[AlaninCarlisle]

For as long as I can remember (35 years) we've had a clematis on each side of the front door. They seem to be similar types, quite vigorous and with large blue flowers in late spring, ie now. One of them grows quite gangly and seems to expire as soon as it comes into bloom (but comes back the following year). The other one stays reasonably compact, looks healthy and is a mass of flowers. Both are growing in ancient soil in beds excavated many years ago in the tarmac.
What treatment should I give the sickly one and when, please? The options seem to be to dig them both out and replace the soil and discard the sickly one or just replace the soil and persevere with the sickly one or maybe just give them both an intensive organic feed.

[grinling]

I have RHS Practicals on Clematis. it says plant away from a wall and plant 10-20 deep including the stems to increase roots (same applies for tomatoes). mulch well and water into a pot buried next to the plant.
feed with liquid seaweed or tomato feed. before mid summer take cuttings.

I need to read this book, rather than hack my clematis when it goes everywhere 

[mrs bouquet]

That is very sound advice from Grinling.   As yours has been planted a while ago, you could maybe try to put the watering pot in the ground fairly close by, but be careful of its roots.  Also, if you decide to try to "build it up", do not use anything that is too strong.  I did that once with manure and the acid burnt it out.  Good luck, Mrs Bouquet