Feeling daunted about planting your dahlia tubers? Don't know which way is up or down? Don't stress - we've got the answer for you. With this guide you'll be able to confidently get your new plants settled into your garden.
What are Dahlia Tubers?
Dahlia tubers are the underground storage structures of dahlia plants. They are swollen roots that store nutrients and energy for the plant to grow and bloom.
Dahlias will only sprout from one end of the tuber - the crown. See if you can spot the eye before planting to help give your tuber the best orientation.
And remember: size doesn't matter with dahlia tubers. Anything bigger than a AAA battery can produce a wonderful plant with plentiful blooms.
Step 1: Choose the Right Location
Before planting your dahlia tubers, select a suitable location in your garden. Dahlias thrive in full sun, so choose an area that receives at least 6-8 hours of direct sunlight per day. A little afternoon shade if you live somewhere hot can also be beneficial.
If you can, choose somewhere with good drainage. Dahlias can rot if left in wet conditions.
Step 2: Prepare the Soil
Prepare the soil by removing any weeds or debris and add your chosen amendments. We always recommend a good quality compost to help the soil structure and to feed the soil.
If the soil is compacted you might try using a broadfork to improve drainage.
Add a mulch if you can - sugar cane, pea straw, and lucerne are great choices. This will do wonders for your soil and can also have the benefit of keeping roots and tubers cool and retaining moisture in dry conditions. And - big win - they can reduce weed pressure considerably.
You can also add the mulch after planting. We recommend it to be done earlier if the patch will sit fallow for a period of time.
Full disclosure: we don't mulch our dahlias in an ordinary year. For us as a farm the economic benefit/burden means it is not worthwhile. It is something we are considering this year due to the predicted very dry and hot conditions.
Step 3: Planting the Tubers
Plant the dahlia tubers horizontally, with the eye or bud facing upwards.
The eye is a small, pointed bud located on the tuber.
Place the tubers about 10-15cm deep in the soil, spacing them at least 30cm apart.
When considering your spacing it is important to keep your particular climate in mind. A close spacing will work better in a dry environment, while a slightly larger spacing will be better in humid conditions. If you plant very close you may need to remove lower leaves through the season to promote airflow.
We plant at a 40cm spacing and do 2 rows in a 1m wide bed (all of our beds across the flower field are the same size). In a bed of 10m square we fit approximately 50 tubers.
Step 4: Watering and Mulching
After planting you can water to settle the tubers.
Then, typical advice is to not water again until the plants are 10-15cm out of the ground.
Use your judgment. This advice applies in normal or wet years when there is rain in spring, the soil retains a level of moisture, and it is not scorching hot.
If conditions are unusual - as predicted for spring/summer '23 then you may have to add water from time to time.
An easy way to test is to put a finger in the soil and feel it. If moist leave it be, if dry add some water.
Once the plants are out of the ground you can add mulch (if desired and not already done).
Step 5: Provide Support
As dahlia plants grow, they may require support to prevent them from bending or breaking. Install stakes or cages around the plants at the time of planting to avoid damaging developing roots and tubers later.
Another option is to net or use the corral method.
In this way you place your stakes around the perimeter of the bed. For netting add floral mesh or wire suspended horizontally above the bed.
To corral run a string around the perimeter of the stakes to create a little dahlia pen. Usually two or three layers.
This will help keep the plants upright and protect them from strong winds.
We do not support as a general rule. Our patch is quite protected from the wind and our tight spacing allows the plants to support each other. We also see losing a branch or two through the season as an ok trade for not spending the time adding a support system.
Step 6: Fertilizing
To promote healthy growth and abundant blooms, fertilize the dahlia plants regularly. They are hungry plants!
We never use synthetic fertilisers, and will no longer be using chemically enhanced or fortified fertilisers. Organic pelletised chicken manure is great. We also use rock dust, compost, and molasses to feed the microbiome and allow our soil to provide essential nutrients to our plants.
Something to note: too much nitrogen will give you dahlia plants that are big, bushy, and green with not so many flowers. In the later season too much nitrogen can also cause tubers to not store well. For this reason we don't add nitrogen once the plants are blooming, only potash.
That will encourage flowers, tuber development, and better storage.
Step 7: Pest and Disease Control
Monitor your dahlia plants for any signs of pests or diseases.
Common pests include aphids, mites, caterpillars, slugs, and snails. Use controls of choice to protect your plants.
A note on mulch: it can harbour slugs and snails. Make sure it isn't up against the trunk of the dahlia and keep a particular eye out for these guys when plants are newly sprouted.
Virus is a whole thing and deserving of its own post. As a general rule if you see virus the plant should be pulled and destroyed - in the garbage and not the green waste.
Step 8: Enjoy the Blooms
With a little love and a lot of patience your dahlia tubers will grow into beautiful plants that produce stunning blooms. Don't forget to stop and enjoy the beauty you have grown.