When, Where and How to Plant Your First Dahlias

Everything you need to know about getting started with Dahlias

By Hannah Miller at DIY Gardening

Dahlias are my favourite garden plant, and I’m so glad to see more varieties on sale in garden centres after a slight lull in their popularity a few years back.

Dahlias aren’t the easiest plant to grow, but I’m confident that if you follow our 8 pointers below, you’ll fall in love with this stunning garden perennial.

If you’ve never grown a Dahlia before, this guide is for you, and we’ll cover:

  • The different types of dahlia.
  • What to look out for on the tuber.
  • How to store them until the weather is warm enough to plant them outside.
  • Starting them early; the why, how and when.
  • The best location.
  • Early season tips top get your Dahlias off to a head start.

Here’s just six photos out of the hundreds I took this summer:

Red and white dahlia
Orange dahlias
Purple dahlia flower emerging from a bud
Smaller dahlia blooms on stems
Large yellow and orange dahlia bloom
Dahlia bloom next to measuring tape

Step 1: Choose From One of These Dahlias

Dahlias have been grown in Europe for over 200 years, and there are over 50,000 varieties, but most can be grouped into about a dozen categories.

The three most popular are:

Decorative Dahlias (shown above) – These are the most popular, and they include the famous “Dinnerplate” variety, which produces flowers up to a foot wide.

Pompon and Ball Dahlias – Most are slightly more compact, but some can grow over 10 inches. These blooms are ball-shaped and therefore popular in architectural gardens as they add shape and interest to borders and even pots. The petals are concave and blunted at the tip.

Cactus Dahlias (shown above) – These have long pointed petals that roll back at the edges, making them stand about against all other Dahlias. Semi-cactus varieties aren’t quite so pointy but are still striking.

The Gardening Chores website lists more varieties of Dahlias and photos for each, so check out their guide here.

Step 2: What To Look Out For

Dahlias grow from tubers that look like thin, long potatoes.

These multiply under the soil and can be lifted after the first frosts and split with each new tuber forming a new plant the following spring. However, there is one caveat; the tuber will only grow into a plant if it has an “eye” – a small dark spot near the neck of the tuber.

If the tuber doesn’t have an eye, it won’t produce a stem, and no plant will grow, so make sure any tubers you buy from your garden centre have an “eye”.

The tubers often look shrivelled and unhealthy if they’ve been out of the soil for any length of time, but this is perfectly normal, and most will bounce back into life once they’ve been planted in the garden. 

Just make sure none are overly soft or squidgy as they might be rotten or diseased.

Step 3: How to Store Dahlia Tubers Until They’re Ready For Planting

As Dahlia tubers are susceptible to frost, you’ll probably need to store them in a sheltered spot until spring, and all risk of frost has passed.

Whether you’ve dug up your own tubers or purchased them online or from a garden centre, the best way to store them is:

  • Get a cardboard box.
  • Fill it with an inch of compost.
  • Cut holes in the sides for ventilation.
  • Place the tubers inside, making sure they don’t touch each other.
  • Cover the tubers with compost.
  • Place the box in a shed, garage, porch cupboard or anywhere dark between 5° and 10°.

The tubers should be ready to plant out in the spring when all risk of frost has passed.

Step 4: Start Them Off in Pots

Not everyone needs to start them off in pots. If you live in milder parts of the country, you can probably just plant them directly into the garden after all risk of frost has passed, but if you live in the north and have shorter summers, giving them a headstart will reap the rewards later in the season.

First, check out this map as it will tell you the expected date for the last frost date for your area.

You can either wait until it’s safe to plant them in the garden or give them a headstart about 6 – 8 weeks before the last frost.

Here’s how:

Place the tubers into pots and fill them with compost; you can use smaller pots and cram them into each one; they will only be in there for a month or two.

Place the pots in a greenhouse, a conservatory, porch or other area sheltered from the frosts and keep them watered but not waterlogged.

By the time the temperature warms up and there’s no risk of frost, you should have Dahlias with at least a few inches of top growth, possibly much more, and they’ll be ready to transplant into the garden border or a large pot outside.

Step 5: How to Choose The Best Location For Your Dahlias

The best location for Dahlias is:

  • In a bright spot with light on all sides if possible.
  • Near a water source, the gardener will need to water the dahlia several times a week and daily in heatwave conditions.
  • In a spot where the dahlia has some space, as they dislike crowded borders.
  • In a sheltered spot away from winds as the stems of Dahlias are very fragile.
  • In well-drained soil as the tubers may rot if left in waterlogged ground.

Step 6: Early Season Tips

Follow these tips to get your Dahlias off to a great headstart:

Have a Slug Plan – These pests love Dahlias, and you’ll need to plan ahead as they can quickly get through the foliage, as you see from the image below:

Slugs damage to dahlia leaves

Slug damage to a young Dahlia. If left unchecked they will devour all the leaves and weaken or kill the plant.

Try these slug repellants and traps.

Stakes and Supports – Dahlia stems are prone to snapping during the wind, so you’ll need to buy some stakes and ties or, even better, some frames to support the plant throughout the growing season.

The best garden stakes and Dahlia frames can be found here.

Feed and Fertiliser – We’ve already published a guide to the best fertiliser for Dahlias. In short, avoid nitrogen-rich feeds as Dahlias are often top-heavy, and nitrogen can make the plant grow leggy.

Don’t Forget to Pinch Out – To encourage Dahlias to grow bushy rather than leggy, one should pinch out the centre of the stems early in the season; the best time is to wait until there are three sets of nodes on the stem.

Conclusion

Dahlias are beautiful late-summer perennials that produce plenty of often large and eye-catching blooms, but they are tender and require more love and care than your average plant.

I hope this guide gets you off to a good start and you enjoy growing Dahlias as much as I do.

More From Hannah Miller:

This guide to getting started with Dahlias was created by Hannah Miller and is part of our guide to growing plants and was last updated in November 2021.

You may also like our Ultimate Guide to Growing Dahlias.

Hannah is a keen amateur gardener, mother and a former NHS administrator.

She enjoys gardening as much as she cares about the environment and likes to share her knowledge with others.

Hannah is a keen photographer, and you’ll find hundreds of her photos throughout this site. She also contributes to our blog; check out her latest posts here.

Author Hannah Miller

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