Planting under pine trees is a real challenge. You not only have to contend with the shade, which sharply limits what you can grow, but also the constant shower of pine needles, which have a high acid content. But that doesn't mean you need to keep nothing more than a mound of dirt underneath your pine trees. Several plants can function quite well there, and with the proper preparation, you just might find yourself with a lovely pine tree garden.
Find plants that can stand the shade and acidity of living under a pine tree. Azaleas and rhododendrons are known to thrive in both shade and acidic soil, while hydrangeas, which are typically pink in most gardens, sport bright blue flowers when planted in acidic soil. They also like the shade, which makes them ideal candidates.
Dig a hole twice as big and twice as wide as the root ball of the plant you're going to put under the pine tree. Fill the bottom half of the hole with good topsoil. Pine trees sap a lot of nutrients out of the ground, so it's up to you to put them back in. A good place to start is by adding topsoil with lots of organic matter to the existing dirt.
Place your new plant on the topsoil and center it in the hole. Fill in the rest of the hole with topsoil. Spread pine needles around the plant, using it as mulch to retain water. Water thoroughly.