I've been mapping and identifying plants around a very old yard that's been not planted or bothered with for maybe 25 years (other than mowing). Yesterday I noticed stocks blooming next to the house. Now, I've always thought of stocks as annuals, and I know they can reseed. However this looked like a perennial that had been mowed and had branched out under ground. Are some types of stocks perennial in zone 5? Are they common in old neglected gardens? Thanks, Leah