How to Grow Dahlias: Planting Tubers, Staking, Pinching and Winter Storage

How to grow dahlias from tubers is simple once you get the planting, staking, pinching and winter storage right, so you’ll plant after frost, stake tall varieties and lift or mulch the tubers.

Dahlias give weeks of colour from midsummer to the first frost, and a single tuber can produce dozens of flowers, so it’s worth getting the basics right. This guide shows how to plant tubers, support and pinch the plants, feed and water them, deal with slugs and earwigs, and keep tubers safe through winter. It’s general information, and your local extension service or the Royal Horticultural Society (RHS) can add advice for your climate.

It belongs to the Flower Gardening guides and works with Flower Bulbs for Year-Round Bloom, Cutting Garden and Flowers That Attract Pollinators.

How to grow dahlias at a glance

These are typical values. Local frost dates and soil change the timing, so check with your extension service or the RHS.

Choosing a site and soil for dahlias

Dahlias need at least 6 hours of sun and shelter from strong wind. Rich loam with compost suits them, and clay needs sand or grit to drain, because soggy clay causes tuber rot. Dig in a bucket of compost per square metre before planting. Mulch of 5 cm protects roots and reduces weeds and moisture loss, but keep it away from the stems because contact encourages rot. Tall varieties need a spot out of the wind, and a sunny border beside a fence or hedge of yew or box helps.

How to plant dahlia tubers step by step

1. Wait for warm soil. Plant after the last frost, when the soil has reached about 12°C. Tubers rot in cold, wet ground.
2. Dig a hole 10 to 15 cm deep. Add a handful of compost or grit at the base for drainage.
3. Set the tuber with the eye up. The crown, where last year’s stem was, should face the sky.
4. Insert the stake now. Push it in beside the tuber before you backfill, to avoid piercing it later.
5. Cover and label. Fill the hole, label the variety and water lightly. Heavy watering before shoots show can rot the tuber.
6. Protect from slugs. A ring of gravel or a beer trap helps while the first shoots appear.

How growing dahlias depends on sun, feed and water

Dahlia needs sun and rich loam, because clay holds water and causes tuber rot. Compost feeds dahlia and improves clay, sand drains heavy soil, and mulch protects the roots and reduces weeds. Potassium feeds blooms while high nitrogen feeds leaves at the cost of flowers, so choose a tomato-style feed. Deadheading boosts bloom for 8 to 10 weeks, and cosmos and zinnia respond the same way. Water deeply once or twice a week, about 10 litres per plant in dry spells.

Slugs damage young shoots, and a ring of gravel blocks them. Earwigs eat petals, so a pot of straw on a stake traps them, while aphid attracts ladybird and hoverfly that control it. Powdery mildew attacks dahlia in dry, crowded beds, so space plants and water at the base. Marigold repels whitefly and nasturtium draws aphid away from dahlia, and lavender and echinacea beside the border attract bee and hoverfly.

Dahlia tolerates heat, but hydrangea needs steady water and peony prefers a cooler root run. Tulip and daffodil finish earlier, so dahlia fills the gap in your border. Compost feeds rose and dahlia alike, and mulch protects the tubers and reduces weeds around hosta, while sunflower and zinnia suit the same sunny bed and sage tolerates the dry edge. You can plant tubers in 5 litre pots and move them out after frost.

Staking and pinching dahlias for more blooms

Tie the main stem loosely to the stake with soft ties every 30 cm of growth. When the plant is 30 cm tall with three sets of leaves, pinch out the growing tip just above the third set. The plant then branches, and you get more stems and more flowers. Skip pinching on exhibition varieties grown for a single giant bloom. Disbudding, which means removing the two small side buds beside the main bud, gives larger flowers on long stems for cutting.

• Tall dahlias: 1.2 to 1.5 m stake, tie every 30 cm.
• Bedding dahlias: usually no stake; pinch lightly.
• Dinnerplate types: stake and disbud for the biggest blooms.
• Cutting types: pinch, then cut flowers often, as described in Cutting Garden.

How to lift and store dahlia tubers for winter

1. Wait for frost. After the first frost blackens the leaves, cut stems to 10 cm.
2. Lift carefully. Use a fork 20 to 30 cm from the stem and lever the clump out.
3. Dry upside down. Leave the clump for a few days in a frost-free spot so the stem drains.
4. Pack in barely damp compost. Use boxes with compost or sawdust at 4 to 10°C.
5. Check monthly. Remove any soft or mouldy tubers and mist if tubers shrivel.
6. Divide in spring. Cut clumps so each piece has a tuber and an eye.

In mild climates with well-drained soil, you can leave tubers in the ground under a 10 cm mulch of bark or leaf mould. Wet clay kills them, so lift in heavy soil. A qualified local nursery or your extension service can say whether your winters are mild enough.

Choosing dahlia types for your garden

Open-centred single dahlias suit bees and hoverflies, while double types give more petals but less pollen. Choose by height first, then by colour, so your border keeps its layers.

Dahlia problems and fixes

If a plant looks wrong and none of these fit, send a photo to your local extension service or an RHS adviser. Don’t spray in full sun or while bees visit.

Common mistakes

• Planting too early. Cold, wet soil rots tubers before they sprout.
• Staking late. A stake pushed in later can spear the tuber.
• Overfeeding with nitrogen. You get leaves but few flowers.
• Skipping slug control. Young shoots vanish overnight.
• Storing tubers wet. Rot spreads fast in a damp box.

Next steps

Order tubers in late winter and plant after your last frost. For other summer and autumn colour see Flower Bulbs for Year-Round Bloom and Flowering Plants for Full Sun. To bring blooms indoors, read Cutting Garden, and to keep bees visiting, read Flowers That Attract Pollinators. The Flower Gardening guides link every step.