Globe amaranth perennial or annual behavior depends on where you live. The plant is a tropical annual in most of the U.S. but a true perennial in frost-free spots. In zones 9 to 11, it can live for years if winters stay mild.
I have grown Gomphrena globosa in three different zones over the years. In a zone 9 yard in Florida, my plants came back for three full years in a row. In zone 5 Wisconsin, the same plants died at the first hard frost in October.
The plant comes from warm parts of Central America and Brazil. It evolved with no need to survive cold winters. That makes it a tender perennial that cannot handle frost. Any night below 32°F (0°C) kills the tops fast.
Your local USDA hardiness zones tell you what to expect. In zones 9, 10, and 11, plants act as short-lived perennials. They may live for two to four years before they decline. In zones 8 and below, treat them as one-season annuals.
UF/IFAS Extension gives clear planting dates for each zone. Zone 7 growers plant from June to August for a short window. Zone 8 stretches from May to September with a longer season. Zone 9 gardeners can plant from April through September for the biggest harvest.
Plants reach 18 to 24 inches tall in one season. They bloom from 6 to 14 weeks after planting, then keep going until frost. In tropical zones, plants pause in cool spells and pick up again when temps warm back up to 65°F (18°C) at night.
In zone 9 winters, I have seen Gomphrena globosa survive light frosts with row cover. A sheet thrown over the plants on cold nights kept them alive. They came back with full bloom the next spring with no extra care from me.
If you live in zones 7 or 8, you can pot up plants in fall. Bring them indoors before the first frost hits your area. Place them in a sunny window with daytime temps near 65°F (18°C). Water lightly through winter to keep them alive until spring.
Most growers in cold zones skip the pot-up method. Saving seeds works better and takes less time. Let some flowers dry on the plant in late fall. Pick the brown heads, rub out the seeds, and store them in a paper bag for spring.
Gomphrena globosa seeds stay viable for one to two years when stored cool and dry. Toss a packet in a jar with rice or silica gel to keep moisture out. You can replant the same line for many seasons this way.
Plants also self-seed in zones 7 and warmer if you leave heads on through fall. Skip the cleanup in your beds and watch for tiny seedlings in late spring. New plants sprout when soil hits 65°F (18°C) and grow fast in warm weather.
For zones 5 and 6, accept that this is a one-year flower for you. Plan to buy or start new seeds each spring. The good news is one packet costs less than five dollars and gives you dozens of plants with very little work.
These are not classed as winter hardy plants like coneflowers or Black-eyed Susans. Do not expect them to live through snow or hard freezes outdoors. But they bloom so much in one season that the annual cost is worth every penny in most yards.
Pick varieties that match your goal. Buddy and Gnome types work well for small pots you bring indoors. QIS and Strawberry Fields suit big outdoor beds where you grow them as annuals. Either way, you get months of bright color from a simple pack of seeds.
Read the full article: Globe Amaranth: Grow, Dry, and Design
