Dahlias

Dahlias are colourful flowering perennials that flourish from spring to autumn. They grow from tubers but can also be planted from pots in flower or as seedlings during spring and summer. These are long-lasting garden plants. When planting dahlias, ensure there is enough space for them to grow as they create striking displays, whether intertwined with other plants or mass-planted to enhance your garden.

Dahlias were introduced from Mexico in the late 18th century. Early dahlias had single flowers, but modern dahlias are known for their large, full blooms in vibrant colours including yellow, orange, red, brown, pink and white. Some are multi-coloured.

There are 29 classes for hybrid dahlias including single and many differently shaped doubles with flat, spiky, tubular or quill-shaped petals. Around 10 types of dahlias are regularly sold and seen in gardens including Single, Cactus, Pompon, Collarette and Waterlily.

Although known as big flowers, not all dahlia blooms are big. The Pompon group has small, perfect balls of flowers on stout stems, while there are also low-growing forms of dahlias ideal for pots or borders.

There is a variety to suit every location, from a couple of pots on a balcony or spread throughout a garden border. Check out your local hardware or garden centres for dahlias that suit your location. Try stopping at just one! There are also online specialty stores that will give you even more inspiration.

Growing conditions

Aspect Dahlias need a sheltered location and enjoy full sun with light afternoon shade (especially in hot climates). Easily damaged by wind, these flowers need shelter along with staking or a plant support to stop damage to the flowers and stems, which are brittle. Cover with shade cloth during hot temperatures to avoid plant and flower damage.

Soil Fertile, well-drained soil provide the best conditions for dahlia growth and flowering. Add your own compost, organic matter and/or Seasol Super Compost when preparing the soil and use Seasol Plant + Soil Booster when planting. Seasol Advanced Potting Mix is ideal for potted dahlias. Follow the directions on the back of the pack for guidelines on planting dahlias.

Climate Dahlias grow in most areas but prefer a warm, temperate climate. In cold and frosty areas they die down in autumn, so plant after the threat of frost has passed.

What to do in your garden in late summer including tips on summer flowering plants incluing dahlias, and the benefits of liquid feeding plants in February 2025
How to grow and look after dahlias for stunning pot or garden flower display ncluding soil, planting, and feeding

General care

Watering Drought tolerance is a feature of dahlias during dormancy, but once tubers begin to shoot, regular watering is needed to support foliage and flower growth. Keep the soil moist, but take care not to overwater, as this can cause tubers to rot. Check plants and water more often when plants are in hot, dry or exposed conditions or if they are growing in containers.

Where the soil is water repellent, apply Seasol Super Soil Wetter & Conditioner. Water with Seasol or Seasol GOLD regularly every two weeks to promote healthy growth and reduce stress from heat, drought, pests and diseases.

Feeding and mulching Dahlias are big feeders, so keep them growing and flowering throughout summer and autumn with a regular application of a granular fertiliser such as Seasol plus Nutrients Roses & Flowers or in a pot, try PowerFeed Controlled Release for Flowers, Fruit & Citrus. After buds appear, feed regularly with a liquid fertiliser every 10–14 days with PowerFeed PRO SERIES for Roses & Flowers.

Spread mulch such as lucerne, sugar cane or straw around dahlias to deter weed competition. Add well-rotted manure and Seasol Plant + Soil Booster to the mulch for extra nourishment and to improve the soil.

Pruning Regularly pick flowers and remove spent flowers, to keep plants in bloom. Take care to differentiate between buds (generally tight and round) and spent flowers, which have an elliptical point. At the end of autumn, as growth begins to die back, cut dahlias to ground level. Tubers are lifted in areas with very cold winters but in most areas can be left in the ground. Lift and divide every couple of years in spring to keep plants vigorous.

Watch for

  • Grasshoppers They are hard to manage but can be caught early in the day before they warm up and make great food for poultry.
  • Snails and slugs Manage them by conducting a regular snail hunt to discover small snails hiding in the foliage or around flowers. Also, try beer traps or barriers such as wood shavings or eggshells. Snails and slugs are active in the evening, especially after rain. Reapply traps and barriers after rain.
  • Earwigs can be caught in homemade traps made with screwed-up newspaper stuffed into an upturned pot on a stake near the plants. Empty the trap and kill any earwigs before replenishing the trap with more scrunched newspaper.
  • Powdery mildew In autumn, dahlia leaves may be attacked by powdery mildew. It is most obvious on dark-foliage varieties. Remove diseased leaves and apply an organic fungicide to control the disease. If the plants are nearing the end of their best growth, simply cut them back hard.