Posted: 26/09/2015 at 10:05
Clematis require rich soils so you'll have to improve yours with loads of well rotted garden compost and manure to provide all the nutrients they need and improve water retention. There are many varieties to choose form but none that flower most of the year.
There are some evergreen ones that flower in early spring. The deciduous ones come in many shapes and forms of flowers but you should look at the Group 2s which flower in May and June and then, if fed and pruned well, again in late summer. The group 3s, which are easiest to prune as they just get cut back hard in spring, can flower from June through to September if well fed.
Have a look at this site which lets you select plants according to group, flower colour and aspect - http://www.clematis.hull.ac.uk/new-clemlistsearch.cfm You can then seek out the varieties you like at your local nursery or garden centre or from nurseries that do mail order such as Taylor's or Thorncroft or Raymond Evison