The ideal time to plant dahlias is in the late spring, typically between mid-April to May, when the danger of frost has passed. This timing allows the soil to warm up to at least 60 degrees Fahrenheit, which is the optimal temperature for dahlia tubers to start growing. Dahlias need a growing season of at least 120 days, so planting them in late spring ensures they have enough time to bloom and thrive. Remember, dahlias are sun-loving plants, so choose a spot in your garden that gets at least 6-8 hours of sunlight each day for the best results.