Catherinet,
I do not think it's luck - even in your zone! Once planted, our garlic chives spread like wildfire and are hard to get rid of here. I like them in our culinary herb garden, but far fewerr would sure save me some time! They multiply in clusters by root and seed freely from their pretty white flowers that are so long lasting and delightful.
Good luck, and glad YOURS were at least containerized :o

THanks gladofit!

30 years ago I was given a pot of garlic chives as a house warming present and told by the giver that if I wanted more, they had it 'all over their garden.' I mentally put it down as a weed and tossed it out. It came up the following year (without even being planted) and survived nicely on its own and I finally decided that it was a good, reliable perennial with an attractive flower and moved some into the flower garden where it has been ever since. Cutting back the flowers before they set seed will prevent it from spreading where it isn't wanted.