The weeks around Melbourne Cup Day (first week in November) are usually given as a guide for planting tubers.
Planting can continue from mid October right through November and still give you blooms for exhibition in February. Some expert growers advise gardeners not to plant tubers during a waning phase of the moon cycle so this may influence whether you plant in late October or early November.
It is a good idea to incorporate a complete fertiliser about two to three weeks before planting. Don’t put fertiliser in the planting hole but make sure the fertiliser is incorporated into the soil before planting.
Except for smaller varieties, dahlias need support, usually by staking. Plant the stake first to eliminate the chance of damaging the tuber. Many growers plant a tuber on each side of one stake. Label the stakes as you plant. Try to adopt a systematic routine – it is easy at this stage to mix up the tubers.
Look for the eye or shoot on each tuber. Plant the tuber horizontally, about 10cm deep with the eye about 5cm from the stake and slightly higher than the tail. If you are planting several tubers, space them about 60cm apart to give them room to grow. Allow space to get access if you have multiple rows of plants.
Plant into moist ground – water in with a little dilute seaweed solution if it is dry – and DO NOT WATER IT again until the shoot is at least 15cm above the ground unless the soil dries out. Until it has established its own root system the dahlia usually gets all it needs from the tuber. Watering earlier risks rotting the tuber.
Big or small tuber? Interestingly the smaller tuber is better because it will develop its own root system far quicker than the big tuber which continues to draw from its stored food. As the weather warms up, the plant with its own independent root system will be more resilient than the plant growing from the big tuber.