Sunflowers are annual flowers best started from spring through summer. Directly sow seeds outdoors or start earlier in cells in a greenhouse and transplant after last frost. Insure that seeds stay consistently moist throughout their germination period. Sunflowers are heavy nutrient feeders so amend soil appropriately. Be prepared to trellis plants as they have a tendency toward lodging (tipping over). Harvest whole heads and dry for sunflowers seeds if you can get to them before the birds.