Centaurea Montana is quite an easy plant to grow and spread, In fact it can be a bit of a thug if it is not controlled properly and can quite easily spread very quickly. This said however it has stunning cornflower like blooms and will grow pretty much anywhere. Easy to grow from seed and also easy to split. Once it has finished flowering cut it to the base and it should flower again later in the season. At the end of the season again cut it back to the ground and it will happily over winter. If the plant has spread to much then just pull it out. Montana is very hardy so it will not hurt the plant. The roots are quite deep so bear this in mind when removing unwanted spread.
Below the foliage is clearly visible and obvious due to the hairs that are on the leaves. As the flower spikes are produced they will need staking as they will become top heavy and fall over. Also be aware of Aphids as they sometimes like to take up residence in the plants.