When your rooted cutting arrives unpack it immediately and give it a good drink. We recommend that you then pot this into a 9cm ( or similar size ) pot and grow it on until all risk of frost has passed when you can then plant it out.
Organic material is important for dahlias as they are a tuberous plant. Ideally, incorporate plenty of well rotted manure into the growing area as early in the year as possible. This gives time for winter weather to breakdown the material.
Ensure that all of the previous year's plant material is removed to prevent disease being carried forward. 
One month before planting the ground should be worked again to aerate the soil and break up any large clods.
Planting times vary depending on location. South of Birmingham planting can take place in mid May, further North planting should be delayed up to mid June. Young plants need protection from frost.
For individual plants, holes for planting should be 6 inches deep 3 ft apart. If it is planned to stake the plants, it is important that the stake is hammered into the ground at this stage to avoid damaging the tuber by running a stake through it.
Place the tuber in the hole laying longwise on its side, with the sprout or eye facing up. If the tuber has a sprout an inch long or more, care should be given not to damage the fragile shoot. However, if this does happen, auxiliary eyes at the base of the broken shoot will grow.
If planting cuttings that have been grown on, or indeed tubers that you started in pots, carefully remove the plant from the pot and plant to the level of the root ball.
Tie a name-tag on your stake so you will know later which plant is growing there.
Once planting is complete and the bed marked out a top dressing of a general purpose fertilizer such as Growmore or or for those organic gardeners bone meal, is all that is required. Gently work this into the top inch of the ground.
Water dry tubers well and keep them moist