Even easier, and maybe more inpactfull, is to bury small clay pots upside down in your garden with the little hole in the bottom (now top, since the pot is upside down) exposed. If you are lucky bumblebees will move in. There are even colony building bumblebees where I live. Bumblebees are superior polinators as they are more resilient to cold and rain. Where I live the (italian) honeybees stay inside the hive if there is even a chance of rain, while the bumblebees will go out in any weather.