I grow many of my herbs in pots because I like to move them around the garden. When they are looking at their best they are given a prominent position, but before and after that they live somewhere else. It is important to take good care of potted herbs - well, any potted plants really - because they rely on human intervention to provide the right levels of water, nutrition and growing-space, something they can more easily correct of their own accord if they are grown in open soil. Chives produce a very vigorous root system and they can easily become pot-bound, like this:
When they get like that they cannot get enough moisture or nutrition, so it is advisable to re-pot them to restore their vigour. I tip the plants out of their pots and trim away about 75% of the root-ball, using an old kitchen knife, before putting them back into their pots, filled with fresh compost, into which they will soon spread out.
For the past couple of years I have covered the compost in my Chive pots with pea-shingle, in the hope of suppressing the growth of moss, but it hasn't really worked, so I'm not going to bother with it this time.
So that's it - the Chives have been re-planted with ust the tips of their first shoots of the year just sticking up above the compost, and ready for the off. Before long I will have to do very much the same sort of thing with my potted Mint as well.