Sedum has been used in mixed borders for years. But these days they are often selected as a vital part of green roof mats. They are popular for this because the low-growing, hardy species used can withstand many different weather conditions.
The genus, in the family Crassulaceae, includes 300 species of usually succulent, annual to perennial herbs and sub-shrubs. They can be found in a wide range of habitats including marshland, desert and alpine regions. A few are epiphytic, growing on trees.
The majority are frost-hardy, withstanding temperatures down to -15 degsC. An exception is S. spurium, which only tolerates temperatures down to -5 degsC. A number of species need protection from frost and are best grown as house or glasshouse plants because they need a winter minimum of 5 degsC.
The border plants are the taller Sedum, such as S. 'Herbstfreude' (syn. S. 'Autumn Joy') or S. spectabile 'Brilliant' Award of Garden Merit (AGM), which have thick stems and fleshy leaves. Sedum flowers appear in autumn and tend to be in shades of pink and mauve that start out pale and deepen as they mature, but can also be white, yellow, red and rarely blue. They prefer being sited in full sun, fertile, well-drained soil.
Smaller hardy types such as S. acre, S. oreganum and S. album are more suitable in scale for the rock garden and are commonly grown there or in the alpine house. These are the types being used on green roofs. They are planted into mats of polyester or hessian in a thin layer of growing medium, often with several varieties of Sedum or with grasses and herbs.
Generally, the varieties used on green roofs are just left to increase and require little maintenance. In the border, however the stems are cut down annually. Some gardeners cut them down after flowering, in late autumn, but others prefer to leave the flower heads on over winter as a feature. They should then be cut back in February and March, and a mulch applied.
To prevent heavy stems flopping over, the "Chelsea chop" can be used. This involves cutting one in every three stems down to the ground in the last week of May. The plant will be less lush and will flower later.
Sedum look effective planted en masse at the front of a border in a scheme that needs autumn interest. They are also useful as specimen plants and are great cut flowers. Their attractiveness to birds and butterflies means that they are an asset in wildlife gardens.
Propagate large perennials, sub-shrubs and shrubs by soft wood cuttings or by division in spring and early summer, or by seed. Other species are propagated from stem cuttings, leaf cuttings or offsets. Plants are subject to attack by aphids and mealybug. Outdoor plants may need protection from slugs.
WHAT THE SPECIALISTS SAY
Robin Pearce, partner, World's End Garden Nursery, Worcestershire "Sedums have interesting foliage in the winter once the flowers have died away. They are excellent for birds, which take away their seeds in winter, and they are fantastic for attracting butterflies. They are generally trouble-free plants, though they do sometimes get vine weevil.
"There are lots of good dark varieties, including S. 'Autumn Joy', which is a great standard plant. A good one that sold well last year was 'Mr Goodbud' — a dwarf, more compact version of 'Autumn Joy'. It has similar coloured flowers but smoky green foliage.
"One that does well in the garden is S. 'African Pearl'. It has dark red foliage, pink flowers and is not too tall. The taller varieties tend to fall over and stems break off. Another variety that has also done well recently is S. 'Jose Aubergine', with aubergine coloured foliage and rose pink flowers."
Kevin Marsh, grower, Beeches Nursery, Essex "Their key selling point is that they are autumn flowering and are easy to grow. Sadly, in the past year Phoma has affected many Sedum grown by commercial nurseries. It was also seen at the Wisley Sedum trial.
"It is spread when water splashes up and causes holes to be burned into the leaves, leading to disfigured plants. To treat them you need to disinfect the area and cut the stems down before they have flowered. It's really emerged this year and is generally spread by overhead watering systems.
"There is a lot of breeding going on. The public particularly like brown-leaved varieties. Breeders are concentrating on hybrids of S. telephium. The ice plant, S. spectabile AGM, is not so popular anymore because they tend to split in the middle. Of the dark leaved varieties, S. 'Purple Emperor' stands out. It has purple flowers and brown leaves. Then there is 'Postmans Pride', with burgundy red flowers and dark brown/purple leaves. The green leaved 'Mr Goodbud' flowers profusely, with masses of flowers borne on branched heads."
Dan Bowyer, director, Fisher Tomlin, London "It's great to use in living walls and on green roofs, particularly the smaller species such as S. oreganum. I haven't used it yet on a roof but we are currently designing a green wall for a commercial project in which it is included alongside Heuchera and Euphorbia. It will survive as long as it is well irrigated, and therefore irrigation will be built into the living wall.
"But Sedum is also useful throughout garden schemes, mainly as a front of border plant, planted densely. It provides good structure and its foliage is a contrast against blowsier flowery plants."
SPECIES AND CULTIVARS
- S. 'African Pearl' is a short variety, reaching just 25cm. It has fleshy brown-red foliage and tiny pink flowers from August to October.
- S. 'Bertram Anderson' AGM has prostrate purple-black foliage, with plants only reaching 20cm. It bears maroon plates of tiny flowers from July to September.
- S. 'Carl' has grey-green foliage and flat plates of tiny rose-pink flowers from August to October. Height 45cm.
- S. erythrostictum 'Frosty Morn' has grey-green foliage with white margins and pale pink, almost white flowers from late summer to early autumn. Height and spread, 50cm.
- S. 'Herbstfreude' AGM (syn. S. 'Autumn Joy') is arguably the best known cultivar of Sedum. It has light green, succulent leaves and pink flowers in the summer and autumn, fading later to chocolate brown. Height and spread, 60cm.
- S. 'Jose Aubergine' Plant Breeders' Rights (PBR) is from the same breeder as S. 'Postman's Pride', Jose De Buck, chairman of the Flemish Perennials Association and sometime postman. As its name suggests, its foliage is aubergine coloured. Tiny rose-pink flowers are borne from July to September. Height, 60cm.
- S. 'Joyce Henderson' has large purple flushed foliage and plates of tiny pink flowers from August to October. Height, 70cm.
- S. 'Matrona' AGM has large, succulent leaves that vary from pigeon-grey to smoke-purple. The flowers are soft pink and borne from August to October. Height, 45cm.
- S. 'Mr Goodbud' AGM (PBR) is a short variety, with height and spread of 30cm. It has smokey blue-green leaves and bears tiny dark mauve flowers profusely from late summer through to autumn.
- S. 'Ruby Glow' AGM has greenish-purple leaves, topped with large, flat heads of ruby-red, star-shaped flowers from mid-summer to early autumn. Height, 30cm. Spread, 50cm.
- S. spectabile AGM is also known as the ice plant. Features grey-green leaves and flat heads of pale pink flowers from late summer to autumn. Height and spread, 45cm.
- S. spectabile 'Brilliant' AGM has grey-green leaves, topped with large, flat heads of bright pinkish-mauve flowers in summer. Height and spread, 45cm.
- S. spectabile 'Iceberg' bears pure white plates of tiny flowers from August to October. Height, 60cm.
- S. telephium 'Postman's Pride' (PBR) is a compact, bushy type with deep purple succulent leaves. Keeps uniform dark colouration, unlike parent 'Purple Emperor', which can "green up" in shade. In late summer and autumn it produces short inflorescences of flower buds the same colour as the foliage. The flowers are pink-tinged purple and age to a darker burgundy colour. Height and spread, 40cm.
- S. telephium 'Purple Emperor' AGM has deep purple, almost black succulent foliage, topped with red-purple flower heads from August to October. Height and spread, 45cm.
- S. telephium 'Strawberries and Cream' has grey-green foliage gaining a bronze tint with age, and above pale red and white flowers from July to September. Height, 35 cm.
- S. 'Vera Jameson' AGM has prostrate purple foliage and pink flowers from August to October. Height, 25cm.