There are three things you must look for when choosing flowers that will grow in pine needles. The first is to choose a flower that thrives on acidic soil, since pine needles are highly acidic. The second, assuming your flowers will be growing under a pine tree, is a flower that does well in the shade. And lastly, you need a flower that can grow well under drought conditions. The reason for this is that pine roots soak up virtually all water and create a droughtlike environment. Fortunately there are several different flowers that meet all of these criteria.
Consult with your local nursery regarding flowers that grow well in acidic conditions, such as those created by pine needles.
Ask your nursery expert about flowers that also grow well in shade and flowers that can withstand drought conditions, such as those brought about by pine tree roots.
Carefully loosen the soil where you wish to plant your flowers, being careful not to damage too many of the shallow roots of the pine tree. Add some organic manure to the soil and mix well until you have approximately a 50/50 mix of soil (with pine needles) and manure.
Sprinkle a small amount of lime onto the soil to reduce the acid content of the soil. If you have chosen flowers that do well in acidic soils, then you do not need much lime--no more than 1 lb. per 100 square feet.
Plant your acid-loving, shade-tolerant and drought-resistant flowers in your pine needle, manure and lime soil and water well.
Continue watering well every 2 to 3 days, keeping the soil damp but not soggy, until your flowers are well established.