How to Grow Dahlias

Dahlias are one of the most rewarding flowers to grow, bursting into vibrant blooms from midsummer until the first frost. Whether you're growing them for your garden or as cut flowers, these stunning plants add colour and charm to any space. And the best part? With a little care, you can keep your dahlia tubers going year after year. One of the questions we get asked the most at The Gardeners Co. is how to grow and care for dahlias, so here’s a bit of a guide on how to grow, split, and store dahlia tubers for a continuous display of gorgeous flowers, with tips from our Head Gardener Shan, who for a short time ran a dahlia farm!

Planting Dahlias: When and How

Dahlias are normally grown from tubers, which are like underground storage organs. Unlike seeds, tubers will grow into identical copies of the parent plant, ensuring consistent colours and shapes. Be warned though, some suppliers do mix up their tubers and Shan has, on more than one occasion, had a complete surprise when a dahlia blooms with the colours and shapes. You can also grow a limited number of dahlias from seed, and they're easy to get started if you've not got your eye on a specific variety!

When to Plant

Here in the South West, the climate is relatively mild, but spring frosts can still pose a risk.

Starting indoors: You can begin your tubers indoors in pots in early spring (March to April) and move them outside once the risk of frost has passed.
Planting outside: From late April to May, when the soil has warmed up to around 15°C, you can safely plant them directly in the ground.

How to Plant

Pick the perfect spot – Dahlias love sunlight! Choose a location that gets at least 6-8 hours of direct sun each day.
Prepare the soil – Dahlias thrive in well-draining, fertile soil. They really benefit from a few handfuls of well-rotted manure when planting, so it’s worthwhile trying to get hold of some if you can.
Plant the tubers – Dig a hole around 4-6 inches (10-15 cm) deep. Lay the tuber horizontally with the ‘eye’ (growth point) facing upwards. Cover with soil, but don’t water until shoots appear to prevent rot.
Provide support – Taller varieties need staking, so pop in a stake at planting time to avoid damaging roots later.

Growing Dahlias from Seed

While we usually grow from tubers, Dahlias can also be started from seed, offering a cost-effective way to grow new varieties.

Sow indoors – Start seeds indoors in trays or small pots in March or April, using a light, free-draining compost.
Keep warm – Maintain a temperature of around 18-20°C for successful germination.
Transplant seedlings – Once they develop their first set of true leaves, move them into individual pots.
Harden off – Before planting outside, gradually acclimate the young plants to outdoor conditions by placing them outside during the day for a week.
Plant out – In late May or early June, when all risk of frost has passed, plant the seedlings in the garden, spacing them around 30cm apart.

Growing dahlias from seed won’t guarantee exact replicas of the parent plant, but it’s a fun way to discover unique new blooms!

Caring for Your Dahlias

Once your dahlias start growing, they’ll need some TLC to keep them blooming beautifully.

Watering: During dry spells, water deeply twice a week. Avoid overwatering to prevent tuber rot.
Feeding: Apply a balanced, low-nitrogen fertiliser every few weeks to promote flowers rather than leafy growth. We recommend a tomato feed - something like the Envii Maximato is organic and high in potassium to help fruit and flower development.
Pinching: When the plants reach about 20cm tall, pinch out the growing tip to encourage bushier growth and more blooms. This might seem scary, but we promise you it'll do your plants a world of good to make them stronger, bushier and producing more blooms.
Deadheading: Regularly remove spent flowers to keep the plant producing more.

Keeping them Going Year After Year: How to Split Dahlia Tubers

Dividing dahlia tubers is a great way to multiply your plants and keep them healthy. This is best done in late winter or early spring before planting.

Lift the tubers – In autumn, after the first frost blackens the foliage, carefully dig up the tubers with a garden fork.
Clean and dry – Gently shake off excess soil and let them dry for a day in a frost-free area.
Check for eyes – Each tuber must have at least one ‘eye’ (growth bud) to grow into a new plant. The eyes are usually near the old stem.
Separate the tubers – Using a clean, sharp knife, cut tubers apart, making sure each division has an eye and a section of the main crown.
Store or plant – Either store them for the winter or plant them straight away if it’s springtime.

How to Store Dahlia Tubers For the Winter

Prolonged wet weather can cause tubers to rot if left in the ground. Unless your soil is free draining, it’s probably safest to dig them out to store until the spring.

Dry them out – After lifting the tubers, leave them to dry for a day in a well-ventilated place.
Remove excess soil – Brush off any loose dirt but avoid washing them, as excess moisture can cause rot.
Choose a storage method:

Wrap them individually in newspaper.
Pack them in dry sand, peat moss, or sawdust.
Store them in breathable paper bags or cardboard boxes.

Keep them cool and dark – Store in a frost-free place, such as a basement, garage, or shed, at around 4-10°C.
Check occasionally – Have a look every once in a while and remove any that show signs of rot or shrivelling.

Common Dahlia Growing Problems & Solutions

Slugs and snails – A damp climate can encourage slugs. Protect young shoots if you can.
Aphids – Spray with a mild soapy water solution or introduce beneficial insects like ladybirds.
Powdery mildew – Avoid overhead watering and ensure good airflow around the plants.
Weak stems – Stake taller varieties early and avoid excessive nitrogen fertilisers.

Why Grow Dahlias?

Dahlias offer so much more than just beautiful blooms. They’re:

Incredible cut flowers – They last up to a week in a vase.
Great for pollinators – Bees and butterflies love them. The open-facing blooms in particular!
Available in countless varieties – From tiny pom-poms to dinner-plate-sized blossoms, there’s a dahlia for everyone.
Easy to propagate – Split tubers each year and share them with friends and fellow gardeners.

Dahlias are an absolute delight and it’s easy to see why they’re so popular in our groups and Lady Gardeners’ sessions. With proper planting, care, and overwintering, these stunning blooms will reward you with months of flowers. Just remember to plant them in a sunny spot, give them a little care, and store the tubers safely over winter for an even better display next year. Enjoy!

For more plant growing tips and inspiration, make sure to follow us at @thegardenerscocic!

Back to blog