Clematis x cartmanii 'Avalanche' is a valuable evergreen clematis, derived from two New Zealand species, and has the largest flowers in its group. The 7.5cm (3in) pure white blooms, opening in March and April, can almost completely obscure the fresh green foliage and as a specimen in a large container it’s unbeatable. I’ve also seen it thriving on a sunny fence and tumbling over a low wall, but it appreciates shelter and good drainage. 1.8m (6ft).
With flowers of attractive simplicity and charming colour, Clematis 'Frances Rivis' has four broad, arching outer petals, that are often attractively waved or twisted, in clear mid blue. In the centre is a boss of slender white petals, which are sometimes a little blue-tinted. Opening in April and May, the 5-7.5cm (2-3in) flowers are followed by fluffy seedheads. Selected from plants grown from wild-collected seed. 2.4m (8ft).
Named for the award-winning actress Constance Cummings, the 5cm (2in) long flowers of Clematis 'Constance' are semi-double variety are a bright purplish-pink. The extra petals provide increased impact and the pale green foliage shows off the flowers well. Blooming in April and May, 'Constance' is also more prolific than most varieties. Like many of this type, it is derived from both Clematis alpina and C. macropetala. 2.4m (8ft).
Clematis 'Frankie' is another very elegant, blue-flowered cultivar for April and May which is paler than 'Frances Rivis'. The pale violet-blue outer petals sometimes feature a slight bronze haze while the white inner petals are tinted and tipped with the same shade of blue. They often flare rather like the flowers of a double Campanula; there is just a little scent. Raised in Lincolnshire by Frank Meecham. 2.4m (8ft).
Clematis cirrhosa var. purpurascens 'Freckles' is an unusually striking variety of an evergreen Mediterranean species, selected by RHS Council member Raymond Evison. The inside of each nodding, creamy yellow flower is heavily patterned in purplish-red and has a citrus scent. Flowering can be in autumn, as well as winter and spring – depending on the season – and the slightly ferny foliage is attractive for the rest of the year. 2.4m (8ft).
Flowering in late April and May, Clematis 'Helsingborg' is distinctive in two ways. Firstly, the inner cluster of petals is often the same mauve-blue shade as the larger, flared outer petals that are also paler at the edges and tend to turn up attractively at the tips. Secondly, each 6cm (2in) flower is carried on a dark, bronze-red stem. All is set off against pale green foliage. 2.4m (8ft).
Harmony in pink
One of the finest of all spring flowering deciduous cultivars, Clematis 'Jacqueline du Pré' features large, 6cm (2-3in) flowers in bright rosy pink, each outer petal edged in silvery-white, in late April and May. 'Jacqueline du Pré' presents its flowers unusually well, sometimes turning up and flaring widely to show off the pink inner petals. Raised by clematis breeder Barry Fretwell and named for the famous cellist. 2.4m (8ft).
The wide flowers of Clematis macropetala 'Lagoon', up to 7.5cm (3in) across, open from mid-April to mid-May. They have four to six long outer petals in violet blue then, inside, about a dozen more petals in the same shade creating a star-like effect. Combined with the flower size and the plant’s general vigour, 'Lagoon' stands out among the many blue flowered varieties. 2m (6½ft).
Pretty in pink
Delicately veined in pink, and with a richer pink zone towards the base of the petals, the balance of colours in the semi-double flowers of Clematis 'Pink Flamingo' varies slightly with maturity and growing conditions. Flowering in April and May, often with a second flush in July and August, the intriguing patterning of the flowers repays close inspection so plant near a door or an arch over a path. 2.4m (8ft).
Noticeably the best of the white-flowered deciduous spring clematis, the nodding blooms of Clematis 'White Columbine' are pure white and the inner petals, in their tight cluster, are tipped with green. Blooming in April and early May, the combination of the pristine flowers and the pale, fresh green foliage makes 'White Columbine' ideal for growing through dark-leaved shrubs such as purple-leaved berberis. First awarded the AGM more than 20 years ago. 2.4m (8ft).