Answer: Annuals are plants that grow, flower, set seeds and then die. There are cool season annuals and warm season annuals. Each will need to be replaced at the end of their growing season. Perennials are plants that live for more than 3 years. There are both woody and herbacious perennials. Woody perennials are plants that lose their leaves in the fall but their woody stems are persistent throughout the winter and they will leaf out each spring; herbacious perennials are those that die down to ground level with the first frost but in the spring the roots produce new growth.
Sunny windowboxes can overheat in the summertime so you will want to plant annuals or perennials that thrive in sun and dry soils. Portulaca is one to consider, Threadleaf Coreopsis, salvia and catmint are other suggestions. Another classic hot, dry, sun loving perennial is the Catmint.
Best wishes with your garden!
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