Where to Plant
Dahlias should be planted after threat of frost has passed. Dahlias need a sunny location to thrive. In our hot and dry climate, plant where they will receive morning sunlight, afternoon shade.
Dahlias are perennial. Once blooming has ended [usually around November], you can simply leave the plant where it is, remove all vegetation and it will return even stronger the following year. No need to dig up tuber [root ] in our climate. If however, you are growing in an area that gets snow, you may need to dig up tuber.
soil * Planting* Fertilizer
Ground should be warm, well drained at planting. If you have a heavier soil, add in sand or peat moss to lighten and loosen the soil texture for better drainage. Organic potting mix used for growing veggies soils can be used to amend soil as well.
To transplant, dig hole deep enough to bury root ball just even with your soil with a couple of extra inches of room on the sides. Add fertilizer to the bottom of the hole.
As for fertilizer, dahlias do not need extra nitrogen [the first number of your blend]. What they need to produce abundance of glorious blooms is phosphorus and potassium. Look for a blend something like a 5-10-10, 10-20-20, or 0-20-20.
First applications should be at planting then repeated again approx. 3-4 weeks later - About 1 time per month is ideal.
Water * Support
Deep water every other day on average for 30 minutes. When temperatures go above 100 degrees, you may need to water more frequently.
Dahlias get TALL so providing support is vital. Stakes [like for tomato growing] and a bit of twine work well.