You have to grow celosias as annuals if you live in U.S. Department of Agriculture plant hardiness zones 2 through 9, but if you live in USDA 10 or 11, you can grow them as perennials. If you grow them as annuals and want early blossoms, plant the seeds indoors six to eight weeks before the last expected frost in your area. Transplant seedlings you grew from seed or purchased from a nursery after the last expected frost.
Seeds or nursery starts of Celosia argentea are either plumed or crested. Plumed cultivars bear fluffy, feathery heads containing hundreds of tiny flowers. Crested cultivars have brilliant flowers that suggest a rooster’s comb, hence their common name, cockscomb. Plumed Celosias that have been named All-American selections include “Fresh Look Red” (Celosia argentea “Fresh Look Red”) and “Fresh Look Yellow” (Celosia argentea “Fresh Look Yellow”), both of which produce blooms all summer without deadheading, plus “Apricot Brandy” (Celosia argentea “Apricot Brandy”) that yields apricot-orange plumes and “New Look” (Celosia argentea “New Look”) that has dark bronze foliage. Crested or cockscomb cultivars include “Big Chief Mix” (Celosia cristata “Chief Mix”) that yields gold, red, rose or yellow flowers that resemble cauliflower or coral and “Jewel Box Mix” (Celosia cristata “Jewel Box Mix”) an 8-inch-tall flower with bronze leaves and fan-shaped flower heads colored bright gold, pink, red, salmon or yellow.
Cultivars of Celosia spicata grow narrow spikes of flowers that resemble heads of wheat, hence they are sometimes called wheat celosias. They have cylindrical rose or pink flower heads with silvery-white at the bottoms of the flowers, giving them a metallic sheen. They are more shrubby than argentea cultivars, and their flowers are more muted in color. Examples include “Flamingo” (Celosia spicata “Flamingo”) that yields pink or purples that fade to white or silver and “Pink Candle” (Celosia spicata “Pink Candle”) that grows deep pink flowers highlighted with silver.
Celosias will take about three months to flower after you plant the seeds. They do not like soil that is less than 60 degrees Fahrenheit. If you start them indoors to transplant as annuals, plant the seeds 1/4 inch deep in moistened seed-starting mix, then cover the pots in plastic wrap. Keep them in temperatures from 70 to 80 degrees until they germinate, which should take 10 to 15 days. After they germinate, put them under fluorescent lights or move them to a sunny, south-facing window. They will first grow cotyledon or embryonic leaves. When they grow two leaves that look like leaves on an adult plant, remove the weakest seedlings.