Dahlias are a diverse group of flowering plants with a whole range of flower shapes and colours! Dahlia plants are easy to grow, giving you late summer colour when many other plants are past their best. Whether you want flowers for cutting or flowers for a pot by your back door there will be a dahlia to suit most places! Single-flowered varieties will also attract bees. Read our guide to learn how to grow dahlias in your garden.
Dahlias perform best in a rich, fertile, well-drained soil in full sun. They are heavy feeders so before planting, dig in plenty of well-rotted manure or compost and top-dress with a general purpose fertiliser. Dahlias are half-hardy so will need protection from frosts.
Dahlias can be grown from seed, dormant tubers or planted as pot-grown plants. If growing dahlias from seed, sow them between February and April. If growing dahlias from tubers, plant them from April to May. Potted dahlias are planted out in May and June. Space taller varieties such as 'Badger Twinkle' about 60cm (24") apart, medium sized varieties such as 'Candy Eyes' 45cm (18") apart, and dwarf bedding varieties 30cm (12") apart.
When growing dahlia tubers, plant them directly in the ground from around mid-April. Don't worry about frosts as the soil will insulate them. Prepare a planting hole that is 10-15cm (4-6") deep, and wide enough to accommodate the dahlia tuber comfortably. Place the dahlia tuber inside with the 'eye' (where the tubers meet - often with remnants of last year's stems) facing upwards. Backfill with the remaining soil, gently firming as you go and water the tubers in thoroughly. Tubers can also be potted up in April and grown on in a greenhouse for a head-start; planting out after all risk of frost has passed.
Growing Dahlias in pots is a great way to brighten up your patio. Make sure you choose a container which is at least 30cm (12") in diameter and depth for optimum growth. Use multi-purpose compost and add a slow-release fertiliser for strong growth - dahlias enjoy rich fertile soil. Plant tubers 10cm deep as you would when planting in the ground.
Dahlias are frost-tender, so pot-grown plants should only be planted out after all risk of frost has passed in late May or June. Alternatively keep your dahlias in a greenhouse such as our Eezee Greenhouse. If you planted your dahlias in the ground and shoots emerge whilst frosts still threaten, cover them with horticultural fleece for protection.
Tall dahlias are prone to flopping over and are easily damaged by the wind. Some timely stakes inserted early in the season will prevent this happening! Insert stakes when planting your dahlias, either using bamboo canes (canes and string if grown in rows) or twiggy sticks for a more natural look. You can also use garden obelisks to support your growing dahlias, placing the obelisk directly over the dahlia plant. The supports may look untidy initially, but your dahlias will soon grow to cover them. When tying in your Dahlias make a figure of eight with the string to prevent the stems rubbing against the canes.
Pinching out dahlias once they reach 40cm (16") tall encourages branching and more flowers. Simply pinch off the growing shoot just above a set of leaves. Dahlias can be further pinched once side-shoots develop. For giant blooms however, it's best to only allow between three and five flower stems to develop.
Once flowers appear on your dahlia plants, feed them with a high potash liquid fertiliser, such as tomato feed every two weeks until early September. Feeding dahlias will encourage more flowers.
Dead-head dahlia flowers as they fade to encourage more blooms to be produced. Simply pinch or cut the flower stem back to a pair of leaves to keep the plant looking tidy.
Dahlia tubers will need lifting with a garden fork once the first frosts have blackened the foliage. They can be left in the ground in mild areas although the soil must be well-drained. If leaving dahlia tubers in the ground, cover them with a 10-15cm (4-6") layer of bark chips or compost. Once lifted, clean the tubers and trim off any fine roots. Cut the stems down to 15-20cm (6-8"). Place the tubers upside down for few weeks to dry off completely. Once dry, put your tubers into boxes or trays of dry sand, peat-free compost, vermiculite or coir fibre and store in a cool but frost-free place. It's a good idea to check your dahlia tubers regularly throughout the winter to look for signs of mildew or rotting. Cut out any affected areas with a clean sharp knife.
Single-flowered Dahlias such as 'Windmill Mixed' attract bees.
Look for the remnants of last year's stems to identify which way up to plant your dahlia tuber.
Pinching out the stem tips encourages branching and more flowers.
Lift dahlia tubers for the winter once the first frosts have blackened the foliage. Cut the stems to 15-20cm (6-8").
© 2017 Van Meuwen. All rights reserved. A division of BVG Group Ltd.