Any perennials can be planted in window boxes and pots. The problem is that they won’t survive winter unless the planter boxes or pots are sunk into the ground in fall. Otherwise the pot or box will repeatedly freeze and thaw and refreeze and rethaw. All this thawing and refreezing will kill perennials or hardy shrubs and trees planted in containers. Once they go dormant in the fall and the ground freezes, they need to stay frozen in a state of dormancy until spring. Besides, perennials only flower for a couple of weeks so aren’t the best option for containers. Annuals flower continuously all summer long making them a much better choice for window boxes and planters.