Most amaranth plants cannot amaranth survive winter in cold zones. They die at the first hard frost in fall. Only growers in warm zones 9 to 11 can keep plants going year round. In all other zones, you must treat them as one-season annuals.
The plant has very low winter hardiness for both grain and globe types. Tops die at any temperature below 32°F (0°C). Roots die too in cold soil. Frost wipes out plants in one night. There is no way to bring them back from a hard freeze.
I lost my first globe amaranth plants at the first frost of October. The leaves turned black, the stems went limp, and the whole bed died in 12 hours. Now I save seeds each fall and replant fresh seedlings each spring instead of trying to save the plants.
Frost protection can buy you a few extra weeks in fall. A sheet or row cover over the plants on cold nights helps. Drape it lightly so the fabric does not crush the blooms. Remove it each morning so the plants get full sun and air.
This trick works for light frosts down to about 28°F (-2°C). Anything colder will still kill the plants. The goal is to push the bloom season by two to three weeks, not to keep plants alive through winter. Set up the covers when frost is forecast for your area.
Your USDA zones rating tells you what to expect each winter. Zones 9, 10, and 11 stay frost-free most years. Globe amaranth can live as a short-term perennial there. Zones 1 through 8 will kill the plants each winter without fail. Plan for annual replanting in cold zones.
First frost dates by zone help you plan ahead. Zone 5 sees first frost in mid-October most years. Zone 7 gets first frost in early November. Zone 9 may not see frost until December if at all. Mark these dates on your calendar each fall.
If you live in zone 7 or 8, you can try to save plants by potting them up. Dig up the best plants before first frost hits your area. Place each in a 10-inch pot with fresh potting mix. Move the pots indoors to a sunny window for the winter months.
Keep your indoor plants near a south window with at least six hours of sun. Daytime temps should stay near 65°F (18°C) for the best results. Water lightly when the top inch of soil feels dry. Skip the fertilizer until spring to keep growth slow and tight.
Overwintering plants indoors is more work than starting fresh from seed each year. Spider mites, aphids, and dry indoor air all stress your plants. Many growers find it easier to just save seeds and start new plants in spring. You get healthier plants this way too.
Globe amaranth has very low cold tolerance at any life stage. Young seedlings die at 35°F (2°C) even without frost. This is why you must wait to plant outdoors until nights stay above 55°F (13°C) in spring. Rushing the planting date kills your starts fast.
To save seeds for next year, let some flower heads dry on the plant in fall. Cut them before the first hard frost. Bring them indoors and finish drying for two weeks in a paper bag. Rub the heads to release the seeds, then store them in a cool, dry spot until spring.
Seeds stay viable for one to two years in cool, dry storage. Toss in a packet of silica gel or some rice to soak up moisture. Label each bag with the variety name and date. Plant them indoors six weeks before your last frost date next spring.
In my experience, fresh saved seeds sprout better than store-bought packets some years. The germination rate stays near 80% for the first year of storage. Older seeds may drop to 50% or lower over time. Use fresh seeds for the best results each spring.
Skip any plans to leave plants in the ground over winter in cold zones. The roots cannot handle frozen soil. Even mulch will not save them in zones 7 and below. Pull the dead plants in late fall and compost the stems. Start fresh next spring for the best results.
Plan ahead so you do not lose your favorite varieties. Save seeds from your best plants before any frost hits. Buy backup seed packets from your local store too. With both options ready, you will have plenty of plants to grow next year with no stress at all.
Read the full article: Globe Amaranth: Grow, Dry, and Design
