Thanks for writing. I don't usually recommend growing plants in the ground underneath established pines or other evergreens. The reason for this is the evergreens have a massive root system that absorb's the lion's share of moisture and nutrients from the soil. The other main reason is that in many cases, the evergreens block out too much light for most shade-loving perennials to grow well.
That said, if there's enough light under your pine, you should be able to successfully grow plants in pots or large planters. Just about any houseplant should grow well for the summer, as well as annuals including impatiens, browallia, torenia, and sweet potato vine.
Senior Garden Editor, BHG.com