Compass plant
Silphium laciniatum ·
Huge, deeply cut, leathery leaves that turn their edges north and south, and flower stems up to three metres tall with yellow daisies in late summer. It can live for a century.
- Size
- 8 ft tall, 3 ft wide
- Zones
- 3 to 8
- Light
- Full sun
- Flowers
- Mid July to early September
- Pets
- Not checked
- Job in a bed
- Specimen
A bed built around compass plant
The planner designed this bed around compass plant 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 compass plant stands where it does.
The plants
- 1 Compass plant × 1, yellow
- 2 Sea thrift × 11, pink
- 3 Winter heath × 11, white
- 4 Little bluestem 'The Blues' × 3, tan
- 5 Brown-eyed Susan × 3, yellow
- 6 Hardy gladiolus × 4, pink
- 7 Schubert's allium × 4, pink
Why this plant
- The only bold leaves here. The rest are fine and medium. A change of leaf keeps plants distinct when nothing is in flower.
Why here
- Anchors a back corner. At 8 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 little bluestem 'The Blues' (3 ft): no two neighbours there are the same height, so the back steps up and down like a skyline.
- One plant, alone. A feature plant is seen as an object, and needs clear ground around it.
Why now
- In flower for 9 weeks. From mid July to early September.
- Fills a gap. For two of those weeks nothing else on the plan is in flower.
Planned as an English border: 6 of the 7 groups (86%) are drifts, longer along the bed than they are deep. The scheme leans cool (pink) and uses yellow for warmth, with white and tan to calm things between them. Pink runs through the planting: 3 of the 7 kinds grown for their flowers have it. The Design check says heights needs revision.
The planner's own design check: 10 Excellent, 6 Good, 1 Needs revision. Its weakest point is height and scale: Heights average about 8 in at the front, 24 in in the middle and 4 ft at the back. Along the back row the heights step up and down, between 3 ft and 8 ft, and no two neighbours are the same height. 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 compass plant goes in a border
At 8 ft it belongs at the back of a bed. In the planner's ten height classes it is super tall (over 6½ ft).
Its job: specimen. A feature plant with a shape of its own. It stands alone with room around it, and repeats only at a distance.
The leaves are the most architectural of any prairie plant. It takes several years to flower and has a taproot as deep as the plant is tall, so place it once, with care.
- A towering accent in a prairie planting
- Sculptural foliage
- Large meadows
What to plant with compass plant
Plants recorded as good partners for it, and what each pairing does:
- Big bluestem: purple against yellow, opposite each other on the colour wheel, in flower together for four weeks; fine leaves against its bold ones.
- Rattlesnake master: in flower together for seven weeks, from mid July; low enough (4 ft) to stand in front of it.
- Pale purple coneflower: in flower together for two weeks, from mid July; medium leaves against its bold ones; low enough (3 ft) to stand in front of it.
Questions about compass plant
Does compass plant need sun or shade?
Compass plant 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 compass plant grow in?
USDA zones 3 to 8. It is hardy to zone 3, which means it survives winter nights down to about −30 °F (−34 °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 compass plant flower in my zone?
In zone 5 it flowers mid July to early September. As a summer flower it moves about half a week for every zone: earlier where it is warmer.
| Zone 3 | Mid July to early September |
|---|---|
| Zone 4 | Mid July to early September |
| Zone 5 | Mid July to early September |
| Zone 6 | Mid July to early September |
| Zone 7 | Early July to early September |
| Zone 8 | Early July to early 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 compass plant be planted?
2½ ft (75 cm) apart, from the middle of one plant to the middle of the next. That is a little closer than its full width of 3 ft (90 cm), so a group knits into one patch.
It grows 8 ft (240 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.
How many compass plant plants do I need?
At 2½ ft apart, set out in staggered rows:
- 2 to fill 10 square feet (about 1 m²)
- 5 for a single row 10 ft (3 m) long
- 6 to fill a 4 × 8 ft bed on its own
In a mixed border, plant it as one, with clear ground around it: a feature plant is seen as an object, and a group of them is a thicket.
In the bed above, the planner used one in one group.
Is there a native plant like compass plant?
Compass plant is not native to North America. These North American natives come closest to doing its job:
- Sweet Joe Pye weed: the same job in a bed and the same flowering time; 24 in shorter, 6 in wider.
- Hardy hibiscus: the same job in a bed and the same flowering time; 3 ft shorter, 6 in wider.
- Willowleaf sunflower 'First Light': the same job in a bed and the same colour; 4 ft shorter, flowers mid September to mid October.
Matched the way the planner's Swap button matches plants: the same job in a bed, then size, then flowering time.
What flowers after compass plant?
Compass plant is over by early September. These start as it finishes and carry the same spot on, so it never goes flat:
- Garden chrysanthemum: from mid September to late October, 24 in tall, to stand in front of it and cover its fading stems.
- Swamp sunflower: from late September to late October, 6½ ft tall.
- Korean feather reed grass: from late August to mid October, 4 ft tall, to stand in front of it and cover its fading stems.
What does compass plant look like in winter?
Compass plant 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 Silphium
- Cup plant Silphium perfoliatum
In these guides
Zone guides: Zone 3 · Zone 4 · Zone 5 · Zone 6 · Zone 7 · Zone 8
Every fact on record
- Type
- Perennial
- Size
- 8 ft (240 cm) tall, 3 ft (90 cm) wide
- Plant
- 2½ ft (75 cm) apart
- Height class
- Super tall (over 6½ ft)
- Place in the bed
- Back
- Flowers
- Mid July to early September; daisies; yellow
- Leaves
- Bold texture, herbaceous; green
- Shape
- Upright, clumping
- Hardy in
- USDA zones 3 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.