There are three members of the genus Picea (spruce) and family Pinaceae native to Pennsylvania: Picea glauca (White spruce), Picea mariana (Black spruce), and Picea pungens (Blue spruce). We are not sure which one you have but you can follow the plant links above to our webpage on each to find out what their prospective heights and best environment are. Of these, we chose Picea pungens (Blue spruce) for our example. We need to know what kind of soil and sunlight they require in order to understand what might grow beneath them. The spruces apparently need medium amounts of water, part shade, and moist, rich, acidic soil.
In selecting groundcovers, you have several problems. That deep shade and the extensve underground root system of the spruce is not going to encourage much in the way of growth beneath it. We found an article from the Edmonton Journal on that exact subject, Acidic Soil Beneath Spruce Trees. Of course, the author included several plants not native to North America, so we will find some that are native. We went to our Native Plant Database to begin our search. Using the Combination Search, we first chose Pennsylvania for the State, grass or grass-like for the Habit, part shade or shade for Light Requirement, moist for Soil Moisture and 1-3 ft. for the mature height. We ran the same search with herb (herbaceous blooming plant) and fern for the Habit. There is no opportunity for selecting the preferred soil acidity in our Database, but you are going to have an acidic soil with all those needles falling on the ground over a 30-year time period. By following each plant link to our webpage, you can find out more about the Growing Conditions of that specific plant. We restricted our suggestions to those needing a moist acidic soil.
Grass or Grass-like:
Herb (Herbaceous blooming plant)
You may have difficulty locating these plants in large commercial nurseries. Go to our National Suppliers Directory, put your town and state or just your zip code in the "Enter Search Location" box and you will get a list of native plant nurseries, seed suppliers and consultants in your general area. All have contact information so you can get information on availability and location before you leave home.