Matilija poppy

Sun

Full sun; choose a warm, sheltered position in cooler climates.

Water

Water deeply but infrequently while establishing, allowing the soil to dry between waterings. Established plants usually need little additional water in dry-summer climates.

Soil

Well-drained sandy, gravelly or loamy soil; tolerates poor soil and some clay if drainage is good. Avoid sites that remain wet in winter.

Height

6-8 ft (1.8-2.4 m)

Spread

6-10 ft (1.8-3 m), eventually wider where underground stems are not contained

Flowers

Late spring through summer; large white flowers with prominent golden-yellow centres.

Foliage

Deeply lobed, blue-grey leaves on upright stems; deciduous in colder areas and partly evergreen in mild climates.

Growth

Often slow to establish, then vigorous and spreading.

Care needed

Medium

• Pollinators
• Deer resistant
• Drought tolerant
• Heat tolerant
• Low allergen
• Fragrant

Northern hemisphere months. In Australia, shift them by six.

Difficulty

Hard

Toughness

Needs looking after

Pick your zone, country, light and whether you have pets.

1. Planting day

   1 ft (0.3 m)

2. After 1 year

   3 ft (0.9 m)

3. After 2 years

   5 ft (1.5 m)

4. After 3 years

   7 ft (2.1 m)

   full size

About 3 years to full size.

From a typical nursery size, at an average rate for this kind of plant. A rule of thumb, not a forecast.

Cats and dogs

Toxic

Native to

the US

In the garden

Spreads vigorously: plan to contain it.

Growth rate

Moderate

• Plant small, container-grown plants without breaking up or teasing out the rootball; roots resent disturbance.
• Water deeply during establishment, then reduce watering as new growth becomes strong.
• Avoid routine feeding, especially high-nitrogen fertiliser, which encourages excessive leafy growth.
• Keep mulch away from the crown; use gravel rather than a thick, moisture-retaining organic layer on damp sites.
• Remove unwanted suckers promptly, digging out their connecting underground stems where practical.

Pruning. In late winter or early spring, cut old stems back to about 6-12 in (15-30 cm), taking care not to damage emerging shoots. In frost-prone gardens, leave old stems standing through winter and prune as new growth begins.

Late winter

Check that winter rain drains freely and remove debris resting against the crown.

Early spring

Cut back old stems as fresh shoots appear.

Spring

Plant in cooler climates after severe frost has passed, keeping the rootball intact.

Late spring

Check the edges of the clump and remove suckers growing into paths or neighbouring plants.

Summer

Water young plants deeply during prolonged dry weather; avoid frequent watering of established clumps.

Autumn

Plant in mild, dry-summer climates once rain returns, provided the soil drains well.

• Use at the back of a broad, sunny border, where tall stems and large white flowers rise above lower planting.
• Plant on a dry bank or spacious informal slope where spreading colonies are welcome.
• Combine with lavender, sage and low ornamental grasses for a silver-leaved, dry-garden planting.
• Use as a bold seasonal feature in a California-native garden, away from small plants it could overwhelm.

Garden styles it suits: California native, Mediterranean, Dry gravel garden, Desert / xeriscape, Coastal and White garden.

Plant it with: California sagebrush, Purple sage, California buckwheat, Lavender, Santolina and Deer grass.

Wildlife: The pollen-rich flowers attract bees and other pollen-feeding insects. They offer little or no nectar.

• Poor establishment after planting: use a young plant, leave its roots undisturbed and water carefully through its first growing season.
• Crown or root rot in wet soil: improve drainage or replant on a raised mound; do not keep the crown constantly damp.
• Unwanted spreading: remove suckers and their connecting underground stems repeatedly; avoid planting beside delicate borders.
• Frost-damaged stems: leave them until early spring, then cut back to healthy growth; protect the root zone in colder gardens.

Not a food plant: its alkaloid-containing tissues may be harmful if eaten, and sap may irritate skin. Reliable species-specific information on poisoning severity in people, cats, dogs and horses is limited; prevent ingestion and wear gloves when cutting stems.

Where it spreads. Can spread aggressively by underground stems in gardens in California and other mild regions, including parts of the UK and southern Australia. Allow substantial space and keep it away from boundaries where suckers would be difficult to remove; this garden-spreading behaviour does not by itself indicate an official invasive listing.

• Bristly Matilija poppy (Romneya trichocalyx)

  Very similar in flower and habit, but its flower buds have conspicuously bristly sepals; those of Romneya coulteri are essentially hairless.

• Crested prickly poppy (Argemone polyanthemos)

  Also has crinkled white flowers and grey-green leaves, but the leaves, stems and seed capsules are conspicuously prickly.

• Oriental poppy (Papaver orientale)

  Forms a lower clump of hairy leaves with individual flower stalks, rather than tall, branching, woody-based stems with smooth blue-grey foliage.

Romneya honours Irish astronomer Thomas Romney Robinson, while coulteri honours Irish botanist Thomas Coulter.

Propagation. Take root cuttings during dormancy, using healthy root sections and a free-draining medium. Rooted suckers can also be lifted carefully, but transplanting is unreliable because the roots dislike disturbance. Seed germination is erratic and may require specialist smoke or heat treatment.

Accepted botanical name

Romneya coulteri

In the US and Canada

Native in the lower 48 states.

Native range

California and Mexico Northwest.

Sources: GBIF (CC BY 4.0), USDA PLANTS and Trefle (CC BY 4.0). The care and design notes are LandscapeGPT's own.