If you're looking to get year-round color in your garden, then here is a list of flowers you should plant. They will help ensure that you don't have any bland spots during the season. The list below will highlight one flower that blooms during each of the 4 seasons.
Peonies For Spring Color
Peony plants are beautiful flowers that bloom in the spring. They come in a variety of colors: pink, white, red, and yellow. They are perennials, so you don't have to worry about digging up your garden and re-planting new flowers every season. You should plant them in very well drained soil, and they also need full sun. They do OK in harsh winters, so it's not an issue if you live in a cold climate. They are fine for gardens in Zone 3 through 8. Besides their beautiful flower, they also have a nice green leafy body that will stick around during the summer and into the fall (when they turn purplish or red.) So, these make a great flower for walkways, edgeways, property lines, or anywhere you want a nice row of low green for many months, and a burst of color in the spring.
Dahlia For Summer Color
Dahlia's are a stunning flower. They have large, brightly colored petals that can be red and pink. They are best suited to warmer climates (zone 7-11). They were originally a Mexican flower, but are planted farther north nowadays. They will be planted in tuber form. If you're unfamiliar with tubers, they are similar to tulip bulbs. You plant them in the ground like a giant seed and in the summer the dahlia will bloom.
Aster For Fall Color
The Snow Flurry variety of the Aster plant is a beautiful flower for fall color. It is a low, shrub like flower that blooms tiny white petals. The flowers attract butterflies, which is always a nice thing to have in your garden. They grow only to about half a foot, which makes them great for areas where you want a low profile, and they do well in zones 3 through 9. They should have full sun, and do well in a variety of soils. They are very low maintenance flowers.
Snowdrop For Winter Color
Winter is often the trickiest time to get nice color into your garden. Well, one great choice of flower is the snowdrop. They are sold as bulbs, and they bloom in the winter. Unlike many flowers, snowdrops actually prefer the cold, so if you're in a really hot and humid climate, these flowers are not going to do well. It's best to plant them in zones 3 through 8. They are not a thick "shrub like" flower, but instead resemble more crocus or small tulips. They have a single stem and a single, beautiful white flower that bends over like at the top. It would be a good idea to plant several snowdrop bulbs around each other to create a dramatic arrangement of the group standing together.