Growing Dahlias Rhs – Your Ultimate Guide To Show-Stopping Blooms

ByRimon Chowdhury Updated on

Have you ever scrolled through photos of gardens bursting with the spectacular, geometric blooms of dahlias and thought, “I wish I could grow those, but they look so complicated”? It’s a common feeling among gardeners when faced with such floral perfection.

I’m here to tell you that you absolutely can, and it’s easier than you think. With a little guidance based on trusted Royal Horticultural Society (RHS) principles, you can cultivate these garden divas with complete confidence. Don’t worry—these flowers are perfect for beginners!

This complete guide on growing dahlias rhs style will walk you through every single step, from choosing the right tubers to storing them for next year’s magnificent display. We’ll cover planting, feeding, staking, and even how to tackle common pests sustainably. Get ready to fill your garden and vases with breathtaking flowers.

Why Dahlias Deserve a Spot in Your Garden (and the RHS Seal of Approval)

Before we dig in, let’s talk about why these flowers are so special. The sheer variety is mind-boggling, with forms ranging from perfect, tight pompons to giant, spiky ‘cactus’ types and elegant ‘waterlily’ blooms. They are, without a doubt, the stars of the late summer and autumn garden.

The benefits of growing dahlias rhs style go beyond just beauty:

  • Endless Flowers: The more you cut them, the more they bloom! They provide a continuous supply of flowers for your home from mid-summer right up until the first frosts.
  • Pollinator Paradise: Simple, open-faced varieties like the ‘Bishops’ series are magnets for bees and butterflies, making them a fantastic choice for an eco-friendly growing dahlias rhs garden.
  • Incredible Variety: With thousands of cultivars, there is a dahlia for every garden size, colour scheme, and personal taste. Many of the best have received the prestigious RHS Award of Garden Merit (AGM).
  • A Rewarding Process: There is a unique satisfaction in planting a strange-looking tuber in spring and watching it transform into a magnificent, flower-producing plant.

Getting Started: Choosing and Preparing Your Dahlia Tubers

Your journey to incredible blooms begins with a healthy tuber. A dahlia tuber looks a bit like a cluster of small, knobbly sweet potatoes. Think of it as the plant’s underground storage unit, packed with all the energy it needs to get started.

Where to Buy and What to Look For

You can buy tubers from late winter onwards from garden centres, nurseries, and online specialists. When choosing, look for a firm, plump cluster. Avoid any that are shrivelled, soft, or showing signs of rot.

Crucially, you need to see an ‘eye’ or a small shoot emerging from the central crown where the old stem was. This is where the new growth will come from. No eye means no plant, so this is a non-negotiable feature!

Waking Up Your Tubers

If you buy your tubers early in the year, you can give them a head start indoors. This is one of the most important growing dahlias rhs tips for getting earlier flowers.

  1. Find a Pot: Choose a pot that is just a little bigger than the tuber cluster. A 2-3 litre pot is usually perfect.
  2. Potting Medium: Fill the pot with a good quality, peat-free multi-purpose compost.
  3. Planting: Place the tuber inside with the old stem pointing upwards, and cover it with compost so the crown is just below the surface.
  4. Water Lightly: Give it a small amount of water to settle the compost, but don’t soak it. Overwatering at this stage is a leading cause of tuber rot.
  5. Location, Location: Place the pot in a bright, frost-free place like a greenhouse, conservatory, or a sunny windowsill. Growth should appear within a few weeks.
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The Complete Growing Dahlias RHS Guide: Planting for Success

Whether you’ve started your tubers indoors or are planting them straight into the garden, timing and preparation are everything. This is the core of how to growing dahlias rhs style for a healthy, productive plant.

When to Plant Outside

Dahlias are tender and cannot tolerate frost. The golden rule is to wait until all risk of frost has passed in your area. For most of the UK, this is typically from mid-May to early June.

If you’ve started your plants indoors, make sure you ‘harden them off’ for a week or two before planting them in their final position. This simply means putting them outside during the day and bringing them back in at night to acclimatize them to outdoor conditions.

Preparing the Perfect Spot

Dahlias are sun-worshippers and hungry feeders. To get the best results, you need to give them what they want.

  • Sunlight: Choose a spot that gets at least 6-8 hours of direct sunlight a day.
  • Soil: They need fertile, well-drained soil. Before planting, dig in plenty of well-rotted organic matter, like garden compost or manure. This improves soil structure and provides essential nutrients.
  • Spacing: Give them room to breathe! Spacing depends on the final size of the variety, but a good rule of thumb is around 60cm (2ft) apart.

How to Plant Your Dahlias

Dig a hole that is roughly 15cm (6in) deep. If you are planting a dormant tuber, place it in the hole with the eye pointing up. If you’re planting a young plant you started indoors, plant it to the same depth it was in its pot.

A pro tip is to put your support stake in now, right next to the tuber. Pushing a stake in later risks spearing the precious tuber cluster. Once the tuber is in place, backfill the hole with soil, firm it gently, and give it a good watering.

Your Dahlia Care Guide: Nurturing Plants All Season Long

Once planted, your job is to keep your dahlias happy. This ongoing growing dahlias rhs care guide covers the simple, regular tasks that lead to a spectacular floral display.

Watering Wisely

Dahlias are thirsty plants, especially once they are in full growth and flowering. Water them deeply once or twice a week, more during very hot, dry spells. Aim the water at the base of the plant to avoid wetting the foliage, which can encourage fungal diseases.

Feeding for Flowers

To produce all those amazing flowers, dahlias need a lot of food. Start feeding them a few weeks after planting and continue until early autumn.

Use a liquid feed that is high in potash (potassium), which is the nutrient that promotes flowering. A high-potash tomato feed is absolutely perfect for the job. Feed them every two weeks, following the instructions on the bottle.

The ‘Pinching Out’ Technique

This sounds scary, but it’s the secret to a bushy plant with lots of flowers! When your dahlia plant is about 30cm (12in) tall and has several pairs of leaves, find the main growing tip at the very top and simply pinch it out with your fingers.

This encourages the plant to produce side shoots from the leaf joints below. Each of these side shoots will then go on to produce a flower, giving you a much fuller, more productive plant.

Common Problems with Growing Dahlias RHS (And Eco-Friendly Solutions)

Even with the best care, you might encounter a few challenges. Don’t panic! Here’s how to deal with the most common problems with growing dahlias rhs gardeners face, with a focus on sustainable methods.

Slugs and Snails

These are the number one enemy of young dahlia shoots. They can devour a new plant overnight.

  • Solutions: Go out at dusk with a torch and remove them by hand. Use wool pellet barriers around the base of plants or copper tape around pots. Encourage natural predators like birds, frogs, and hedgehogs into your garden.

Earwigs

Earwigs love to nibble on dahlia petals, creating ragged holes. They are a nuisance but rarely kill the plant.

  • Solutions: A classic RHS-endorsed trick is to create earwig traps. Loosely stuff a small pot with straw or shredded paper, turn it upside down, and place it on top of the plant’s stake. Earwigs will hide in it during the day. In the morning, you can empty the pot far away from your precious dahlias.
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Powdery Mildew

This is a fungal disease that appears as a white, dusty coating on the leaves, usually in late summer when nights are damp and days are warm.

  • Solutions: Ensure good air circulation by not overcrowding plants. Water at the base of the plant, not over the leaves. Remove and dispose of any affected leaves immediately to stop it from spreading.

The Grand Finale: Lifting and Storing Tubers for Winter

In most of the UK, dahlia tubers need to be lifted out of the ground and stored over winter to protect them from frost and wet, cold soil. This is one of the most vital growing dahlias rhs best practices.

Wait until the first hard frost has blackened the foliage. This signals to the tuber that it’s time to go dormant.

  1. Cut Down: Cut the stems down to about 15cm (6in) from the ground.
  2. Lift Carefully: Use a garden fork to gently lift the tuber cluster from the soil, being careful not to damage it.
  3. Clean and Dry: Remove as much soil as you can and turn the tuber upside down for a few days in a dry, frost-free place to allow any water to drain from the hollow stems.
  4. Store Safely: Place the dry tubers in a cardboard box or crate and surround them with a dry material like sand, sawdust, or vermiculite. Store them in a cool, dark, and frost-free place like a shed or garage until it’s time to start the process all over again next spring.

Frequently Asked Questions About Growing Dahlias RHS

Can I grow dahlias in pots?

Absolutely! Dwarf or bedding varieties are perfect for containers. Choose a large pot (at least 30cm in diameter) with good drainage holes and use a high-quality peat-free potting compost. Remember that pots dry out faster, so you’ll need to be diligent with watering and feeding.

Why are the leaves on my dahlia turning yellow?

Yellowing leaves can be a sign of a few things. Most commonly, it’s a nutrient deficiency, especially a lack of magnesium. It can also be caused by overwatering or underwatering. Check the soil moisture first, and if that’s fine, try a dose of Epsom salts (one tablespoon per gallon of water) to see if it greens up.

Do I have to ‘disbud’ my dahlias?

For most gardeners, no. Disbudding is a technique used by exhibitors to get one giant, perfect flower per stem by removing the smaller side buds. If you’re growing for garden display or cut flowers, it’s best to leave all the buds on to get the maximum number of blooms.

Your Dahlia Adventure Awaits

There you have it—your complete journey to growing dahlias, RHS-approved. From a humble tuber to a profusion of breathtaking blooms, the process is one of the most rewarding in all of gardening.

Don’t be intimidated by their glamorous reputation. By following these simple steps for planting, feeding, and care, you are setting yourself up for a summer and autumn filled with colour. You have the knowledge and the plan.

So go on, choose a variety that makes your heart sing, find a sunny spot, and get planting. Your garden (and your vases) will thank you for it!

Rimon Chowdhury
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