Compass plant Silphium laciniatum
Compass plant (Silphium laciniatum) is a deciduous perennial flowering plant in the Asteraceae family, native to Tallgrass prairies of the central United States. It grows 1.5–3 m (4.9–10 ft) tall and 60 cm–1 m (24 in–3.3 ft) wide, wants full sun and low water, and is hardy to about -35 °C (-31 °F). Space plants about 80 cm (31 in) apart.
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Compass plant at a glance
| Type | Perennial flowering plant, deciduous |
|---|---|
| Family | Asteraceae |
| Mature height | 1.5–3 m (4.9–10 ft) |
| Mature spread | 60 cm–1 m (24 in–3.3 ft) |
| Spacing | 80 cm (31 in) centre to centre |
| Sun | Full sun, at least 7 h of direct sun a day |
| Water | Low; drought tolerance high, waterlogging tolerance none |
| Soil pH | 6–8 |
| Cold hardiness | About -35 °C (-31 °F) once established (roughly USDA zone 3) |
| Heat stress | Likely above about 38 °C (100 °F) |
| Flowering | from about July for 6–9 weeks (northern hemisphere; later in cold climates, earlier in warm ones) |
| Wind tolerance | Moderate |
| Pollinator value | High |
| Edible | Not grown as food |
| Native to | Tallgrass prairies of the central United States |
| Common in gardens of | 🇺🇸 United States, 🇨🇦 Canada |
Is Compass plant toxic?
- People: not known to be toxic
- Cats: not known to be toxic
- Dogs: not known to be toxic
Not known to be poisonous.
If a child or pet may have eaten part of a plant, call a poison centre or vet straight away.
Companion planting: what to grow with Compass plant
No well-documented helpful pairing. Group it with plants that like full sun and low water.
Questions about Compass plant
- How far apart should I plant Compass plant?
- About 80 cm (31 in) apart, centre to centre. A mature plant spreads 60 cm–1 m (24 in–3.3 ft).
- Does Compass plant need full sun?
- Full sun: at least 7 hours of direct sun a day.
- How much water does Compass plant need?
- Low water. Drought tolerance is high and waterlogging tolerance none.
- How cold-hardy is Compass plant?
- It tolerates about -35 °C (-31 °F) once established, roughly USDA zone 3.
- When does Compass plant flower?
- From about July for 6–9 weeks (northern hemisphere; later in cold climates, earlier in warm ones).
- Is Compass plant poisonous to cats and dogs?
- For cats it is not known to be toxic; for dogs not known to be toxic; for people not known to be toxic. Not known to be poisonous.
- What grows well with Compass plant?
- There is no well-documented companion pairing for Compass plant. Group it with plants that like the same sun (full sun) and water (low).
Sources and evidence
Evidence grade A (A: strong evidence).
- Plants of the World Online (taxonomy, native range), Royal Botanic Gardens, Kew
- Missouri Botanical Garden Plant Finder, Missouri Botanical Garden
- Illinois Wildflowers (descriptions and insect-visitor records), John Hilty, illinoiswildflowers.info
Notes and assumptions
- A tallgrass prairie plant: deep roots make it drought-proof once established; it wants sun and lean soil (rich soil makes it flop). Leave the stems standing in winter for seed-eating birds and overwintering insects.
- Huge, deeply cut basal leaves that turn their edges north–south to avoid the midday sun, so settlers used them as a compass; tall stems of yellow sunflower-like flowers rise above in summer. Its taproot can go 4 m deep; slow to establish but lives for decades.
Reference values for planning, not horticultural, veterinary or medical advice. Varieties, soils and local climates differ: check with a local nursery or extension service.
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- Black-eyed Susan Rudbeckia hirta
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