Dahlias

The dahlia, with its large, colourful, and cheerful blooms, might just be the summer flower. If you’re looking to brighten up your outdoor space this summer, planting dahlia bulbs is the perfect way to start. Dahlias come in all sorts, colours, and sizes. Discover your favourites in the webshop.

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When to plant dahlia bulbs?

Dahlias are summer bloomers, meaning they will surprise you with their vibrant flowers from summer to autumn. Dahlia bulbs should be planted in the ground just after the start of spring, once the risk of frost has passed. If you want to get a head start, you can plant the dahlia bulbs in pots and place them in a warm spot, such as a greenhouse or conservatory.

How to plant dahlia bulbs?

Dahlias thrive in fertile, well-drained soil and prefer locations with plenty of sunlight. However, a sheltered spot is ideal. As mentioned earlier, you can "pre-sprout" dahlias by placing them in a warm spot indoors or in a greenhouse to acclimatise them. From April or May onwards, they can be planted outdoors in open ground.

Tip: Plant the dahlia bulbs just beneath the soil surface and space them about 75 centimetres apart, depending on the variety. Be sure to water them adequately.

planting dahlia bulbs

How to plant dahlia bulbs in pots?

Dahlias are a fantastic choice for container gardening, bringing vibrant color from summer through autumn. Because of Ireland’s cool and damp conditions, a little extra care is needed to get them off to a strong start.

Best time to plant Dahlia bulbs

  • Indoors: Start tubers in March or April to get an early bloom.
  • Outdoors: Wait until late May or early June, when all risk of frost has passed.

What you’ll need

  • A sturdy pot – At least 30 cm wide and deep, with good drainage.
  • Quality compost – A mix of multipurpose compost and horticultural grit helps prevent waterlogging.
  • Healthy dahlia tubers 
  • Fertilizer
  • Support stakes – Tall varieties will need support as they grow.

Step-by-Step Guide

  1. Prepare the pot: Add gravel or broken pottery at the base to improve drainage. Fill the pot with a compost and grit mix, leaving space at the top.
  2. Planting the tubers: Position the tuber horizontally with the buds facing up. Cover it with about 5–7 cm (2–3 inches) of compost but don’t bury it too deep. Leave a small gap below the rim of the pot for watering.
  3. Watering & placement: Water gently to moisten the soil but avoid overwatering. Keep the pot in a bright, frost-free location (a greenhouse, conservatory, or sunny windowsill works well).
  4. Moving outdoors: Once frost is no longer a threat (mid to late May), start moving the pot outside gradually to harden off the plant.
  5. Feeding & maintenance: Once growth takes off, feed with a high-potassium fertilizer (like tomato feed) every two weeks. Pinch off early growth tips to encourage bushier plants and more flowers. If growing tall varieties, use stakes or a plant support ring to prevent flopping.
  6. Enjoy the Blooms: With proper care, dahlias will start flowering by July and continue until the first frost.

Overwintering Dahlias in Ireland

Since Irish winters are damp, leaving tubers in pots outdoors can cause them to rot. To keep them for next year: Once the foliage dies back, cut stems to about 10 cm. Move pots to a dry, frost-free place like a shed or garage. Alternatively, lift the tubers, dry them out, and store them in sawdust or sand until spring.