Dahlias are one of the easiest and most spectacular flowers you can grow in your garden. From mid-summer to first frost, they will flower almost continuously. Dahlias will grow in an area where there is some shade, but the plants will be taller and you’ll typically get fewer flowers. The package your dahlia tubers came in can provide valuable information about your dahlia, including height. Large dinnerplate dahlias can easily reach 4' in height. Flower stalks this tall need to be staked. It’s best to place the stake when you plant your tubers.