It can become a pernicious weed if left to its own devices. There are 'tame' varieties, a small rock garden on which is well behaved, and a taller one whoch stays in a small clump. The most invasive is an old one which was called 'rose of sharon', and it really is a pain to get rid of once established. We moved here 16 years ago, and the garden was full of this hyoericum and red hot pokers. The pokers went in one removal day, but they hypericum is still trying to re-establish itself - and often nearly succeeds if I am away or cannot get outside for a week or two! It can look great in huge swathes in very large places or public gardens, but has o place in modern small spaces.