The genus Clematis is found within the family Ranuculaceae along with other garden favorites such as Helleborus, Paeonia, Anemone and Thalictrum.  Currently there are over 300 recognized species of Clematis found all over the world but predominantly in the more temperate regions of the Northern Hemisphere.  To help clarify the situation many taxonomists will subdivide the genus into groups or subgroups according to species or growth habit.  The stereotypical Clematis is a climbing vine with large colorful flowers, usually appearing in mid summer. These are usually known as the ‘large flowered hybrids’ and there are, by conservative estimates, over 700 cultivars available.  But there is so much more to this genus than just the well-known vines with their beautiful, large, open blooms.

Most of the species have 'small' flowers, many of which are bell shaped and nodding, and generally what they lack in size, they make up for in abundance.  In addition the use of a variety of small flowering, or species type selections, along with the large flowered hybrids enables the gardener to have Clematis in bloom in the garden from early spring through to a hard killing frost.  Many of these plants are not easily recognized as Clematis, as they are so far removed from the stereotype in flower timing, shape and/or growth habit.  A lot of fun can be had convincing visitors that a particular plant is, indeed, a Clematis.

There are three basic growth habits for these plants, not all of them are climbers.  Those that do climb, do so by way of spiraling their petioles around any convenient twig, branch, wire or trellis and hauling themselves up into the sunshine.  As they are not self clinging they must be provided with some mechanism upon which to climb.  FYI, this does not have to be a trellis placed against a wall – Clematis are quite happy to climb through large shrubs or small trees, will not harm the host plant, and provide many opportunities for companion planting.  Alternatively there are the non-climbing types; some act as herbaceous perennials, with fairly short stems that generally die to the ground with cold weather, only to re-emerge in the spring, and others that, while attaining the length of stem that could be called vine-like, do not possess the ability to twine and thus cling and climb.  These will act more as scramblers and ground covers.

The early blooming species are C. alpina, and C. macropetala which have nodding flowers and just a little later C. montana which has the more open form most associated with Clematis, but somewhat smaller than the large hybrids.  C. alpina, C. macropetala and their many cultivars and selections are hardy to USDA zone 3 to 8, while C. Montana, although one of the most fragrant species, is not as tough, being reliable to USDA 6 for flowers and USDA 5 for the plants themselves.  As the summer moves along species such as C. integrifolia, C. heraclifolia (both strictly herbaceous), C. texensis (one of the few species to carry the gene for red flowers) and C. tangutica (carrying genes for yellow flowers) bloom in a predictable succession.  By late summer and into autumn the garden is graced by the flowering of C. viticella and C. terniflora (the sweet autumn Clematis which generally needs a good hard frost to put it to bed for the season).  There are named selections and cultivars of many of these species, but when plant breeders started mixing the species and producing complicated crosses the world of Clematis really started to get interesting.  Each species brings something different to the party and the offspring are often varied and usually interesting.  

The very first large flowered hybrid Clematis to be released to the retail trade appeared in 1858, it is still available today, and still extremely popular – C. 'Jackmanii'.  The exact parentage is thought to be predominantly C. viticella with some C. integrifoila mixed in for good measure.

Knowing the heritage of individual plants allows the grower to make educated decisions regarding care, placement and pruning.  The plants that bloom before the middle of June generally will have more early flowering species in their ancestry and are blooming on 'old wood'.  That is to say the flower buds are formed the previous summer and fall.  An early spring pruning will remove these buds and hence diminish the floral display.  Conversely those plants that first bloom after mid June (or thereabouts) claim more C. viticella in their family tree and are most likely flowering on new growth. Therefore these later bloomers can have their display enhanced by a significant pruning before growth starts in the spring.  Proper pruning of Clematis continues to be one of the most anxiety causing dilemmas of the home, and often professional, gardener.  By thinking of them as flowering shrubs, rather than exotic vines, this concern could be eased, just as Forsythia and Lilac are best pruned after the flowers fade, so too the early spring flowering Clematis.  But if the shrub/Clematis flowers in the fall, early pruning is an excellent idea.

An additional note of interest: the petals and sepals are indistinguishable from each other and so are referred to collectively as tepals.  Once the floral display has finished these plants continue the show with lovely interesting seed heads.  In general, Clematis prefer a sunny location but would prefer a cooler area for their root zone.  Simply providing some shade at the planting site is normally sufficient.  Since Clematis must have viable buds from which to sprout it is always a good idea to plant them deep,  i.e. bury at least 2 nodes underground when planting.  This provides for some insurance against mice, soccer balls and weed-eaters.

C. integrifolia:  

A beautiful herbaceous perennial, suitable for placement in the mid- to foreground of the border.  This true species is grown from seed and thus can exhibit quite a bit of variability in size and form.  Some specimens are quite compact and upright in habit while others have elongated stems that have a definite relaxed inclination.  All have exquisite, urn shaped nodding flowers borne singly on long petioles, in early summer to early fall.  Traditionally blue, but occasionally white or pink blooms appear.  A full sun location is preferred, with regular moisture but well drained soil.  No Clematis can handle ‘wet feet’.  As with all herbaceous Clematis, this species dies to the ground with the advent of winter weather, and reappears in the spring.  Obviously no pruning is necessary except to tidy the dead stems. Height: 1.5’ to 3’ (45 cm to 100 cm).   Spread: 2’ to 3’ (60 cm to 100 cm).  USDA: 3 to 7.

C. ‘Arabella’:  

Released in 1994 this selection of the integrifolia group is an amazing, long blooming cultivar with beautiful azure blue flowers held in the more traditional open manner.  In addition the anthers are a lovely contrasting cream color which gives an appearance of variegation from a distance.  Since this is an integrifolia, ‘Arabella’ does not climb or cling but will scramble through the garden or can be supported by neighboring plants to keep it more upright.  The masses of bloom provide for almost continuous color June through October that cannot fail to add a presence to any garden. Height: 4.5’ to 6’ (1.5m to 2m).  Spread: up to 5’ (180 cm).  USDA: 4 to 9.

C. ‘Fascination’ PP14770:  

Also in the integrifolia group but this 2003 release bears more of a resemblance to the species than 'Arabella', but with a larger growth potential.  The nodding, bell shaped flowers are deep violet with a contrasting lavender edge.  The tepals are conspicuously recurved to reveal prominent yellow anthers.  Dependable bloom from June through August.  Non-clinging but a beautiful herbaceous addition to any garden.  Height: 4' to 5' (120cm  to 180cm)  Spread: about 4' (120 cm)  USDA 3 to 9.

C. recta 'Purpurea':

An unusual and underused selection.  Also an herbaceous, non-climbing species, but definitely an asset to any display.  Early spring sees the deep purple foliage emerging on purple stems.  This wonderful color does mature to a deep green as the summer progress but the contrast is amazing as the world is coming back to life.  Fragrant, white flowers are abundant in late spring to mid summer.
The plants may need some support to remain upright but look amazing sprawling through the beds. Height: 2' to 4' ( 30cm - 60 cm)  Spread: 2' to 4' (30cm – 60 cm)  USDA 3 to 9.

C. texensis 'Princess Diana':

The texensis group are later bloomers, saving their show for August through October (frost permitting).  This relatively new selection has the most amazing, electric pink, tulip shaped flowers that are held upright in great abundance.  Texensis species will climb but are equally at home scrambling through the border, draping over a wall, or starring in a container.  'Princess Diana' has impressed all who have grown her and is sure to become a favorite of those who are yet to have the pleasure.  Height: 8' (90cm)  Spread: 4' (120 cm)  USDA 3 to 9.

C. 'Piilu':  

The only 'large flowered hybrid' in this discussion, this beautiful plant is quite unusual and one of the many 'must have' selections.  4” (10cm) wide double flowers appear in May and June in great abundance.  The tepals are deep pink with a central bar of reddish purple.  The tepals toward the center of the flower are smaller than those towards the outside giving almost a 'pom-pom' effect.  These early blooms appear on 'old growth'.  But the show isn't over in June.  Later in the summer 'Piilu' blooms again – this time with single flowers!  These new growth flowers appear in August – September.  The plant was hybridized in Estonia and the name 'Piilu' translates to 'Little Duckling'. Relatively short in stature it is suitable for containers or climbing a support.  Height: 6' (2m)  Spread: 3' (1m) USDA: 4 to 9.