I'll admit it, I've likely purchased/ propagated more dahlias than our beds will accommodate. One just can't resist the flashy pictures in the catalogs that arrive in the dreary days of winter. These merchants have us figured out; send beautiful photos of robust gardens, flowers, and all manner of flora just when we are most vulnerable...the middle of winter.
Please understand, it is MUCH too early to plant dahlias outside in our zone 6b climate. Dahlia tubers simply will not survive a frost, nor will they tolerate cold wet soil.
I've started a good portion of mine indoors, and perhaps you'll enjoy seeing how they're coming along.
The "tuber" is not unlike a potato, they even say that Dahlia tubers are edible (though I've never tried one). Clearly they are a favorite food source of voles, as they have wiped out entire beds of dahlias here at home.
If you search dahlias on YouTube, you'll notice that the British publish a lot of dahlia how-to videos. Because of their short growing season, most gardeners in the UK start their dahlias indoors well before the last frost. Here in Virginia, we can successfully grow dahlias simply by planting the tubers in the ground after all danger of frost (think tomato seedlings).
I'm starting mine indoors not just to get a jump on the season, but to take "cuttings" from the young growth to propagate them into more plants. Dahlias root fairly easily, so it's not impossible to create several plants from one tuber.
Dahlia plants will die back after a hard frost in the autumn, but the energy for next-years growth is stored in the tuber. The adventurous gardener will dig up their dahlias tubers, and store them over winter for planting the following Spring. The tubers are somewhat finicky; they want to be stored in a dark place, that isn't too humid, between 40-50 degrees. You can either store the clump of tubers whole, or wash and divide the tubers before storing them.
Last Fall I washed and divided my dahlia tubers, so waking them up from their winter slumber was just a matter of moving them into a heated space, putting them in pots with moist (not wet) growing mix, and waiting....
If you look closely at the picture above, you can see the green "eyes" just sprouting from the tuber.
The growth is much easier to see on this red stemmed variety.
After a few weeks (it varies by variety), the tuber will send up shoots from the eyes. I wait until they're about 3-4 inches tall, and then I will cut the plant with a sharp knife just below a leaf node.
The photo below shows the dahlias that are ready for cutting.
The node is where the leaf meets the stem. After taking my cutting just below a node, I peel off the lower leaves and dip the stem in a bit of rooting hormone. I "stick" the cutting in a moist potting mix amended with sand (for drainage). In a few weeks the plant will develop roots from that leaf node that you planted below the soil.
The dahlia tuber isn't harmed, rather it keeps trying to push new growth. I'll take cuttings from the plant as long as it is producing healthy growth. Once finished, I'll dispose of the tuber as it is no longer suitable for planting outside.
Here you can see where the stem had been cut, and the plant is pushing new growth. I'll make cuttings from that growth once it is about 3-4 inches tall.
Below is a tray of cuttings that I am growing.
Here you can see a cutting after 3-4 weeks; notice how many new roots have developed! I will re-pot this cutting into a larger container, and nurture it along until it's time to move outside (early May here).
Not all will survive, but I've had a lot of success taking dahlia cuttings. It is a great way to expand your inventory, or in my case, to sell so that you may enjoy beautiful flowers of your own!
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