Flower bulbs are some of the easiest and most rewarding plants to grow. Some flower bulbs, such as tulips, daffodils and crocus, are planted in the fall and bloom the following spring. Other flower bulbs, such as dahlias and calla lilies, are planted in the spring and usually bloom in the summer. All flower bulbs grow best in well-drained soil. Gardeners who grow flower bulbs often amend their soil with compost to improve the soil structure and drainage. When buying flower bulbs, make sure they are suitable for your grow zone. Other factors to consider are their mature height, bloom time, flower color and form.