7 Easy Steps to Grow Dahlias

Last Updated on 19/11/2022 by Barney

Growing Dahlias is easier than you think

If you’re looking for an easy-to-grow flower with a long flowering season then growing Dahlias should be at the top of your list. Flowering from mid-summer right up until the first autumn frosts I cannot think of a better value for money plant.

Dahlias come in a variety of shapes and sizes, making them perfect for any garden. In this guide, we will teach you everything you need to know about growing dahlias. From planting to pruning, we have you covered. Anyone can grow dahlias!

I’ll be completely honest; I was never that keen on them until now I always thought they were too flouncy with their showy blooms. However, years of growing them for clients and more recently becoming a Dahlia addict I am truly in love!

There are 1000s of varieties and a whole myriad of colours, shapes & tones that will draw you into the dark side, ‘dahlia-itis’ I call it.

So, without further ado continue reading for my easy steps to grow dahlias.

Growing Dahlias in the Flower Border

#1 Choosing & buying your Dahlias

The hardest part when growing dahlias is coming to terms with the fact that you just simply don’t have the space to plant them all.

My advice when choosing Dahlias is to start with flower form. Do you want a flower that is huge and flouncy or delicate and formal? Cut flowers for the vase or superb pollinators for bees & butterflies?

Dahlia varieties are placed into the following groups, Single flowered, Anemone, Pompom, Single orchid, Collarette, Cactus Dahlias, Waterlily, Semi cactus, Peony, Decorative & Miscellaneous. Further information on the classifications can be found at the Dahlia Society

Within these groups lies 1000s of hybrids. You can now see why choosing a variety (s) to grow is the hardest part!

There are small, 45cm high plants that are perfect for front of border planting & attractive displays in planters and tall, 1.2m varieties that look fabulous in large planters or back of border planting.

Dahlias can be bought as Dahlia tubers or ready potted plants.

Dahlia tubers are the underground storage organs of the plant (just think what a daffodil bulb is to a daffodil) and can be divided yearly to produce new (free) plants, more on that to follow below.

Tubers are typically available for purchase from garden centres & on-line suppliers in the spring. The advantage of buying on-line rather than  garden centres is the sheer variety available.

Pot grown Dahlia plants are available to purchase in Spring and Summer.

#2 Planting & Soil Preparation (borders & planters)

preparing soil with a fork for planting Dahlias
Soil prep is key for successful Dahlias

Plant Dahlia tubers in late Spring when the risk of frost has passed. Sometime towards the end of May is usually fine. However, if you have a greenhouse you can start the tubers off undercover in early Spring.

Once you have purchased your Dahlias you will need to find the best spot in the garden to plant them.

Dahlias love full sun and a rich soil. They will fail to flower if planted in a shaded position.

To grow Dahlias pick any place in the garden that receives a minimum of 6-8 hours of direct sunlight.

Planting in the ground

Once you have decided on the best location I recommend a sprinkling of organic fertiliser such as blood, fish & bone. This will get the tubers off to a great start by promoting a healthy root system. Healthy roots = strong plants.

Alternately (or do both) dig in some well rotted manure with a garden fork. This works great at providing nutrients, enhancing poor soil and holding onto moisture in the Summer.

Prepare the planting hole by digging to the depth of your tuber. The biggest mistake many newbies to Dahlias make is planting the tuber too deeply.

There should be a central stem on the tuber, this was the old above ground growth. Make sure that this central stem is slightly protruding above the soil surface.

It might not be apparent which way up to plant the tubers and your worry is that you plant the tubers upside down. Look out for the old cut stem and if that is not apparent then the tubers ‘eyes’. These are small nodules at the top of a tuber where the new shoots will sprout from.

Once you have that sorted simply backfill and give a good watering.

I have learnt from experience that now is a good time to place any plant supports, especially if growing large varieties. Staking & supporting them after they have become formed bushy plants, you run the risk of damaging the plants.

Planting in pots and planters

At a minimum you will need a pot 30cm in diameter by 40cm deep. If growing a large variety then a larger pot will be necessary.

Good drainage is important to grow Dahlias in pots as the tubers will rot if sitting in wet sodden compost. Ensure your pot has 2 – 3 drainage holes covered with crocks.

Fill a pot with a either a good quality peat free multipurpose potting compost or preferably a loam based compost such as John Innes No2 , leaving enough space for the tuber. I always mix in a granular slow-release fertiliser at this point.

As with planting in the ground, the ‘eyes’ on the tuber face upwards, this is where the new growth will appear. Another good indication of which way up the tuber should be is more often than not an old stem is visible.

Simply place the tuber into your pot, fill the remaining space up to and over the eyes with compost ensuring the compost is in contact with all of the tuber. A few taps of the planter should help with this.

Give a good drench of water after planting and put in place any necessary supports. I find the tomato – peony supports are best for keeping the larger varieties upright.

#3 Water Dahlias Less with Mulching

mulching flower bed with compost
Conserve water with a thick layer of mulch around Dahlias

Dahlias are thirsty plants and to grow Dahlias successfully they are going to enjoy a really good drink, especially in the hot summer months (don’t we all).

You can cut down on having to pop out every morning or evening to water, by applying a thick mulch around the base of the Dahlia.

A couple of inches of organic matter or well-rotted manure will really help in retaining moisture in the soil.

In pots where the compost will dry out quicker consider a mulch of slate chippings or gravel around the plant.

#4 Pinching Out (not to be missed)

Pinching out is an important step. Pinching out Dahlias produces bushier plants and more flowers than Dahlias that have not ‘pinched out’.

When your plants are about 45cm high, simply take a clean, sharp pair of secateurs and snip the main stem down to 2 or 3 sets of leaves.

Dahlia stems are hollow so perform this on a dry day. Perform this on a rainy day or when rain is forecasted and the risk is rain entering the hollow stems and rotting the plant away from the tuber.

It is also a good idea when pinching out to remove any leaves that are touching the ground. This creates better air circulation around the plant and removes the chance of slugs and ear wigs using them as a highway up to the good stuff.

When buying ready grown Dahlia plants this will not be necessary.

#5 Watering & Feeding

Dahlia plants need ample watering and feeding throughout the growing season to ensure healthy plants with masses of flowers.

One good watering every other day is normally fine except in the height of summer where you will want to water every day if you do not have a deep mulch around your plants.

To ensure a great display of flowers start feeding in July when the first flower buds appear until early September. Use something like Tomato right which is high in potassium. Apply every 2 weeks for best results.

#6 Deadheading

deadheading Dahlias with secateurs
Deadheading Dahlias keeps them flowering until the first frosts

Dahlias are fabulous at repeat flowering if you regularly deadhead.

When the booms start to fade and drop petals simply follow the stem down to a set of leaves and make the cut above with a sharp pair of secateurs.

#7 Winter Care

Being a tender perennial, once the first frosts have been Dahlias will look very sorry for themselves.

To overwinter dahlias there are a couple of options.

Option 1 – if planted in the ground apply a deep mulch of organic matter to protect the tubers from the cold.

Option 2 – if your soil tends to become waterlogged and / or you live in an area with prolonged cold snaps you should lift the tubers and store for next year.

To store them for winter simply cut all the old foliage back to the ground. Carefully dig the tubers with garden fork and store in pots or crates filled with dry compost or sharp sand .

The tubers are dormant and the pots or crates need to be stored in a dry, frost free place away harsh frosts or freezing temperatures. A garden shed, greenhouse or garage is perfect.

Dahlia Quick Questions & Answers

Do you soak dahlias before planting?
Whilst it is not essential to soak the Dahlia tubers before planting it does help in rehydrating the tuber and speeding up the process. A few hours in a bucket of water will do just fine.
When to plant dahlia tubers in pots or the ground.
Young plants will get severally damaged by a late frost, with this in mind plant tubers when the risk of this has passed. The end of May is a safe bet.
Tell me the best way to plant a Dahlia tuber?

Planting Dahlia tubers is done in the Spring, after the last frost has passed.

If planting in the ground get your Dahlias off to the best start and sprinkle some blood, fish & bone over the  planting area.

To plant, simply dig a planting hole that is twice the width of the tuber and about eight inches deep. Place the tuber in the hole so that the growing point is facing up and cover with soil. Water well and keep moist until new growth appears.

Once your dahlia has sprouted and has grown to about six inches tall, you will want to pinch off the centre growing point. This will encourage your dahlia to produce more branches and, as a result, more flowers!

You will also want to stake your dahlia plant as it grows taller. Large varieties can get top heavy with their huge blooms and have a tendency to topple over if not.

Storing Dahlias over Winter

Think about lifting and overwintering dahlias in a frost free place if you live in a particular cold area of the country where the temperatures plummet to below zero for days on end, .

See above here for details on how to overwinter properly.

How do you care for dahlias?

Dahlias benefit from being fed regularly. I like to use a good quality granular fertilizer such as bone meal or blood, fish and bone. Apply this around the base of the plant every few weeks from early summer onwards.

Alternately, a liquid feed can be given every week.

Stop feeding dahlias about six weeks before you plan to dig them up for storage over winter.

Water dahlias regularly, especially during dry spells. They will need more water when they are in flower and producing new growth.

Mulching around the base of the plant will help to keep the roots cool and moist during hot weather. This will also protect the tubers if leaving them in the ground for winter.

Dahlias are prodigious growers. They should be staked to prevent them from toppling. I like to use bamboo canes as they are lightweight and easy to maneuver. Place the cane next to the plant and tie it in using soft garden twine or raffia.

Do I need to deadhead Dahlias?

Dead heading Dahlias when the blooms have faded encourages the plant to produce more flowers. To deadhead, simply cut the flowering stem down to where it joins the main stem.

Check  weekly for any faded flowers that may be ready for removing. Keeping up with this routine will boost flowering well into Autumn.

Tell me the best place to plant Dahlias

Plant Dahlias where they will receive full & direct sunlight for at least six hours each day. They also need well-drained soil, so if your soil is heavy clay you may want to consider planting them in raised beds or improving the soil structure with horticultural grit and organic matter.

Dahlias do not like to be waterlogged, so ensure the bed is not in a low-lying area where water collects.

Dahlias are easy-going plants and will tolerate most soil types as long as it is well-drained. They will even grow in poor, stony soil

When should Dahlias be cut back

Once the first frosts have turned the foliage brown cut the Dahlia to ground level.

Leave a few cms of stalk remaining to identify which way up the Dahlia tubers need to be replanted the following year if overwintering the tubers.

Can I grow Dahlias in pots?

Absolutely, Dahlias make excellent pot plants. Just make sure the pots have drainage holes to allow excess water to escape and that you use a good quality, peat free potting mix or a loam based compost such as John Innes Number 2. .

You do not necessarily need big pots to grow Dahlias, there are plenty of bedding dahlias that only grow to around 45cm in height.

Water your dahlias regularly, especially during hot weather, and fertilise them every fortnight with a half-strength balanced liquid fertiliser such as tomato feed.

You will need to repot your dahlias every year into fresh potting mix and a slightly larger pot. This will ensure they continue to grow well and flower abundantly.

Dahlias growing in pots are also more susceptible to wind damage. Pick a sheltered spot to place them, Dahlias are susceptible to wind damage.

If you live in a particularly windy area or are growing tall varieties it is worth staking your dahlias to prevent them from blowing over.

You can do this by inserting a bamboo cane into the pot and tying the stem of the plant to it with some garden twine. Tall varieties will also need support if they are growing in borders.

Use a tomato cage or insert some bamboo canes around the plant and tie them together at the top with garden twine to create a support.

When is the best time to plant Dahlias?
he best month to plant dahlias is late May (or when the risk of frost has passed)
Can you leave Dahlia tubers in the ground over winter?

If you live in a area of the UK where the ground freezes for days on end or prone to waterlogging then I recommend lifting & storing for the winter.

Apply a good mulch and eave them in the ground if neither of these are a concern.

How Can I keep Dahlias flowering longer?

Regular deadheading and feeding every fortnight your Dahlias should flower right up until the first frosts.

Can I grow Dahlias from seed?

It is easy to grow dahlias from seed with a module seed tray and a propagator lid and a sunny window sill.

Sow 2 seeds per module on the compost surface and lightly cover with some additional compost. Water, cover and place onto a warm, sunny windowsill.

Growing Dahlia plants from seed is cheaper than buying tubers however Dahlia seeds are only supplied as mixed varieties. If you do not mind a riot of colour then this isn’t a problem.

Dahlia seed can be harvested from plants and kept in an envelope over winter for sowing the following spring.

What can I do with a poor flowering Dahlia?

Dahlias need full sun ad regular watering. Additionally a twice monthly feed with Tomatorite will ensure a great display of Dahlia flowers

It’s a Wrap from Me

Dahlias are wonderful plants to grow, and they’re easy too! If you haven’t tried growing dahlias before, now is the time. They make great additions to any garden, and with a little bit of care, you can enjoy their beautiful blooms for many seasons. So go on, grow some dahlias! You won’t regret it.