Plant List O
| Oenothera | "Crown Imperial" | A clump forming perennial with rich green leaves and heads of bright yellow flowers arising from red buds. Height 40-50cm. Moist well-drained soil in sun. Jun.-Aug. | |
| Oenothera | "Summer Sun" | A perennial "Evening Primrose" with red flushed leaves and clusters of red budded bright yellow flowers. Height 45cm. Well-drained soil in sun. | |
| Oenothera | ex "Colin Porter" | Lax stems of bright green leaves with terminal clusters of red flowers with a yellow edge. Height 15cm. Well-drained soil in sun. Jun.-Aug. | |
| Oenothera | ex "Lemon Sunset" | A perennial with narrow leaves on red stems topped with large fragrant lemon yellow flowers that age to dark pink. Height 90cm. Well-drained soil in sun. | |
| Oenothera | pilosella | "Yella Fella" | Dark green leaves, with white hairy undersides. Hairy stems carry many golden-yellow cup-shaped blooms, orange in bud. Height 40cm. Well-drained soil in sun. Jun.-Aug. Good autumn colour. |
| Olearia | macrodonta | "Minor" | An upright evergreen shrub with holly-like glossy, dark grey-green leaves and dense clusters of fragrant, daisy-like, white flowers with a reddish brown eye. Height 3m. Spread 2.5m. Well-drained soil in sun. Flowers from June to August. |
| Olearia | nummulariifolia | An evergreen rounded bush with leathery dark green whorls of tiny leaves and clusters of daisy-like, fragrant, white flowers in mid-summer. Height 2m. Spread 2m. Well-drained soil in full sun. July to August. | |
| Olearia | phlogopappa | "Combers Pink" | An evergreen upright bush with grey-green leaves, white-woolly beneath and clusters of daisy-like, pink flowers with a yellow centre. Height 2m. Well-drained sheltered site in sun. Jul.-Aug. |
| Olearia | x mollis | A compact rounded shrub with wavy-edged, silvery-grey slightly toothed leaves.Large corymbs of creamy white daisy flowers. Height 1m. Well-drained soil in sun. May. | |
| Olearia | x scilloniensis | "Master Michael" | An upright evergreen shrub with narrow grey-green leaves and small violet-blue daisy flowers. Height 1.2m. Spread 1m. Well-drained soil in sun. Flowers from April to May. |
| Olsynium | douglasii | Grass-like stems carry nodding bells of purple,pink or white flowers in early Spring. Dies down by June. Height 15cm. Moist soil in part shade. | |
| Omphalodes | cappadocica | "Cherry Ingram" | An evergreen perennial with lustrous leaves and pretty deep blue flowers. Height 20-25cm. Best in moist soil in part shade. March to April. |
| Omphalodes | cappadocica | "Starry Eyes" | An evergreen perennial with lush green ovate foliage and deep blue flowers and a central white stripe on each petal. Mar.-Apr. Height 25cm. Moist, fertile soil in part shade or dryer in full shade. |
| Omphalodes | verna | A semi-evergreen perennial with creeping stems and pretty bright blue flowers with a white eye in spring. Height 20cm. Moist soil in part shade. Mar.-May. | |
| Omphalodes | verna | "Alba" | A semi-evergreen perennial with creeping stems and white flowers. Height 20cm. Moist soil in part shade. Mar.-May. |
| Onoclea | sensibilis | Sensitive Fern. A deciduous fern with bold green triangular fronds, which emerge a pinky bronze colour. Height 60cm. Moist soil in part shade. good pond-side plant. | |
| Onosma | rigida | Neat mounds of narrow grey-green leaves and bearing nodding clusters of very lovely, tubular, light yellow flowers, each an inch or more long. Height 30cm. Well-drained soil in sun. May-Jun. | |
| Ophiopogon | japonicus | "Nippon" | Small tufts of arching green grass-like leaves bearing stalks of pink flowers followed by translucent blue-mauve berries. Height 10cm. Moist soil in part shade. |
| Ophiopogon | japonicus | "Tama-ryu" | Small tufts of arching deep green grass-like leaves bearing stalks of pink flowers followed by translucent blue-mauve berries. Height 5-10cm. Moist soil in part shade. |
| Ophiopogon | japonicus | "Variegatus" | Evergreen, clump-forming perennial with green, white edged leaves and lilac flowers in late summer. Height 25cm. Full sun in well-drained soil. |
| Ophiopogon | planiscapus | "Little Tabby" | A clump-forming evergreen perennial with narrow, curving, green, silver variegated leaves and clusters of white flowers . Height 15cm. Moist well-drained soil in part shade. Jul.-Aug. |
| Ophiopogon | planiscapus | "Nigrescens" | A clump-forming evergreen perennial with narrow, curving, almost black leaves. Clusters of pale purple flowers followed by almost-black fruit. Height 20cm. Moist well-drained soil in sun or shade. Jul.-Aug. |
| Origanum | "Barbara Tingey" | A dense evergreen subshrub with bluish green leaves and clusters of tubular pink flowers. Height 10cm. Well-drained soil in sun. Jun.-Sep. Probably best with winter protection. | |
| Origanum | "Buckland" | Arching stems of small grey-green leaves. Pinky mauve flowers within showy bracts. Height 15cm. well-drained soil in sun. Jun.-Aug. | |
| Origanum | "Dingle Fairy" | Upright stems of bright green leaves topped by mauve flowers. Height 20cm. Well-drained soil in sun. Jun.-Aug. | |
| Origanum | "Frank Tingey" | Upright stems with clusters of tubular pink flowers with pretty deep pink bracts. Height 20cm. Well-drained soil in sun. Jun.-Aug. | |
| Origanum | "Kent Beauty" | An evergreen subshrub with and clusters of tubular pink to mauve flowers with deep rose-pink bracts in summer. Height 10cm. Jun.-Aug. | |
| Origanum | "Nymphenburg" | An erect perennial with dark green leaves and clusters of dusky purple-pink flowers. Height 35cm. Well-drained soil in sun. May-Sep. | |
| Origanum | "Rotkugel" | An erect perennial with dark green leaves and clusters of large red mauve flowerheads. Height 50cm. Well-drained soil in sun. Jul.-Sep. | |
| Origanum | amanum | An evergreen subshrub with bright green leaves and clusters of long tubular pink flowers with pretty, green bracts flushed pink with age. Height 10-15cm. Well-drained soil in sun. Jun.-Sep. | |
| Origanum | calcaratum | An upright subshrub with grey leaves and erect spikes of pink flowers in summer. Height 30cm. Well-drained soil in sun. Jun.-Aug. | |
| Origanum | dictamnus | An evergreen subshrub with clusters of funnel-shaped pink flowers with purple bracts. Height 15cm. Sunny, well-drained spot. Protect from winter wet. | |
| Origanum | minutaeflorum | Tiny grey aromatic leaves with terminal clusters of purple-pink flowers. Height 15-20cm. Well-drained soil in sun. Aug.-Sep | |
| Origanum | vulgare | "Thumble's Variety" | A mound of golden green leaves and clusters of small tubular white flowers. Height 25cm. Sun in well-drained soil. Jul.-Sep. |
| Origanum | x hybridinum | A tufted perennial sub-shrub with downy grey-green leaves and clusters of pink flowers with pointed hop-like bracts. Height 25cm. Well-drained soil in sun. Jul.-Aug. | |
| Orixa | japonica | "Variegata" | A deciduous shrub with puckered leaves, shaded silvery-grey with a broad creamy white margin. Small greenish, pungently scented flowers are borne in panicles on old wood as the leaves emerge. Height and spread 2.5m. well-drained soil in sun or part shade. |
| Orthrosanthus | laxus | A clump forming perennial with strap-like leaves and spikes of flat six-petalled flowers. Height 30-40cm. Well-drained soil in sun. Jun.-Jul. Needs winter protection. | |
| Osmanthus | decorus | A dense evergreen shrub with glossy, dark green leaves and clusters of tubular white flowers. Height 3m. Spread 5m. Well-drained soil in sun or part shade. Flowers from April to May. | |
| Osmanthus | delavayi | A dense evergreen shrub with glossy, dark green leaves and clusters of tubular white flowers in mid-spring. Height 3m. Spread 5m. Well-drained soil in sun or part shade. April to May. | |
| Osmanthus | heterophyllus | "Goshiki" | A dense rounded shrub with holly-like, glossy, dark green, white and pink leaves, bronze when new, and clusters of fragrant tubular white flowers. Height 2m. Spread 2m. Well-drained soil in sun or part shade. Flowers from September to November. |
| Osmanthus | heterophyllus | "Purpureus" | A dense, upright, evergreen shrub with holly-like, glossy, leaves metallic purple when young and clusters of fragrant tubular white flowers. Height 2.5m. Spread 2m. Well-drained soil in sun or part shade. Flowers from August to September. |
| Osmanthus | heterophyllus | "Variegatus" | A dense, rounded, evergreen shrub with holly-like, glossy, dark green leaves variegated creamy white and clusters of fragrant tubular white flowers. Height 1.8m. Spread 1.8m. Well-drained soil in sun or part shade. August to September. |
| Osmanthus | x burkwoodii | A rounded evergreen shrub with glossy, dark green leaves and clusters of very fragrant tubular white flowers. Height 3m. Sun or part shade. Apr.-May. | |
| Osmanthus | x fortunei | An evergreen shrub of dense habit with large, broad, dark glossy green holly-like leaves and small white fragrant flowers. Height and spread 3m. Moist well-drained soil in sun or part shade. Flowers from August to September. | |
| Osmunda | cinnamomea | Related to the "Royal Fern", the emerging fronds are covered in white woolly hairs. Height 80cm. Moist soil in part shade. | |
| Osmunda | regalis | "Royal Fern". A deciduous fern forming dense clumps of dainty, thin, fleshy fronds that unfurl coppery-brown before turning green. Height 1.5m. Wet acid soils in dappled shade. | |
| Osmunda | regalis | "Cristata" | A flat crested form of the "Royal Fern". Deciduous with thin fleshy fronds opening coppery brown. cresting becomes more prominent in older specimens. Height 1-1.2m. Moist soil in part shade. |
| Osmunda | regalis | "Purpurescens" | "Purple Royal Fern". Larger growing than the type species with the young fronds unfurling a purplish colour and the stems staying purple throughout the season. Wet acid soils in dappled shade. |
| Osteospermum | "Lady Leitrim" | Hardy evergreen perennial with pale pink flowers from Apr-Sep. Height 30cm. well-drained soil in sun or part shade. | |
| Osteospermum | jucundum var. compactum | A compact neat, evergreen, clump-forming perennial with greyish green leaves and mauve-pink flowers with purple on the reverse and a purple eye. Height 20cm. Spread 60cm. Well-drained soil in sun. May-Sept. | |
| Ostrya | carpinifolia | A large rounded deciduous tree with toothed dark green leaves with pendulous yellow catkins in spring and pretty hop-like white fruit clusters in summer. Height 20m. Spread 20m. Well-drained soil in sun or part shade. | |
| Ourisia | macrophylla | A mat-forming, evergreen, perennial with bright green leaves and dense clusters of white flowers. Height 30cm. Moist soil in part shade. Jun.-Aug. | |
| Oxalis | "Ione Hecker" | A clump-forming perennial with clover-like grey-green leaves and pretty funnel-shaped, violet-blue flowers conspicuously veined dark purple. Height 8cm. Moist well-drained soil in sun. May-Jul. | |
| Oxalis | adenophylla | A clump-forming perennial with clover-like, grey-green leaves and funnel-shaped, pink flowers with a white centre. Height 10cm. Moist well-drained soil in sun. Apr.-May. | |
| Oxalis | depressa | A clump-forming perennial with clover-like, grey-green leaves, and pretty funnel-shaped, deep rose-pink flowers. Height 5cm. Well-drained soil in sun or part shade. Jun.-Aug. | |
| Oxalis | enneaphylla | A clump-forming perennial with clover-like blue-grey leaves and pretty funnel-shaped, light pink, fragrant flowers with purple veining. Height 8cm. Moist soil in sun or part shade. May-June. | |
| Oxalis | enneaphylla | "Sheffield Swan" | A clump-forming alpine with finely dissected blue-grey leaves and large funnel-shaped, white flowers. Height 8cm. Sunny spot on scree or Alpine House in well-drained soil. May-Jun. |
| Oxalis | imbricata | Deep rose-pink flowers over clover-like foliage. Height 8cm. Well-drained soil in sun. Oct.-Nov. Dormant throughout summer. | |
| Oxalis | lobata | Clump-forming with clover-like green leaves which appear in early spring, die down and reappear in autumn. Pretty funnel-shaped, bright yellow flowers. Height 10cm. Well-drained soil in sun. Aug.-Oct. | |
| Oxalis | palmifrons | Grown for its lovely leaves. Haven't seen it flower! Height 10cm. It gently spreads by bulbils. Gritty soil in Alpine house. | |
| Oxalis | purpurea | "Ken Aslet" | White hairy, dark green leaves and pretty, widely funnel-shaped bright yellow flowers. Height 10cm. Moist well-drained soil in sun. Sep.-Dec. |
| Oxalis | squamata | Deep pink flowers with a yellow eye over small grey-green clover-like leaves. Height 10cm. Gritty soil in full sun. Jun.-Oct. | |
| Oxalis | stipularis | Bulbous perennial with hanging flowers of pink with a white eye. height 15cm. Gritty soil in sun. Needs winter protection. May-Jul. | |
| Oxydendron | arboreum | A narrow deciduous tree or shrub with glossy, dark green leaves, turning brilliant shades of red, yellow and purple in autumn. Large clusters of white flowers. Eventual height 10-15m. Spread 8m.Moist well-drained acidic soil in sun or part shade. Flowers | |
| Oxytropis | megalantha | White hairy pinnate leaves, with spikes of blue-purple pea-like flowers. Height 20cm. Gritty well-drained soil in sun. May-Jul. | |
| Oxytropis | purpurea | Silver pinnate leaves, with spikes of purple pea-like flowers. Height 15cm. Gritty well-drained soil in sun. May-Jul. | |
| Oxytropis | shokanbetsuensis | A tufted perennial with grey pinnate leaves and heads of reddish purple flowers. Height 15cm. Gritty well-drained soil in sun. May-Jul. | |
| Oxytropis | splendens | Silky-grey pinnate leaves from a central rootstock. Short spikes of red-purple pea-like flowers. Height 20cm. Gritty well-drained soil in sun. Probably best in a greenhouse. Jun.-Jul. | |
| Ozothamnus | ledifolius | A compact, evergreen, rounded bush with yellowish green stems covered with narrow, dark green leaves and carrying clusters of white flowers. Height 1m. Spread 1m. Well-drained soil in sun..Flowers from June to July. |