I have lots of "oh, these are my faaaaaavourite flowers" moments, but truly, dahlias are where it's at for me. From the first time I saw the most perfect purple dahlia on the cover of a book about 10 years ago (The Book of Dahlia by Elise Albert, fyi), I have loved them dearly.
A couple of years ago I started growing them in our back garden. So far, the sum total of my dahlia care has been deadheading them after they flower, and then cutting them back after the first few hard frosts each winter. Keeping them watered, but only when we water the back lawn in the height of summer... other than that, nada. I have left the tubers in the ground year-on-year, and because we have had relatively mild winters for the past few years, they have kept flowering each autumn.
I want to grow more varieties next year, and I would love to make my plants more productive flowerers, so I am going to take a slightly different approach this year.
First up, the best, most beautiful and succinct resource I have found for dahlia care is Floret's e-book (you can purchase it for around USD$10 here). Floret is an organic flower farm in the Pacific Northwest USA, and the advice in the ebook is based on their experience of large-scale production of dahlias for commercial growing. But don't let that stop you, because even with my tiny number of plants, I have found it so helpful.
Today, I finally got around to digging up the tubers. We have had several months of frosts by now, and even one snowfall, and all the plants are frost-blackened and "dead". I cut them back to about 10cm above the ground, and then carefully lifted them to avoid cutting or damaging the tubers.
Following Floret's advice, I just shook off the excess dirt, snuggled them into a storage crate and popped them in the shed. The tubers need to be covered with dry dirt or sawdust, because if they are left completely exposed they will dry out. By only shaking off the excess dirt, they will be fairly well protected, but I topped them with a bit of sawdust as added protection. The shed acts as a cool room, and stays around 5-10'C all winter, which is perfect for the dahlia tubers to stay dormant.
When it is time to plant them again in late spring, the tubers will need to be divided. Each of those tubers above were originally single tiny ones, and have now sprouted to around 20 tubers per plant, so there will be plenty more plants from our mother stock this year. I'll do a post on dividing the tubers when I do that in spring, before getting them in the ground. Fyi, a good rule of thumb for timing is to put them in when it is safe to plant tomato seedlings out in your area - every place has its own local lore for this, no? Ours is never before Melbourne Cup day. I read recently that in Hobart it's the Hobart Show, but just a short drive away in the Huon Valley it is a couple of weeks later on the day of the Huon Show... anyway, local knowledge rules on these things, and you know you're tempting fate if you try to plant early!