Dahlia Planting Instructions
Garden site
Dahlias need full sun (at least 8 hours daily) to perform at their best and give lots of blooms.  Choose a sunny garden spot with freely draining soil, or if necessary raise the garden bed to provide adequate drainage. 
Dahlias perform at their best if the  soil has had at least 5 to 10 cm of quality compost/well-rotted manure, some blood and bone and a dusting of  fertiliser worked into it, prior to planting.Your Dahlias will also need staking to stop them falling over from the weight of their flowers and in strong wind. If you have a few plants, place tall, sturdy stakes next to the tubers at planting time so you can tie stems to them as they grow. For large scale borders or flower farmers, the corral method works well, which uses  a metal T-post placed roughly every 2.5 m along the outside edges of the beds and then stringing a double layer of bailing twine from post to post around the bed to support the plants.
Once you receive your tubers, store in a cool, dry place indoors or under cover until all danger of frosts has passed. No tubers should be planted into waterlogged soil, either in the garden or pots.  Excessive Spring rains in your area may mean it is best to delay planting until the ground is consistently suitable. .
When it’s time to plant, dig holes or trenches around 10-15cm deep and  the tubers get placed on their sides, with the growing eye/shoot facing upwards. Allow a space of 30-40cm between tubers, then cover with soil. Do not commence watering until the first green shoots come up.
Ensure your Dahlias get watered consistently through the growing season. Soaker hoses are perfect or if not available water by hose at soil level, avoiding the foliage. After your  plants reach around 30 cm tall it's time to pinch them, which means snip 7 to 10 cm off of the growing centre to encourage low basal branching, which increases the flower production and the overall stem length.
Watch out for  Slugs/snails/earwigs/nematodes. All these can damage the young plants/flowers/tubers.
Cut flowers
After all your hard work, your tubers will reward you with an abundance of beautiful blooms. Although not hugely long-lasting cut flowers, you should get 5 to 7 days from stems cut at the proper stage. Dahlias don't open much after they’ve been harvested, so it’s important to carefully pick them when they are almost fully open, but not overly ripe. Check the back of each flower head, looking for firm and well hydrated petals. If they are papery or slightly dehydrated this means the flowers are aging and won’t last in the vase. Once indoors make a fresh horizontal cut at the bottom of the stem and place the ends into a vase of very hot (not quite boiling) water. Let the stems stay in the water for at least one hour. Floral preservative also helps extend vase life.