sunflower seeds for planting - to plant mammoth sunflower seeds - packet of about 100 flower seeds! raw earth colors plant. grow. love. about 12 grams of sunflower seeds for planting with an 85% germination rate. product of usa. sunflowers grow best in locations with full sun. they are remarkably tough and will grow in any kind of soil as long as it is not waterlogged. they do fine in soils that are slightly acidic to somewhat alkaline (ph 6.0 to 7.5). once sunflowers get started, they can tolerate drought as befits plants whose ancestors grew happily in dry prairie regions. although sunflowers can be started indoors in individual peat pots, it is easiest to sow seeds directly into the soil after all danger of spring frost is past. however, where the growing season is short, sunflowers can be safely planted up to 2 weeks before the last expected spring frost. sunflowers can take a chill or two. where growing seasons are long, it is best to wait until the soil temperature reaches 55 degrees to 60 degrees f. to plant sunflowers: space seeds about 6 inches apart in a shallow trench between 1 and 2 inches deep. in sandy soil, 2 inches deep is better. cover and keep watered until seeds sprout in 7 to 10 days. when first true leaves appear (the second set of leaves); thin plants to about 2 feet apart. depending on the variety, sunflowers will mature and develop seeds in 80 to 120 days. sow a new row every 2 to 3 weeks to enjoy continuous blooms until the first frost.