Planting times vary according to the types of plants involved and the local climate conditions. Traditionally, fall and spring are thought of as good planting times. Seeds do not germinate in cold weather and many plants go dormant during the winter months. In mild climates, flowers and vegetables are grown year-round and planted every few months. In each season, garden centers display the best plants to grow at that time in your the area.
Plant annual flowers in the spring for summer blooming. Annuals are planted, grow, bloom and die in one season. Many of summer's most popular flowers are annuals such as zinnias, marguerite daisies, asters, cornflower, and marigolds. Young annual plants are available at the garden center each spring in six-pack plastic trays. Annuals can also be grown from seeds planted in February to April in most areas. In warm climates annuals can be planted all year long.
Fall and spring are both good times for planting perennial flowers such as delphinium, daisy, coreopsis, and daylilies. Plant purchased perennials in the fall one month before the first frost. In spring wait until all danger of frost is past before you set perennials in the ground. Check your local garden center for frost dates or consult the U.S. Department of Agriculture Plant Hardiness Zone Map.
Seed packets are the best guide for planting times of individual vegetables. The general rule is that seeds will not germinate in temperature below 50 degrees F. Vegetables do not like cold, wet soil. Wait to plant seeds until spring frost periods are over and the soil warms. The earliest vegetables to go in the ground are peas, lettuces, spinach, and collards. They are called "cool-season" vegetables. Tomatoes are best planted in April or later depending on your climate.
Fall and spring are the best time to plant shrubs such as lilac, azalea, and barberry. When planted in fall, they have a chance to establish their roots before the first frost and dormant phase of winter. Roots continue to gain strength during winter even when the plant shows little sign of top growth. Plant shrubs in springtime also, when increased daylight and sunshine encourages strong growth.
Roses are sold "bare root" during the winter months to be planted in early spring. They are in a dormant stage with no green growth. Roses sold in 5-gallon containers are usually growing and blooming and can be treated as shrubs. Plant them in spring when the soil warms or fall before the first frost date.