There is no flower quite like a dahlia. From the smallest single-petalled pompom to the largest dinner-plate bloom, dahlias have a drama and a generosity that few other garden plants can match. They flower prolifically from midsummer through to autumn, producing an abundance of blooms in a colour range that spans almost the entire spectrum — from the palest blush to the deepest burgundy, from bright sunshine yellow to rich violet purple.
They are also, despite their spectacular appearance, surprisingly achievable for the home gardener. Grow them from seed, give them sun and water, and they will reward you with months of blooms that are as beautiful in a vase as they are in the garden. In this complete guide, we cover everything you need to know to grow dahlias successfully in South African conditions — from sowing seed through to cutting, storing, and overwintering.
About Dahlias
Dahlias (Dahlia variabilis) are tender perennials native to Mexico and Central America, where they grow in warm, well-drained conditions at altitude. This origin gives us important clues about how to grow them well: they love warmth and sun, need excellent drainage, and are frost-sensitive — which in most parts of South Africa means they can be grown as summer annuals or overwintered as tubers in cooler regions.
Our Dahlia Seeds are heirloom, non-GMO seeds selected for vigour, colour range, and performance in South African conditions. Growing dahlias from seed (rather than tubers) is a more economical way to start, and it produces a wonderful diversity of flower forms and colours — each seedling is slightly different, making your dahlia garden genuinely unique.
When to Sow Dahlia Seeds in South Africa
Dahlias are warm-season plants that need frost-free conditions to thrive. Unlike many annuals, they benefit from being started indoors before transplanting, as they need a longer growing season to reach flowering size from seed.
- Highveld (Gauteng, Mpumalanga, Free State): Start seeds indoors in August to September, 6–8 weeks before the last frost. Transplant outdoors from October onwards.
- Western Cape: Start seeds indoors in September to October. Transplant from November as temperatures warm.
- KwaZulu-Natal and coastal regions: Start seeds from August. The longer warm season allows earlier planting and a more extended flowering period.
- Limpopo and Northern Cape: Start seeds in August to September for transplanting in October.
From seed, dahlias typically flower in 90–120 days — so seeds started in August or September will be flowering by December or January, giving you blooms through the summer and into autumn.
Sowing Dahlia Seeds
Starting Indoors
Dahlia seeds are best started indoors in seed trays or small pots filled with a quality seedling mix. Sow seeds lightly, about 3–5mm deep, and keep the growing medium consistently moist but not waterlogged. Place in a warm, bright spot — a sunny windowsill or a warm greenhouse works well. Germination typically occurs within 7–14 days at temperatures of 18–22°C.
Once seedlings have two sets of true leaves, prick out into individual 10cm pots and grow on in a bright, warm spot until they're ready to transplant outdoors.
Hardening Off
Before transplanting outdoors, harden off seedlings over 7–10 days by placing them outside in a sheltered spot for increasing periods each day. This acclimatises them to outdoor conditions — wind, temperature fluctuation, and direct sun — and reduces transplant shock significantly.
Planting Out
Choosing a Site
Dahlias need full sun — at least 6–8 hours of direct sunlight daily. In partial shade, they become leggy, produce fewer flowers, and are more susceptible to disease. Choose your sunniest bed, ideally with some shelter from strong winds, which can damage tall stems and large flower heads.
Soil Preparation
Dahlias thrive in fertile, well-drained soil with a slightly acidic to neutral pH (6.0–7.0). Prepare the bed thoroughly, incorporating generous amounts of well-rotted compost. Good drainage is essential — dahlias will not tolerate waterlogged roots and are prone to tuber rot in wet conditions. In heavy clay soils, raise the bed or incorporate coarse sand to improve drainage.
Spacing & Planting
Space dahlia seedlings 30–45cm apart for smaller varieties, and up to 60–90cm for larger dinner-plate types. Plant at the same depth they were growing in their pots. Water well after planting and keep consistently moist until established.
Staking
Most dahlia varieties need staking — they grow 60–120cm tall and their large flower heads make them top-heavy, particularly in wind. Insert stakes at planting time (to avoid damaging tubers later) and tie stems loosely as they grow. Bamboo canes, metal stakes, or a grid of horizontal netting all work well. Don't wait until the plant needs support — stake early and the plant will grow into the support naturally.
Watering & Feeding
Watering
Consistent moisture is important for dahlias, particularly during flowering. Water deeply and regularly, allowing the soil to dry slightly between waterings. Avoid overhead watering, which can promote fungal disease on the dense foliage. A drip system or careful hand-watering at the base of the plant is ideal.
Feeding
Dahlias are hungry plants that respond well to regular feeding. Once plants are established and beginning to bud, feed every two weeks with a low-nitrogen, high-potassium liquid fertiliser (a tomato feed works well). This promotes flowering rather than leafy growth. Avoid high-nitrogen feeds, which produce lush foliage but fewer flowers.
Pinching & Disbudding
Pinching Out
When seedlings are 30–40cm tall and have 3–4 pairs of leaves, pinch out the growing tip just above the top pair of leaves. This encourages the plant to branch from the base, producing multiple stems and far more flowers than a single-stemmed plant would. It feels counterintuitive, but it makes a dramatic difference to the final plant.
Disbudding (Optional)
For the largest possible individual blooms — particularly on dinner-plate varieties — disbud by removing the two smaller buds that appear alongside the central bud on each stem. This directs all the plant's energy into the central flower, producing a single, spectacular bloom. For a more natural, abundant display with many smaller flowers, skip disbudding entirely.
Dahlias as Cut Flowers
Dahlias are among the most spectacular cut flowers you can grow. Cut stems in the morning or evening (never in the heat of the day), when flowers are just fully open. Use sharp, clean secateurs and cut at an angle. Place immediately in deep, cool water and keep in a cool spot for a few hours before arranging — this conditioning step significantly extends vase life.
In a vase, dahlias last 5–8 days with proper care. Change the water every two days and recut stems at an angle each time. They look spectacular on their own in a large vase, or combined with cosmos, sunflowers, and sweet peas for a full summer arrangement.
The more you cut, the more the plant produces — regular cutting is the single most effective way to extend the flowering season. Our posts on growing cosmos and growing sunflowers cover two more excellent cut flowers to grow alongside your dahlias for a full season of blooms.
Pests & Problems
- Aphids: Common on new growth. Treat with neem oil or a strong jet of water. Encourage ladybirds and lacewings, which are natural predators.
- Earwigs: Can damage petals overnight. Set traps (rolled newspaper or a pot filled with straw) near plants and dispose of earwigs in the morning.
- Powdery mildew: Common in warm, dry conditions with poor airflow. Ensure good spacing, avoid overhead watering, and treat with dilute neem oil at the first sign.
- Slugs & snails: A particular problem with young seedlings. Use copper tape, eggshells, or iron phosphate pellets around plants.
- Tuber rot: Caused by waterlogged soil. Ensure excellent drainage and avoid overwatering.
Overwintering Dahlia Tubers
In frost-free regions of South Africa (most coastal areas and the warmer parts of KwaZulu-Natal and Limpopo), dahlias can be left in the ground over winter and will regrow from their tubers the following spring. In frost-prone areas (the Highveld, parts of the Western Cape), tubers need to be lifted and stored.
After the first frost blackens the foliage, cut stems back to 15cm and carefully dig up the tuber clumps with a fork. Shake off excess soil, allow to dry for a few days in a warm, airy spot, then store in a cool, dry, frost-free location (a garage or shed works well) in boxes of dry sand, vermiculite, or newspaper. Check periodically through winter and discard any that show signs of rot. Replant in spring once the risk of frost has passed.
Dahlias & Pollinators
Single and semi-double dahlia varieties — where the centre of the flower is open and accessible — are excellent pollinator plants, attracting bees, butterflies, and hoverflies. Our Dahlia Seeds include varieties with open centres that are particularly valuable for pollinators. Pair with cosmos and sweet peas for a pollinator garden that flowers from spring through to autumn.
For more on creating a pollinator-friendly garden, our post on growing sweet peas and our home fragrance guide — which covers bringing garden botanicals indoors — are both worth reading.
Shop Dahlia Seeds
Ready to grow your own? Our Dahlia Seeds are heirloom, non-GMO seeds selected for South African conditions — vigorous, colourful, and productive. Sow them this spring and you'll have a garden full of spectacular blooms from midsummer through to autumn, with armfuls of cut flowers for the house and a display that will stop visitors in their tracks.
Dahlias are one of those flowers that reward the gardener who pays attention. Stake them, feed them, cut them generously, and they will give you one of the most spectacular flowering seasons your garden has ever seen.