Black oil sunflowers are a type of oilseed sunflower known for their small, black seeds that are rich in oil. These sunflowers are primarily cultivated for oil production and bird feed, making them a favorite among bird enthusiasts. They typically reach heights of 5 to 7 feet and produce striking yellow flowers that measure between 4 to 8 inches in diameter (Gardeners Path).

Growth Characteristics

Height: Black oil sunflowers generally grow to be between 5 to 7 feet tall. However, some gardeners have reported growing them to heights of around 4 to 6 feet when using seeds from bird feeders (Bogleheads Forum).
Flower Size: The flowers of black oil sunflowers are large and bright, contributing to their ornamental value in gardens.
Seed Production: They produce numerous seeds, which are a great source of food for birds like cardinals and finches due to their high oil content and smaller size (Gardeners Path).

To ensure healthy growth and optimal height, it's important to provide the right growing conditions:

1. Soil Requirements

Black oil sunflowers thrive in well-draining, organically rich soil. They prefer slightly acidic to neutral pH levels.

2. Sunlight

These sunflowers require a full sun location, ideally receiving at least 6 to 8 hours of sunlight each day.

3. Planting Depth

When sowing the seeds, plant them about 1 inch deep. If the soil is cool, you may want to plant them a bit shallower, around 3/4 of an inch deep (Gardeners Path).

4. Spacing

Space the seeds 8 to 12 inches apart to allow for adequate air circulation and growth.

To help your black oil sunflowers reach their full potential, consider the following care tips:

Watering: Newly germinated seedlings need consistent moisture. Water them daily for the first week or two, then reduce to once a week during hot weather. Once established, they can withstand some drought conditions (Gardeners Path).
Mulching: Apply a 2-inch layer of mulch to help retain moisture and suppress weeds.
Pest Management: Watch for common pests such as aphids and weevils. Implement organic pest control measures if necessary.

Black oil sunflowers are not only a beautiful addition to any garden but also serve as a valuable food source for birds. With their impressive height of 5 to 7 feet, they can make a striking statement in your landscape. By providing the right growing conditions and care, you can enjoy the vibrant blooms and the joy of watching wildlife flock to your garden. Whether you're planting them for their seeds or their beauty, black oil sunflowers are a rewarding choice for any gardener.