I recently planted one of those "flower carpets" and ended up with very tall sunflower plants. I love them, but don't know anything about growing them. Do I cut the plants back at some point, will they come back into bloom every year, etc?
Hardiness Zone: 11
BARBARA from LONG BEACH, CA
Sunflowers are annuals (meaning they complete their lifecycle in a year), and will not come back every year on their own, but you can easily save their seeds for planting next season. Don't cut them back, just let them grow. Here are some tips from growing sunflowers.
Like their namesake, sunflowers appreciate lots of sun-the more the better. Seeds should be planted approximately 1/2 inch deep and 6 inches apart (or according to specific package directions) in fertile, well-drained soil as soon as danger of frost has passed. Leave 3 feet between each row.
You can also grow them in containers, but make sure you use a large enough pot to accommodate their large roots (at least 15-20 inches deep for mammoth varieties).
The seeds germinate very quickly (from days to a week or two) and take anywhere from 75-90 days to reach maturity.
Thin seedlings to 12-18 inches apart when they reach 3 inches tall (container plants can remain somewhat closer together).
Sunflowers need plenty of water, but stress from too much or too little water can damage developing seed heads. Try to keep the soil around them evenly moist but not wet.
They are also voracious feeders and appreciate regular applications of fertilizer. Try a half strength organic liquid fertilizer every two weeks and make sure to replenish the soil with plenty of compost at the end of each growing season.
As the plants grow, the petals will start to drop and bees will pollinate the florets on the heads. The heads usually start to "bow down" a bit at this point. When the florets on the heads dry up, the seeds behind them will start to plump up and harden. At this point you can leave the heads on the stalks to dry, or cut them off and hang them upside down to dry indoors. If you leave the flower heads to dry on the stalks, be sure to cover at least some of them or you'll lose the seeds to the birds.
When the seeds are fully dry, scrape them off the heads using your hand or a small wire screen. Store in an airtight container until next season, roast them for eating or save them for the birds.
Some of the giant varieties may get top heavy and flop over in windy or wet weather. Staking them will help prevent this.
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By Linda (Guest Post) 07/28/2006
After they bloom the flowers will go to seed and drop their seeds and should come back next year.