Crocosmias: are they invasive?

The Crocosmia most people will be familiar with is the plant commonly called Montbretia, lovely hanging orange flowers in late summer, but invasive or at least, difficult to get rid of. Actually The desirable varieties of Crocosmia are mainly bred from different species than those crossed to create Montbretia. The first two species introduced to Europe were C. aurea and C. pottsii, these two were crossed in the 19th century in Nantes, the result was Montbretia, now these two original plants just happened to increase using thread like roots that sprout from the corm (bulb) and each root (stolon) could make a new corm at the end, this feature was exaggerated in Montbretia so that when a clump of corms is dug up many brittle stolons break off, each one capable of carrying on growing into more corms.

Do not fear! Modern plants come (mainly) from two other species, C. paniculata and C. masoniorum, a beautiful and elegant plant that is not common in its native South Africa. Other species are used too and a few hybrids do still produce stolons, but not on an invasive scale. Usually the corms grow in ‘chains’ a new corm each year grows directly on top of the old one (simplified but you get the idea) so they don’t take over, indeed some increase slowly and never move from their allotted space.