Be careful what you wish for. We moved to a new/older home and comfrey was growing rampantly everywhere. I recognized it immediately, as my in-laws planted it as a for-profit crop, and lived to rue the day! It grows very well in western Oregon and spreads rapidly. So beware, Be ee ee ee ware! (hummm along)
Thanks for the warning, Other readers also report comfrey's agressive nature. Some cultivars, and the Russian variety, are supposed to be less or non self sowing, but take that with a grain of salt. The deep roots of Comfrey make it a very durable plant.