Dahlias are tubers, which means they are typically planted as bulbs rather than from seed. When it comes to sunlight, these flowers are demanding — requiring six to eight hours of direct sun exposure each and every day for optimal growth. While dahlias are technically perennials, anyone in a USDA hardiness zone colder than 8 will need to treat them as annuals. This means replanting new dahlias each year or digging up your bulbs and sheltering them in your basement or garage over the late fall and winter.

Once you’ve chosen a spot with full sun exposure, plant your dahlia bulbs one to three feet apart (depending on their expected size) in well-draining soil. You may add compost or bonemeal to the soil, but do not water the bulbs. Instead, wait for new growth to emerge to begin a watering schedule of two to three times per week. Low-nitrogen fertilizer can be used monthly and aggressive deadheading is recommended to encourage more blooms. 

Source: housedigest.com