Hello, I underplanted an established hydrangea with snowdrops in autumn and they have come up and are out now, however maybe due to the difficulties of planting them when the hydrangea was in full force, or maybe due to stinginess or perhaps some havent made it, it is very very sparse.
Should I get loads in the green to fill the gaps or will they naturalise and reproduce like billy-o?
Since you planted them in the autumn I am guessing you planted individual dry bulbs. If so, leave well alone and they will soon bulk up into natural looking clumps, and set seed (if they are not double)
I get a very high failure rate on dry snowdrop bulbs - they are a bit notorious. If you are desperate for clumps fast, get some in the green, otherwise they will start to bulk up by themselves as trethew says, but this can take some time.