Clematis pruning

Pls advise - there are 2 clematis which climb up and over a wall which edges my upper patio. One has white flowers the other pink, and they have almost finished flowering. There are masses of new shoots all over the plants, which are well over 12 years old and don't think have ever beern pruned. We moved into this house a couple of years ago and now are ready to give serious time to the garden - especially the upper patio which is by the kitchen. In the autumn and winter when the clematis leaves have gone, all we are left with are a VERY woody mass which looks like a pile of straw. We would like to keep the plants going, but they obviously need a good prune but when? We are a bit reluctant to hack off the new shoots, but want to get to the underneath somehow. Any advice would be helpful as we are not experienced gardeners. Thank you

Are they large flowers?  If so, they are probably Group 2 (early large flowered) and will produce a 2nd set of flowers later in the year.  What you should do now is remove all of the seedheads by snipping them off just above a pair of leaves.  The new shoots you are seeing will produce the 2nd crop of flowers and you can try and train this downwards to cover some of the bare areas.  That same growth will produce the early flowers next year.

You only do the main pruning in early spring.  If severe pruning is needed, you can cut them back to the lowest pair of buds on each main stem.  Doing that will mean you will lose the early flowers for that year, but they will still produce flowers later in the year.  If you do cut them back hard in spring (even to the ground if you can't find any buds on the lower parts of the stems), they will usually produce new shoots from below ground, effectively revitalising them.  If you do that, give them a good feed and mulch with a few inches of compost to build the soil level up at the roots.

To be sure of what variety and group they are, is there any chance you could upload some photos? Other clematis groups might need a slightly different approach.

To quote what Monty Don said about Clematis " If it flowers before June no need to prune" but found this anyway.

http://gardening.about.com/od/perennials/a/PruningClematis.htm

That's not quite right.  If it produces small flowers in early to mid spring it's a group 1 and only needs pruning to keep it in bounds by trimmming off excess growth after flowering finishes or to renew vigour from the base by cutting one or two stems at teh base and then leaving them to wilt.  They can be pulled out a couple of weeks later without doing too myuch damage to the rest.

Group 2s are the early, large flowered hybrids which flower on old wood in May and June.  These need to be dead headed once flowering finishes and can also be pruned to keep within bounds or renew vigour as above.  Both types should be fed as soon as they've been pruned and also in Feb/March when new growth appears.  Group 2s often go on to produce a second flush of flowers in late summer and do this best if given the earlier prune and feed.

Group 3s flower in summer on new wood and should be pruned back either to the gorund or to the lowest pairs of buds in Feb/March depending on how cold you are.  I sometimes have to leave mine till early April.  again they should be fed once new growth shows.  Group 3s can be large or small flowered.

The best way to check is to look at this site - http://www.clematis.hull.ac.uk/ - which allows you to search for info based on the clematis name, its description or a picture.

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