Posted: 21/03/2013 at 14:17
Are these unplanted bulbs or bulbs in pots cos if you're in the northern hemisphere they should have been planted out in the ground from September to November or in pots and then kept cool and dark until the first shoots showed.
Frits, bluebells and snowdrops in particular don't like drying out and may not work now but, assuming they're viable, they will slowly spread by offsets and self seeding. How quickly they do it depends on how happy they are and it' seasy enough to divide up any clumps that become congested in a few years time if you do it in teh green once the flowers have faded.
The only one I would have thought coul dget invasive is the lesser celandine.