Black oil sunflower seeds, commonly known as BOS, are a widely available type of sunflower seed that can be planted and successfully grown into mature plants. These seeds are a variety of the common sunflower, Helianthus annuus. They are characterized by their thin shell and high oil content, which makes them a popular, nutritious food source for wild birds. While often bought in bulk for bird feeders, the seeds retain their agricultural viability. Success depends on understanding a few key differences between birdseed and dedicated planting stock.
Understanding Seed Viability
The biggest factor influencing the success of planting black oil sunflower seeds from a birdseed mix is the seed’s viability, or its ability to sprout. Birdseed is not regulated or stored with the same germination standards as seeds packaged for gardening. This can lead to lower sprouting rates due to age or poor storage conditions. Seeds that are too old or have been exposed to extreme temperature fluctuations may have damaged embryos, preventing them from growing.
Germination Test
To check the quality of a batch of seeds, a simple germination test can be performed. Count out ten seeds and place them on a damp paper towel. Fold the towel over the seeds and slide it into a sealed plastic bag to maintain moisture. Keep this bag in a warm location for about one week, checking regularly for sprouts. If seven out of the ten seeds sprout, the batch has a 70% germination rate, indicating it is a good candidate for planting.
Planting and Growing Instructions
Sunflowers are easy to grow, and black oil seeds should be direct-sown into the garden after all danger of frost has passed. The soil temperature needs to be at least 50°F for optimal germination, though waiting until the soil warms to 60°F or 70°F often yields faster results. These plants thrive in full sun, meaning they need at least six to eight hours of direct sunlight each day.
The seeds should be planted approximately one inch deep into well-draining soil, which accommodates their deep taproot. Space the seeds about 8 to 12 inches apart, or even further if you anticipate very large plants. Once the seeds are sown, water the area thoroughly to ensure good seed-to-soil contact, which is necessary for germination.
Initial watering should be consistent until the seedlings are established, often requiring daily moisture, particularly in dry conditions. Once the young plants have developed a few sets of true leaves, they become quite drought-tolerant and can be watered less frequently. Fertilization is generally unnecessary, as sunflowers are not heavy feeders, and excessive nutrients can sometimes reduce seed yield. If multiple seedlings sprout very close together, thin them out by removing the weaker ones to ensure the strongest plant has adequate resources.
Expected Characteristics of the Mature Plant
The black oil sunflower variety typically grows into a tall plant, commonly reaching heights between five and ten feet. They are fast-growing annuals, often reaching full maturity and producing seeds within 60 to 100 days of planting. They are excellent for creating a natural screen or backdrop in a garden.
The flowers are generally single-headed, producing bright yellow petals surrounding a central disk. Flower heads are usually moderate in size, ranging from four to eight inches in diameter. Due to their significant height and the weight of the developing seed head, the stalks can become top-heavy as the plant matures. It is wise to provide support, such as staking the plant, once the stalk reaches about three feet tall to prevent bending or breaking in strong winds. Gardeners can harvest the seeds for oil pressing, human consumption, or simply leave the seed heads on the stalk for visiting birds.