Dahlias generally take about 12 to 16 weeks (approximately 90 to 100 days) to start blooming after planting the tubers in the ground

. Once they begin to bloom, dahlias will continue to produce flowers throughout the summer and fall until the first frost, which typically occurs around October or November in many regions

. The blooming period can last several months, often from mid-summer (around July) through to the first frost, providing a long flowering season

. The exact timing and length of bloom depend on factors such as the dahlia variety, climate, temperature, and care conditions

. In summary:

• Time to first bloom: 12 to 16 weeks after planting (about 90-100 days)

• Bloom duration: Continuous blooming from first flower until first frost, often several months (summer through fall)

This makes dahlias a long-blooming flower that can brighten gardens for an extended period during the growing season.