Most gardeners buy dahlia tubers. It's the conventional wisdom — walk into a nursery in spring, pick up a fat, knobby tuber, plant it, and wait for the blooms. And it works. But what if you grew your dahlias from seed instead? And then, at the end of the season, harvested your own tubers to replant next year? That's exactly what we did at Diamond Field Blooms, and the results genuinely surprised us.
Growing dahlias from seed is the road less travelled — and for good reason. It requires more patience, more attention in the early weeks, and a tolerance for unpredictability. But the rewards are significant, and for the budget-conscious or adventurous gardener, it opens up a whole new relationship with one of South Africa's most spectacular summer flowers.
Starting from seed: what to expect
Most dahlia varieties don't come true from seed. Unlike heirloom tomatoes or sunflowers, where seed-saving reliably reproduces the parent plant, dahlias are complex hybrids. The seedlings you grow from a single packet of dahlia seeds will each be genetically unique — different flower forms, different colours, different plant heights. That unpredictability is either frustrating or thrilling, depending on your outlook. We lean firmly toward thrilling.
Sow dahlia seeds in late winter to early spring (July–August in most of South Africa) indoors in seed trays, in a warm spot with good light. Use a fine seed-raising mix, sow shallowly at about 5mm depth, and keep the mix consistently moist but not waterlogged. Germination typically occurs within 7–14 days. Once seedlings have two sets of true leaves, transplant them into individual pots and grow on until the risk of frost has fully passed before planting out.
If you want to get started, our Dahlia Seeds are a great entry point — a mix of varieties that produce a range of flower forms and colours, all suited to South African growing conditions.
The growing season: patience rewarded
Seed-grown dahlias take longer to bloom than tuber-grown plants — typically 90–120 days from sowing versus 60–90 days for tubers. That's a meaningful difference in a South African summer, where the growing window can be long but the best blooming weather is finite. Plan your sowing date accordingly so your plants are in full flower during the peak of summer rather than still building up to it.
Once established in the garden, seed-grown dahlias grow with impressive vigour. Pinch out the growing tip when the plant reaches about 40cm — this encourages bushy, multi-branching growth and significantly more flowers. Feed every 2–3 weeks with a potassium-rich liquid fertiliser once buds begin to form. Stake taller varieties early, before the stems become heavy with blooms.
Through the season, you'll discover what each plant has become. Some will produce small, informal pompon flowers. Others might surprise you with large, dinner-plate-style blooms in deep burgundy or coral. It's one of the most genuinely exciting things about growing dahlias from seed — every plant is a reveal. For more detailed growing tips season by season, see our Dahlia Growing Guide for South African Gardens.
The tuber harvest: what we found
Here's where it gets really interesting. At the end of our first growing season — once the foliage had begun to die back after the first cool nights — we lifted our seed-grown dahlia plants. Each plant had produced a clump of tubers at its root base, exactly as a purchased tuber-grown plant would.
Each plant yielded 6 to 10 tubers.
To put that in perspective: you start with one seed worth a few rands, nurture a plant through a single growing season, and end with up to 10 tubers — each one capable of producing a full, blooming plant the following year. From one packet of seeds containing 20–30 seeds, you could theoretically build a collection of 150–300 tubers in a single season. That's not a small thing.
For comparison, a purchased tuber from a nursery typically produces a clump of 5–15 tubers after a full season. A first-year seed-grown plant producing 6–10 tubers is performing on par with, or close to, a purchased tuber — at a fraction of the cost.
Seed vs tuber: a clear comparison
| Seed | Tuber | |
|---|---|---|
| Cost | Very low | Higher |
| Predictability | Variable — surprise blooms | True to named variety |
| First year blooms | Yes, but later in the season | Yes, earlier |
| Tuber yield (year 1) | 6–10 per plant (strong result) | 5–15 per clump |
| Year 2 potential | Excellent — now you have tubers | Excellent |
| Best for | Experimentation, volume, budget | Specific varieties, reliability |
The seed approach makes most sense for gardeners who are comfortable with variability, want to build a large dahlia collection affordably, or simply love the process of growing from scratch. The tuber approach suits those who want a specific named variety — a 'Cafe au Lait' or a 'Bishop of Llandaff' — or who want earlier blooms in their first season.
There's also a third option: use seeds to build your tuber stock over one or two seasons, then use those tubers going forward. This is exactly what we'd recommend for anyone serious about growing dahlias at scale.
What to do with your harvested tubers
Once you've lifted your tubers — ideally a week or two after the first frost or after the foliage has died back naturally — here's how to handle them for the best chance of success next season:
- Clean and inspect: Gently remove excess soil. Check each tuber carefully and discard any that show signs of rot, soft spots, or damage. One rotten tuber in storage can spread and ruin the whole batch.
- Cure briefly: Leave tubers in a cool, dry, well-ventilated spot for 24–48 hours to allow the cut ends to dry and callous over. This reduces the risk of rot during storage.
- Label everything: This is critical. Once dahlias are out of the ground, they all look the same. Note the flower colour, form, and height on a tag tied directly to the tuber clump. Future you will be grateful.
- Store correctly: In South Africa's relatively mild winters, store tubers in a breathable bag, wooden crate, or cardboard box packed with dry vermiculite, coco peat, or crumpled newspaper. Keep them in a cool, dark, frost-free location. Check monthly and remove any tubers showing signs of rot.
- Replant in spring: Once the risk of frost has passed — from August in frost-free regions, September on the Highveld — your tubers are ready to go back in the ground. See our Spring Planting Tips for Dahlias for full guidance on getting them off to the best start.
Dahlias as cut flowers
One of the great pleasures of growing dahlias — whether from seed or tuber — is the cutting garden potential. Dahlias are exceptional cut flowers: long-lasting, richly coloured, and available in an extraordinary range of forms from tight pompon to loose, anemone-centred dinner plates.
Cut dahlias in the early morning when the blooms are fully open but before the heat of the day. Place immediately in deep, cool water and allow to condition for several hours before arranging. They'll last 5–7 days in a vase — longer if you change the water every couple of days and re-cut the stems at an angle.
Pair them with zinnias, cosmos, or sunflowers for a lush, abundant summer arrangement. If you want to build a proper cutting garden around dahlias, our guide to creating a cutting garden from seed is a good place to start planning.
The bottom line
Growing dahlias from seed and harvesting your own tubers is one of the most rewarding projects a South African gardener can take on. It's budget-friendly, endlessly surprising, and by the end of your first season you've gone from a handful of seeds to a full collection of tubers ready for next year — each one a plant you raised yourself.
The unpredictability that puts some gardeners off is, for many of us, the whole point. Not knowing exactly what you'll get is what makes that first bloom, when it finally opens, genuinely exciting.
Ready to try it? Shop our Dahlia Seeds and start building your own tuber collection this season.
Frequently Asked Questions
Do dahlias grown from seed produce tubers in their first year?
Yes — in most cases, seed-grown dahlias will produce a modest clump of tubers in their first season. The size and number of tubers depends on growing conditions, how long the plant had to establish, and the variety. In South Africa's warm climate, 6–10 tubers per first-year plant is a realistic and strong result.
Will dahlias from seed look the same as their parent plant?
Usually not. Most dahlias are complex hybrids, meaning seeds produce genetically unique offspring. You may get a completely different flower colour, form, or size than the plant the seed came from. This is part of the appeal — but if you want a specific named variety reliably, purchase tubers instead.
When should I sow dahlia seeds in South Africa?
Sow indoors in July or August — 6–8 weeks before your last expected frost date. This gives seedlings time to develop before they go outside. In frost-free regions, you can sow earlier or directly into the ground. Seed-grown dahlias generally bloom 90–120 days after sowing, so earlier sowing means earlier flowers.
How do I store dahlia tubers over winter in South Africa?
South Africa's winters are generally mild enough that tubers can be left in the ground in frost-free areas. In colder regions, lift them after the foliage dies back, cure for 24–48 hours, and store in a cool, dark, dry location packed in vermiculite or dry newspaper. Check monthly and remove any tubers showing rot. Replant from August–September once frost risk has passed.
How many tubers can I expect from a seed-grown dahlia plant?
A healthy first-year seed-grown dahlia in good soil with adequate water and feeding can produce 6–10 tubers. This is comparable to a purchased tuber in its first season. By year two — when you're replanting those harvested tubers — you can expect even larger, more vigorous clumps.
Is it worth growing dahlias from seed rather than buying tubers?
It depends on your goals. If you want a specific variety, reliability, or earlier blooms, tubers are the better choice. If you want to grow a large number of plants affordably, enjoy the surprise of variability, or build a tuber collection from scratch, seeds are excellent value. Many experienced dahlia growers use both approaches simultaneously.
Can I save seeds from my own dahlias?
Yes, though it requires the plant to set seed after flowering rather than deadheading. Allow some spent flower heads to remain on the plant and dry fully. Harvest the seed heads when brown and papery, dry them indoors for 1–2 weeks, then extract and store seeds in a cool, dry location. Note that the seedlings will again be variable — not identical to the parent plant.