Thank you for your question.

First of all, don't assume the soil is too acidic because a pine grew there. Pine needles generally do not lower mineral-soil pH enough to be a major concern. However, you should remove any thick mat of undecomposed needles. It will also be important and necessary to have a soil test conducted on samples from the garden. This will provide information as to what types of soil amendments, and in what amounts, should be added to the soil. See:

https://soiltest.cfans.umn.edu/testing-services/lawn-garden

As to the types of plants to put in this garden, I would recommend such things as:

Butterfly milkweed (Asclepias tuberosa)

Common milkweed (Asclepias syriaca)

Prairie blazing star (Liatris pycnostachya)

Rough blazing star (Liatris aspera)

Wild bergamot (Monarda fistulosa)

Purple prairie clover (Dalea purpurea)

Smooth blue aster (Symphyotrichum laeve)

Ohio spiderwort (Tradescantia ohiensis)

Also see the following for additional possibilities:

https://extension.umn.edu/yard-and-garden-news/native-plants-minnesota-gardens

https://www.dnr.state.mn.us/prairie/native/types-prairies.html

Good luck. You are embarking upon a great gardening adventure. Please get back to us if you have any additional, related questions. Thanks for using our forum