Romneya coulteri aka California Tree Poppy

Romneya coulteri belongs to the poppy family, Papaveraceae. Gardeners call it Matilija poppy or Californian tree poppy. Its native range runs from southern California into northern Baja California, Mexico. It grows in dry scrub and on land after fires. Kew classes it as a shrub. The RHS treats it as an herbaceous perennial. It loses its leaves and sends up suckers.

Garden plants reach about 5–8 feet [1.5–2.5 metres] tall. Their spread reaches about 3–5 feet [1–1.5 metres]. The RHS also describes plants around 6.6 feet [2 metres] tall. Plants take five to ten years to reach full size. The divided leaves have a grey-green tone. Large white flowers stand out against this foliage. Each bloom can span about 0.5 feet [0.15 metres]. Crinkled petals surround a dense centre of deep yellow stamens. These broad flowers give the plant much of its garden value.

Choose full sun and a spot sheltered from cold winds. The RHS recommends a warm wall as a planting site. South-facing or west-facing sites suit its needs. It grows in sandy or loamy soil with good drainage. Acid, neutral and alkaline soils all suit it. Soil can stay moist, provided excess water drains away. Established plants resist drought. The RHS gives it a UK hardiness rating of H5. This covers minimum temperatures from about −15 to −10°C. The RHS also advises a deep mulch before winter.

This plant suits cottage gardens and loose, informal planting schemes. It also fits Mediterranean-style gardens and borders beside walls. Choose its place with care before planting. It dislikes being moved, yet established plants can spread through suckers. Allow for this spread when placing it near other plants. Its height and wide flowers suit a border with room. The need for shelter also helps guide its garden position.

Caterpillars can cause trouble, and powdery mildew may occur. These are the pest and disease problems listed by the RHS. For propagation, take basal cuttings in spring or root cuttings in winter. Seeds can also be sown in spring. The RHS specifies 13–16°C for seed sowing. The supplied sources give no evidence of edible parts. They also provide no assessment of human or pet toxicity.