Few flowers can match the dahlia for sheer spectacle. From enormous dinnerplate dahlias to dainty pompon dahlias with neat round heads, the stunning blooms with their vivid colours and striking shapes add exotic appeal to any garden.
Flowering from mid‐summer until the first frosts, dahlias provide a fabulous and long‐lasting splash of colour in the border. These versatile plants are perfect for tropical‐style planting, but can also combine beautifully with traditional cottage garden plants.
Our Dahlia Growing Guide gives you all you need to know about sowing, planting and caring for dahlias.
Types of Dahlia
Dahlias come in a wide range of shapes and sizes, so there’s one to suit every garden. They are grouped into categories based on the shape of their flowers. The number of categories varies, but the list below shows the main dahlia types:
- Single‐flowered dahlias – These have a single row of petals around a central disc.
They are one of the best dahlia types for pollinator‐friendly gardens, as bees and other insects can easily reach the centres to gather nectar.
- Cactus dahlias have double flowers with narrow, outward‐curving petals that are rolled so that they form a tube the whole length of the petal. The narrow petals give the flowers a spiky look, hence the name ‘cactus dahlia’.
- Semi‐cactus dahlias are very similar to cactus dahlias, but their petals are only rolled for part of their length, so look broader than those of cactus dahlias.
- Pompon dahlias have small round heads made up of inward‐curving petals.
- Ball dahlias also have rounded or slightly flattened heads of petals, but are bigger than pompon dahlias.
- Waterlily dahlias have open, saucer‐shaped double flowers that resemble waterlilies.
- Anemone dahlias have a tuft of tubular petals at the centre, surrounded by an outer single or double ring of flatter petals.
- Decorative dahlias are fully double, with flattened broad petals that curve outwards (unlike the inward‐curving petals of ball dahlias). The size of the flowers ranges from small to very large.
- Collarette dahlias, as the name suggests, have a ‘collar’ of small petals around a central disc, surrounded by another outer ring of large petals.
- Fimbriata dahlias have petals that split at the tips, giving the flowers a frilly appearance.
- Star dahlias have a single ring of narrow, rolled petals around a central disc. The narrow petals give the flowers their characteristic star‐shape.
- Miscellaneous dahlias – This category includes all the dahlias that don’t fit into one of the above categories, including species dahlias, orchid dahlias, peony‐flowered dahlias, and the huge dinnerplate dahlias.
Where To Grow Dahlias
Dahlias need full sun and a fertile, moist but well drained soil. Prepare your soil before planting dahlias by digging in organic matter such as garden compost or well‐rotted farmyard manure. Dahlia tubers will rot in poorly drained soil, so if you garden on very heavy clay, it’s best to plant your dahlias in raised beds or pots where you can give them the well‐drained growing medium they need.
Originating from tropical areas of South America, dahlias are tender plants and need protection in British winters. In mild areas with well‐drained soil, the tubers may survive in the ground if given a good thick mulch. In cold areas, or in areas with clay soils, the tubers should be dug up in autumn and stored in a frost‐free place over winter for replanting in spring.
Growing Dahlias From Seed Or Tubers
Growing dahlias from seed is a good way to get a lot of plants relatively inexpensively. Most dahlia seeds are sold in mixed packs, so you won’t know exactly which cultivars you are getting, but they’re great for providing a splash of colour in pots and beds.
If you want to grow a specific dahlia cultivar, it’s best to grow it from a tuber.
How To Sow Dahlia Seeds
1. Fill a module tray with multipurpose compost.
2. Place a seed on the surface of the compost in each module and cover lightly with more compost.
3. Water the tray and place in a warm position at a temperature between 15‐20°C (59‐68°F). Keep the compost moist but not sodden.
4. When the seedlings have 6 leaves, pot them on into larger pots and grow on indoors until ready to plant out, after all risk of frost is over.
How To Plant Dahlia Tubers
1. To have dahlias ready to flower in summer, start the tubers off indoors in pots in mid‐spring (early April in the south of the UK, a few weeks later in the north).
2. Plant the tubers in individual pots filled with a good peat‐free multipurpose compost. Dahlia tubers often come in clusters with the remnants of last year’s flower stem at the top of the cluster. Plant the tuber or tuber cluster so that the tips of the tubers are just below the surface of the compost, with the stem above ground.
3. Water the pots well and allow them to drain. Place them somewhere bright, cool but frost free for a few weeks to allow them to shoot and put on leaves. Keep the compost just moist.
4. Before planting out dahlias, harden them off for a week or so by leaving the plants outside in their pots during the day and bringing them back inside at night.
How To Plant Dahlias
1. Plant dahlias into soil that has been enriched with organic garden compost or wellrotted farmyard manure. Water well after planting. Tall dahlias and those with large, heavy flowers will need staking, so put these stakes in when planting to avoid damaging the tubers later.
2. To produce bushy plants with lots of flowering side shoots, pinch out the main growing tip of each plant when the plant is around 20cm tall, cutting just above the top pair of leaves.
3. Feed plants fortnightly with a high potash feed like tomato feed to encourage them to produce plenty of flowers, and water them in dry periods.
4. Deadhead faded flowers regularly to encourage more blooms. To tell the difference between a new bud and a spent flower, look at their shape. New buds are round with a slightly flattened end while spent flowerheads have a pointed end.
Tips On Overwintering Dahlias
Wait until after the first frosts have blackened the foliage, then cut back all the stems to just above ground level.
In mild areas, or areas with very well drained soil, tubers can be left in the ground, covered with a thick layer of dry mulch such as composted straw.
In cold areas, or if your soil is heavy clay, it’s best to lift tubers in autumn, otherwise they are likely to rot over winter.
How To Lift & Store Dahlia Tubers
1. Using a garden fork, dig gently around the edge of the rootball and lift the clumps of tubers out, taking care not to damage the tubers.
2. Shake off any excess soil.
3. Label the plants and place them in a frost‐free spot, hanging them upside down for a few days to allow any liquid in the stems to drain out.
4. Once this has been done, place the tubers right way up in a tray and cover them with sand or compost. If you only have one or two tubers, pot them up into individual pots.
5. Moisten the sand or compost very slightly. Leave the tray or pots in a cool, wellventilated place over winter. Check occasionally and remove any tubers that show signs of rotting.
Pests & Diseases
Dahlias are very prone to being attacked by slugs and snails. Protect the young plants with slug deterrents such as slug pellets, nematodes, or copper tape around pots.
Aphids can be a problem, especially on new growth. Wipe off infestations before they take hold, or spray with an insecticide. Don’t spray pesticides when plants are in flower, as this can harm bees.