Give bulbs sunshine, good soil and water and they'll reward you by returning year after year. The problem is that bulbs only bloom for a short while during the season and then go dormant. It's easy to forget where you planted what bulbs. It is possible to narrow down what types of flower bulbs have been planted by their foliage.
Determine when the foliage appears. Spring bulbs grow leaves in early to late spring, summer bulbs in early to late summer. If the leaves appear in early spring, common flower bulbs would include snow drops and crocus. Mid-spring flowers include tulips, daffodils and hyacinths. Late spring flowers include iris. Summer-blooming flower's foliage includes amaryllis, gladiolus and lilies.
Measure the length of the foliage. Bulbs with leaves less than 6 inches include crocus, snow drops and grape hyacinths. Bulbs with leaves between 6 and 12 inches long include tulips, daffodils, hyacinths and lilies. Leaves over 12 inches long include iris, alliums, amaryllis and gladiolus.
Look at how the leaves grow. Some grow from a central stem, like gladiolus, iris and lilies. Others grow in a cluster, like alliums and daffodils. Hyacinths and tulip leaves grow around the central flower bud.
Determine the shape of the leaves. Most bulbs have narrow leaves but there is a lot of variation. Amaryllis leaves are long, about 1/8-inch thick and straplike, growing to 24 inches long. They bend in a graceful arch. Gladiolus leaves are thin, pointed at the end and stiff. Tulip leaves curve inward around the flower stem. Hyacinth leaves are thicker than tulip leaves and are rounded on the ends.