Fall bulbs, also known as spring flowering bulbs, are hardy bulbs that are planted in the fall and bloom in the spring or early summer. Examples include tulips, daffodils and crocuses. There are many types of plants that are considered to have bulbous root stems--including rhizomes, tubers and corms--even though they are not true bulbs. As long as they are winter hardy in USDA hardiness Zones 5 to 7 (as most fall bulbs are), Pennsylvania is the perfect place to plant them in the fall before the first freeze.
Prepare a place to grow your fall bulbs. It should be in full sun and have rich, well draining soil. Turn over the top 12 inches of your soil and mix in organic matter, such as 3 to 4 inches of peat moss or compost.
Dig holes to a depth that are 2 to 3 times as wide as the bulbs. This is a general rule that applies to true bulbs and corms. However, if your fall bulbs are actually tubers or rhizomes, they are planted closer to the surface; the planting depth varies from plant to plant. See http://wilsonbrosonline.com/How-To/Planting-Instructions/How-To-Plant-Flower-Bulbs.aspx for the planting depths of common bulbs.
Space the bulbs according to their individual needs. There is no guideline for spacing bulbs since bulbs grow to be different mature sizes. For instance crocuses need to be spaced only about 3 inches from one another, while lilies need more like 10 to 12 inches of space in between plants.
Backfill the soil and pack it down with your hands lightly. Water the area well and mulch. Use between 2 to 5 inches of mulch, such as straw or bark. In Zone 5 you will need more mulch than in Zones 6 and 7.