The only maintenance Clematis require is pruning, but that can be a problem. When you buy a Clematis it's label it will state to which of the pruning groups it belongs either 1, 2, or 3 and this is a very necessary guide.
If you are planting a new Clematis you can use the table below which sets out when to prune each group of Clematis. There is an old gardening saying, which might help if you are not sure what type of Clematis you have, "If it flowers before June, don't prune."
If you inherit a garden which has in it established Clematis, and you have no idea to which group the plant belongs, the only way to work it out which group is to see to when it flowers. Broadly, but not an absolutely fail safe method, when a Clematis flowers is a rough guide as to how and when to prune it. If you have no idea what it is, and no other way to identify it, this is the best you can do.
Clematis which flower early in the year, March, April, or early May are mostly likely to be of the groups known as Alpina, Macropetala and Montana which for pruning purposes are "Group 1" Their flowers are produced on growth made the previous year, which means the plant must not be pruned early in the year in the spring, or you will cut off the buds and branches on which the flowers are formed, and it would not flower that year.
The next group of Clematis, very popular because they have large showy blooms and flower from Midsummer such as 'Nelly Moser', (Image above center) 'The President Niobe' and many other varieties are all known as "Group 2"
Finally, the late flowering Clematis are a bit confusing, some have large flowers such as 'Jackmanii', other scan be small viticella, so the flowers are different but distinguishable by the fact they all flower late in the season and are known as "Group 3"
If you can make a note of when the Clematis has flowered you can make a judgement on how to prune it : early spring flowering are usually group 1; summer flowering group 2 and later summer flowering group 3 although the only fail safe way is to fully identify the Clematis, and then to check to which pruning group to which it belongs. There are hundreds of types of clematis and new ones being bred all the time so its not easy; you can try this rule of thumb first. Now you know which Clematis or pruning group it is - what to do next ?