Want to get a head start on your dahlia plants for the season? Want to test your tubers for viability? A pre-sprout test is the way to go.
First, I will talk about the fastest way to test for tuber viability. Perform a pre-sprout test for viability if you are not sure that your tuber has eyes. I basically never do this on the farm. This is simply because I can tell which tubers are going to grow, just by inspecting their eyes. Of course, this takes some practice. You can learn how to identify eyes on your dahlia tuber, here.
Still aren’t sure? Then a pre-sprout test is the best way to give the dahlia a chance to prove its abilities.
Second, I will share a great way to get a head start on your dahlias for the year. Start dahlias in pots in a protected space. Then, transplant them out into the garden. You could get blooms around 4-6 weeks earlier than otherwise.
Note that when you begin any type of pre-sprout test on your tubers, you have activated the growth of the tuber’s eyes. This means you can no longer return them to storage in a cool dark place. In other words, they must be planted and cared for. This is a pretty good reason to not start this process too early. Unless you are happy to have some dahlia houseplants (or greenhouse plants) until your “last spring frost date” (frost safe date).
To Test Your Tubers for Viability
First, find a tray or container that will hold about six inches of soil. Put this tray in a place where the soil temperature will not drop below 60 °F/ 16 °C. Next, spread about two inches of lightly dampened soil along the bottom. Be sure that the soil is not too wet, otherwise the tubers will rot.
Then, line up all of your tubers horizontally. Be sure to label and keep track of which tuber is which. At this point, space does not matter, because the tubers will be transplanted. So, you can put a ton of tubers into this container.
Cover them with the remaining soil so there is about an inch on top. Do not water, assuming you started with damp soil. Remember, dahlia tubers are very prone to rotting. Note that it is better for the soil to be on the dry side, than on the wet side (once you have a growing plant, water regularly, of course).
Your dahlia tubers will quickly begin to sprout. In a week, dig out the tubers and see what’s happening. Bury the ones that haven’t sprouted eyes. Give them another week, and check again. Give up on tubers after 3 weeks of no sprouts. Eyes can be white, pink, or purple.
Immediately transplant the sprouting to deeper pots, so the tubers are covered in about five inches of soil. Be sure to time this correctly. If they are not moved to a more permanent home (outside into the garden, or perhaps to a deeper container, planted 5 inches deep), then they will grow leaves at a shallow depth and will not make healthy plants.
Remember, when you transplant them, use lightly damp soil and do not water until growth begins to appear. Plant the sprouting tuber 5 inches deep, horizontally. Once the leaves pop out of the soil surface, begin watering regularly.
To Get a Head Start on Your Dahlia Season
If you want to get a head start on your dahlias, consider planting your dahlias into small pots. I use one gallon pots. Larger will work well too. Dahlias need to be started in an environment where soil temperatures will be maintained at or above 60 °F/ 16 °C. They also need access to sunlight as soon as they begin to sprout out of the ground. A greenhouse, hoop house, or sunny windowsill are great places.
It typically takes about two to four weeks for dahlias to begin to sprout up out of the soil. So start this process between five and seven weeks before when you expect to be able to plant them outside.
This method is best for people with smaller amounts of dahlias, just because this is a lot of extra labor for the dahlia farmer. The benefit is that you will get blooms typically 4-6 weeks earlier. Other options for getting blooms earlier include planting in raised beds, under floating row covers, or in hoop houses.
Start with about two inches of damp soil. Again, remember not to use soil that is too wet. Otherwise, your tubers will rot before they establish a root system. Plant the tuber horizontally with the eye facing up toward the sky.
Cover in five inches of soil. Do not water until greens begin to appear.
Once your outdoor soil temperatures have warmed to 60 °F/ 16 °C, transplant your happy dahlia plants out into your garden.
Why I Don’t Normally Do This
I simply have too many dahlias at the farm to start in pots and transplant out. It cost me a lot in time and materials, and does not give me enough of a head start to make it worth it. If you have a smaller dahlia patch, want dahlia blooms earlier for a wedding or event (perhaps a fair or bloom competition), or want a dahlia container garden that impresses your neighbors, then a pre-sprout might be worth the effort!