How To Grow Sunflowers From Seeds Outdoors. To begin growing your sunflower, fill a pot with compost to 1cm below the rim. To plant sunflower seeds in peat pots or paper cups, put two seeds per pot and just cover them with soil.
Keep under grow lights, sunny windowsill, or greenhouse. Fill a 16 by 18 inch (40 by 45 cm) pot with topsoil that has a ph between 6 and 7. Push the seed 1.5cm into the compost and water in.
If you’re saving the seeds to plant, store them in an airtight container in a cool, dry place until planting.
They can be started off indoors in early spring and will grow quite happily on a window sill for a time. Sunflower seedlings can take a bit of frost, and it’s safe to plant them outdoors about 2 weeks before the last expected frost date. Cover and keep watered until seeds sprout in 7 to 10 days. To plant sunflower seeds in peat pots or paper cups, put two seeds per pot and just cover them with soil.