Answer: Garden centers generally receive their plants about 2 weeks after the last frost date of the season. This is so gardeners can safely plant them in the garden and not have to worry about freezing temperatures killing their new plants. Your last frost date in zone 5 can be anytime between April 15 and 30. So, you can expect to see summer annuals and perennials in your garden center about the end of April or the first of May. The plants you saw on your last visit are considered cold-tolerant plants and therefore are stocked during late winter and early spring.
Hope this clarifies things for you.
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