Daisy-like asters (Aster spp.) feature bright yellow central disks surrounded by rays of brightly colored petals. Flower color differs among the different types, but white, pink, purple and blue are common. Asters thrive as perennials in U.S. Department of Agriculture hardiness zones 9 and below or as annuals outside their preferred climates, although hardiness can differ between the various cultivars. The flowers grow readily from seed, often flowering by summer's end. Start aster seeds indoors or outside in a cold frame about six weeks before the last expected frost. Plant them outside in late spring or early summer.
First, choose an appropriate planting site. Asters will do best in full sun, but many varieties can also grow in partial shade. Well-drained soil is best.
Prepare the planting site, especially if it’s a new garden bed, by mixing in compost, composted manure, or another source of organic matter and nutrients.
If you’ll be planting outdoors, follow the seed spacing instructions for your variety. Many asters can be spaced 3 inches (8 cm.) apart, then thinned to 12 inches (30 cm.) apart after they emerge.
Whether planting indoors or outdoors, cover the seeds with 1/8 inch (0.3 cm.) of fine soil. Aster seed sowing by scattering the seeds in a wildflower planting is also perfectly fine. Water the seeds after planting, then keep them evenly moist until seedlings emerge. This can happen between 7 and 21 days after sowing, depending on the aster variety.