Flowers
- Mid May to late June; hanging bells; blue, white
- Leaves
- Fine texture, herbaceous; green
- Shape
- Upright, self-seeding
- Hardy in
- USDA zones 4 to 8
- Light
- Part sun, part shade
- Soil
- Rich, evenly moist
- Water
- Moderate
- Feeding
- Light, in spring
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.