Fall-planted flower bulbs are sometimes called hardy bulbs because, in many areas, they can stay in the ground over winter. Many fall-planted bulbs, such as daffodils, crocus and tulips, bloom in the spring. Others, like Dutch iris and lilies, bloom in late spring to summer. Most bulbs grow best when they are planted in well-drained soil. For the most dramatic impact, plant flower bulbs in groups. When considering what flower bulbs to buy online, take into account your garden space and the mature height and spread of the plants. Other factors to consider include hardiness zone, sunlight requirements (full sun, partial shade, full shade), bloom times and flower color.