Here are a few popular self-seeding plants to consider for your garden:

Nasturtiums: These flowers are annuals in most climates, meaning they complete their life cycle in one year.
Hardiness Zones: 9-11
Sunlight: Full sun to partial shade

Sunflowers

Nigella (Love-in-a-Mist): Planted these in my fairy garden. They are delicate blue or white flowers surrounded by feathery foliage creates a charming and ethereal look.
Hardiness Zone: 2-10
Sunlight: Full sun to partial shade

California Poppies: Vibrant orange, yellow, or red blooms that thrive in sunny and dry conditions, adding a burst of color to your garden.
Hardiness Zone: 6-10
Sunlight: Full sun

Cosmos: With their daisy-like flowers in various shades of pink, white, and purple, Cosmos attracts pollinators and adds an airy elegance to the garden.
Hardiness Zone: 2-11
Sunlight: Full sun

Cleome (Spider Flower): Tall spikes of unique spidery blooms in shades of pink, white, or lavender create a striking vertical element.
Hardiness Zone: 2-11
Sunlight: Full sun to partial shade

Larkspur: Tall spires of colorful flowers in shades of blue, purple, pink, and white, perfect for adding height and vertical interest.
Hardiness Zone: 2-9
Sunlight: Full sun

Forget-Me-Nots: Small, delicate blue flowers that form a carpet of color, often used for shaded areas and woodland gardens.
Hardiness Zone: 3-8
Sunlight: Part shade to full shade

Borage: Bright blue, star-shaped flowers and edible leaves that attract pollinators while adding a touch of flavor to salads.
Hardiness Zone: 2-11
Sunlight: Full sun to partial shade

Sweet Alyssum: Fragrant white, pink, or purple flowers that form low mounds, suitable for borders, containers, and hanging baskets.
Hardiness Zone: 4-9
Sunlight: Full sun to partial shade

Poppies: Various types of poppies, such as Oriental poppies or Shirley poppies, produce eye-catching blooms in a range of colors.
Hardiness Zone: Varies by type (e.g., Oriental poppies are often Zone 3-8)
Sunlight: Full sun

Black-Eyed Susan: Bright yellow flowers with dark centers that attract butterflies and other pollinators.
Hardiness Zone: 3-9
Sunlight: Full sun to light shade

Verbena Bonariensis: Tall, slender stems topped with clusters of small purple flowers that create a whimsical and see-through effect.
Hardiness Zone: 7-11 (often grown as an annual in colder zones)
Sunlight: Full sun

Hollyhocks: Towering spikes of flowers in a variety of colors that add a cottage garden charm to any landscape.
Hardiness Zone: 3-9
Sunlight: Full sun to light shade