Tubers are the roots of mature plants and look like a cluster of brown, carrot-like roots joined by the previous years dried stem. You can buy them from garden centres or by mail order in spring, or use your own tubers that you have overwintered.
Dahlias will come back every year, but if you live in an area with cold winters, its best to move them indoors in autumn. Those planted in pots can simply be moved to a frost-free spot, such as an unheated greenhouse. For dahlias growing in the ground, you will need to lift and store the tubers and store them in a pot of dry compost. Then, in spring, replant the loose tubers in the ground and refresh the compost of potted dahlias to give them a fresh burst of nutrients necessary for a good summer display.
As a dahlia enthusiast I always look forward to the first blooms of the season. There’s nothing quite like seeing those vibrant flowers begin to open up. However dahlias are notoriously slow to emerge in spring. Their tubers need warm soil to send up new growth. That means you often have to wait until well after your last expected frost date to plant them.
Luckily there are some tricks to sprout dahlia tubers early and get a head start on the season. By pre-sprouting indoors you can enjoy flowers 4-6 weeks sooner!
In this comprehensive guide, you’ll learn all about:
- The benefits of sprouting dahlia tubers early
- Step-by-step instructions for the sprouting process
- Tips for testing tuber viability before planting
- How to care for sprouts until it’s time to transplant
Let’s dig in so you can enjoy an earlier bloom season!
Why Pre-Sprout Dahlia Tubers?
Getting a jump on the growing season offers a couple key advantages:
Earlier Blooms
The most obvious benefit is earlier flowers. Sprouting tubers indoors while soil is still cold allows more time for root growth. Those established roots can better support growth when planted outside.
With a 4-6 week head start, your dahlias will be that much more mature once transplanted. Healthier plants produce more and earlier blooms.
Assess Viability
Not all stored dahlia tubers survive winter in good shape. Some may rot or shrivel up during storage.
Sprouting tubers in advance lets you test which are still viable. You can toss out any non-sprouting tubers and avoid wasting garden space on them.
When to Start the Sprouting Process
Timing is key! Plan your sprouting schedule around your average last spring frost date.
Ideally, aim to transplant sprouts into the garden 2-3 weeks before your expected final frost. Avoid starting too early indoors – sprouts may stretch and become leggy after 4-5 weeks.
For example, if your last frost date is May 15th, begin sprouting tubers in mid to late April.
Step-By-Step Guide to Sprouting Dahlia Tubers
With the right setup, pre-sprouting dahlia tubers is easy. Just follow these steps:
Gather Your Supplies
To start, you’ll need:
- Dahlia tubers – stored from last year or newly purchased
- Trays or small pots with drainage holes
- Fresh growing medium like potting mix
- Plastic bags or sheeting (optional)
- Plant labels
Provide Warmth and Light
Recreate summer conditions as best you can:
- Maintain temperatures around 70°F – 75°F for optimal sprouting. Tubers need warmth.
- Place trays near sunny windows or under grow lights once sprouting begins. Light prevents leggy growth.
Plant Tubers Horizontally in Trays
- Fill trays with 2-3 inches of damp (not soggy) potting mix.
- Arrange tubers flat, 2-3 inches apart, with the eye facing up.
- Cover tubers with 1-2 more inches of mix.
Label Each Variety
- Use plastic or wooden plant labels to mark each dahlia variety. Proper labeling prevents confusion later.
Cover Trays and Monitor Progress
- Enclose sprouting trays in clear plastic to retain moisture.
- Check daily and remove covering once sprouts emerge.
- Water carefully as needed to keep mix moist but not soaked.
Transplant Mature Sprouts
- Gently dig up sprouted tubers when shoots are 2-3 inches tall.
- Transplant into pots, burying stems while keeping leaves uncovered.
- Continue growing indoors until it’s planting time outdoors.
Testing Tuber Viability
If you’re uncertain whether stored tubers will still grow, pre-sprouting lets you find out quickly.
Follow these tips for sprout testing:
- Begin testing tubers 8 weeks before your target outdoor planting date.
- Use shallow trays filled with just 2 inches of damp potting mix.
- Bury tubers horizontally right below the mix surface. Don’t cover them.
- Check weekly for sprout development.
- Discard any tubers that haven’t sprouted after 3-4 weeks – they likely won’t grow.
- Once sprouting begins, transplant immediately into deeper pots.
If a tuber sprouts, you know it’s viable and safe to plant!
What Do Dahlia Sprouts Look Like?
Watch for small bumps emerging from the tuber’s “eye” area. Young sprouts may be white, pink, or purple before turning green.
Mature sprouts will be green with yellow-green leaves. Transplant sprouts once they reach 2-3 inches tall and have some leaves.
Caring for Pre-Sprouted Dahlias
With a little extra care, you’ll have strong transplants ready to thrive when planted:
- Provide ample warmth and sunlight until it’s time to plant outdoors.
- Monitor soil moisture closely. Water carefully to prevent rotting.
- Transplant into larger containers as needed to support growth.
- “Harden off” sprouts before transplanting outside.
- When planting, bury pre-sprouted tubers at the same depth they were grown indoors.
Enjoy an Earlier Bloom Season!
While not mandatory, pre-sprouting dahlia tubers can give your plants a big advantage. You’ll find out which tubers are still viable after storage and have mature transplants ready to pop into the garden weeks earlier.
Just be sure to give sprouting tubers proper care, especially plenty of warmth and light. Avoid overwatering that can quickly lead to rot. With some simple preparation, you’ll be rewarded with earlier and more plentiful dahlia blooms!
Growing dahlias in pots
Many varieties of dahlia can be grown in pots all year round, providing a splash of colour on patios and balconies. Small to medium-sized dahlias, such as mignon and ruff dahlias, as well as slow-growing water lily, ball and pompom dahlias, do well in containers. Avoid growing cactus dahlias, which can grow to over 2m in height – as a general rule, only grow dahlias which dont usually require staking.
Grow potted dahlias in a warm, sunny and sheltered spot, protected from strong winds. Water regularly and feed with a phosphate-rich liquid fertiliser once a week.
Use free-draining, peat-free compost and plant the tubers about halfway down, so that the buds on the tuber shafts are only lightly covered with soil. Water well. Pinch out the shoots when theyre around 10cm long, to encourage bushy growth.
- Dahlia tubers
- Large pots
- Peat-free multi-purpose compost
- Plant labels
- Pen
Total time: 30 minutes
When planting dahlia tubers, ensure the joint where the roots meet the stem is facing upwards. Label your pots and grow on in a greenhouse or sunny windowsill. Keep the tubers well watered.
Pinch out the tips of the main shoot, down to the top pair of leaves. You also need to remove most of the shoots growing from the tuber, except for five. This encourages bushy plants, strong, vigorous growth and a lot more flowers.
When all risk of frost has passed, harden off your dahlias by placing them outside during the day and bringing them in at night. After a week they will be ready to plant out into their final growing positions.
When to plant dahlia tubers
Starting dahlias in pots is a great way to get them into growth earlier in the season. Simply plant dahlia tubers in large pots filled with peat-free, multi-purpose potting compost in March or early April, and then keep them on a windowsill or in a frost-free greenhouse until late May, when its safe to plant them outside.
Starting off dahlia in pots will also encourage them to develop more quickly, so theyre likely to start flowering earlier. Before planting, soak the tubers in a bucket of tepid water for an hour so they can fully rehydrate.
96. Pre-sprouting Dahlia Tubers
FAQ
How to encourage dahlia tubers to sprout?
Put in a really warm spot in your home (next to a radiator or heater, a sunny window, or under grow lights where heat radiates from the lighting). This is a simple way to wake up your dahlia tubers before planting outside so they sprout sooner.
How long do dahlia tubers take to sprout?
Often, the tubers don’t sprout until they have been in the ground (or in a pot) for 4 to 6 weeks. It takes tubers longer to come out of dormancy when they are planted early in the season and the weather is cool. Sprouting happens more quickly when you’re planting late and the soil is already warm.
How to tell if dahlia tubers are alive?
In short, when you are looking at dahlias that seem dried out, it does not mean they will not be viable. You can tell by the feel of the tuber if there is still moisture inside and as long as they are not dried out, they will be fine.