Sunflowers will grow in just about any well-drained soil, and they are drought tolerant. Annual flowers that can grow to incredible heights in just one season. Continue reading below for tips on how to grow sunflowers from seed.
Season & Zone
Exposure: Full sun
Direct sow repeatedly after the last frost date. Starting indoors is possible, but does not gain much time. If sunflowers are allowed to get root-bound, they will lack stability at transplant time, and will require staking. Optimal soil temperature for germination: 21-30°C (70-85°F). Seeds should sprout in 10-14 days.
Sow seeds 5mm-1cm (¼-½”) deep. Space dwarf varieties 15cm (6″) apart, but give the giants lots of room at 1m (3′) between plants.
To grow really big plants with really big flowers, enrich the soil with organic matter and incorporate 2 cups of balanced organic fertilizer per 3m (10′) of row, and irrigate regularly. When the plants are 30cm (12) tall, dissolve 5ml (1 tsp) of borax (for boron) in 350 ml (12 fl oz) of water and spread the solution over 5m (15′) of row. Be careful not to over-apply this solution. This application of boron will produce bigger seeds and flower heads. Do not apply boron to other garden plants. When the back of the flower head turns yellow, it is ready to be cut from the plant.
Sunflowers planted near rows of corn are said to increase yields. Sunflowers can be used to draw heavy metals, toxins, and even radiation from soil, but should be burned at the end of the season if grown for this purpose. Plant sunflowers amid squash plantings to improve pollination and overall production.
More on Companion Planting.