Dahlias are native to Mexico and thrive is warm temperatures. While dahlias don’t tolerate extreme cold conditions, in New Zealand they are grown as perennials, going dormant over winter and re-emerging once temperatures warm.
Plant out new tubers in early spring once the risk of frost has passed. This is also a good time to dig and split older tuber clumps which is recommended every 2 - 3 years.
Dahlias like a sunny site that also offers wind protection. Staking larger varieties is recommended. When doing so, position stakes before planting the tubers.
As with all gardening, soil health is everything. Dahlias require well draining yet moist soil as they are prone to rotting they do not like wet feet. Preparing soil with a good dose of organic compost will help your dahlias thrive.
Plant tubers with the eye facing upwards spacing 90cm apart with 10cm soil cover. A good covering of mulch will help keep your soil moist in summer while also suppressing weeds and encouraging air flow.
Pinching out your dahlias when they have 2-4 sets of leaves will result in bushier plants and greater flower production. Disbudding is also recommended in order for flowers to reach their full potential.
For cut flowers, always bring the water to the plant and place cut flowers directly in the water. Doing this first thing in the morning will extend vase life. A good drink of water the night before picking also helps here. Unlike other flowers, dahlias will not continue to open once picked, so choose flowers that have fully opened. Display out of direct sunlight in a cool place.
While there is differing advice relating to over wintering your dahlias, the right answer depends on your growing conditions, soil and location. Here on the farm we get relatively heavy frosts so we add a good thick layer of mulch for protection over winter. We use pine needles, pea straw, leaf matter and bark mulch.
There are more than 50,000 cultivars growing all around the world, different countries have slightly varied classifications and widely different growing conditions. The world of dahlia growing can be a deep rabbit hole of conflicting advice and endless reading and wish lists. It is always important to know your growing conditions to gain the best result. You should contact your local dahlia society for the best advice and a wealth of knowledge relative to your location.