Updated/Fact-Chacked on April 10, 2022 by John
Dahlias are known for their colourful flowers and long flowering seasons. Dahlia flowers have hundreds of different shapes and sizes which make them unique; it’s estimated that 42 dahlia species exist, and hundreds of different hybrids. Your garden will definitely be enhanced if you add these flowers to your borders, our guide will give you the best chance to make them thrive.
Dahlias grow in damp, cooler climates and flower from July to the end of October, perfect if you are looking to add some autumn colour to your borders when everything else is dying off. Dahlias also make great cutting flowers, so bring some stems indoors for vases when the plant is in full bloom. Dahlias are not suited to areas with hotter climates, for our readers outside the UK.
When choosing a dahlia variety you want to plant, consider the plant’s colour and height so you can plant against a well-matched companion. Dahlias can also be used to add vertical interest to the back of a sunny border.
Below is a list of some of the common dahlia varieties available and their appearances in bloom.
Cactus and Semi Cactus Dahlia
These types have fully double blooms with thin and long pointed petals, giving them a fantastic mesmerizing, spiky appearance. These types of dahlia are very pleasing in the eyes. They use their star-shaped petals to help withstand wet weather; rain runs off the petals, unlike some dahlias that will droop under the weight of rain. They are also more resistant to strong winds, ideal if you live near a wind-battered coastline like myself. Examples are Dohris Day, Frigoulet, and Weston Miss.
Single dahlias have single blooms and the petals can be round or pointed. The disc petals can have up to three rows of yellow colour or orange florets, and the blooms can be over five centimetres in length. Butterflies and other pollinating species are attracted to these flowers so these are absolutely a treat for them – unlike most dahlias are not great for pollinators. Examples of these plants are Joe Swift and Bishop of Yours.
These dahlias are broad and have two blooms. Unlike other varieties, the central disc of this type is hidden and the petals are usually curved. Because of their decorative characteristics, they are often used in exhibits and house decoration. Examples are David Howard, Art Deco, Leopold Chloe, and Arabian Night.
You can also get amazing looking tri-colour dahlias like the kogane fubuki dahlia with a huge 25cm head. The kogane fubuki dahlia can also produce 20-30 flowers in a season from a single tuber, all with a rich blend of yellow and pink petals.
Pompom and Ball Dahlias
These dahlias are like pompoms just as their name suggests. The petals are curved inward which creates round-shaped flowers that are five cm long. Ball dahlias, on the other hand, are larger with a little flattened top. The petals are arranged in a spiral pattern. These types are best as container displays. Examples are Franz Kafkha, Moor Place, Plum Surprise, and Minley Carol.
These types of dahlias have a single ray of petals around the disc that are mostly open in the centre. The petals of orchid dahlias are lesser than the other varieties. Examples are Bishop of Aukland, Bishop of Oxford, and Bishop of Llandaf.
Guide to Growing Dahlias
You can grow dahlias in three main ways: Buying a plant from a nursery in the summer, growing from tubers in spring or by taking basal cutting from an existing plant.
Growing dahlias from tubers
You can buy dahlia tubers from garden centres or online during spring and grow in a greenhouse until May when there is no chance of frost. Dahlia tubers can be placed in shallow trays or pots and lightly covered with soil and watered. Within 4-5 weeks you will see shoots starting to grow and a plant develops.
Plant out after acclimatising (Put in day/bring in at night) in late May/early June, depending on where you live in the UK.
After they’ve bloomed (end November), pick the best and store the tubers for next year’s planting. Keep them in a dry place, like a garden shed, with no sunlight – any moisture will just make them rot.
Dahlias need full sunlight to have increased flower blooms – 5 hours of sunlight per day is ideal. You must put them in an area where they can reach direct sunlight and preferably in a sheltered spot away from strong winds.
Since Dahlias are summer plants, they require good, well-drained soil with high acidity. Organic fertilizer can also help. To prepare the soil before planting and aid drainage, dig 2 inches deeper than the required depth. Dahlias grow swiftly if they are planted in a well-prepared soil bed. The holes and spacing vary on the variety of dahlia plants you are growing.
Certain taller dahlia varieties may require the assistance of staking, insert some strong stakes around the plant and tie some of the main shoots to the stakes as the plant grows. You may require multiple stakes around the plant as dahlias can grow quite bushy.
To keep the flowers in continual bloom in the flowering months, deadhead regularly – soon as you deadhead them, you see new flowers instantly bloom over coming days.
Dahlias are quick eaters of fertilizers which makes them have massive roots. As a result, you’ll have increased flower blooms which also affects the blooming next season. The majority agree that dahlias bloom in rich, nutritious soil with plenty of organic material.
Dahlias flourish when they are being watered consistently but the soil must be kept dry. It is suggested that you use a container with a good draining ability. Drip irrigation is also useful since it keeps the leaves dry while directing hydration to the roots. When this is neglected, expect the roots to deteriorate.
Dahlia and Pests
Slugs and snails will devour a younger dahlia plant. I planted two out this summer, one in a border and one in a container. The dahlia in my border got completely devoured – I still might be able to save the tuber over winter and replant next spring, all is not lost.
Make sure you project newly planted dahlias with some form of natural slug and snail protector.
Growing dahlias FAQs
Do dahlias come back every year?
Yes they will if you don’t live in an area with cold winters, otherwise dig up the tubers, store and replant
Where do dahlias grow best?
Sunny positions south-facing borders in soil with good drainage
How long do dahlias take to grow?
Tubers can take 5-8 weeks to sprout and produce foliage
Do dahlias multiply?
Dahlia tubers will multiply each year if left in warm conditions, this is unlikely in the UK
Can dahlias grow in pots?
Yes, dahlias can thrive in pots, it’s easier to keep them at optimum conditions and they will generally produce more flowers.
Should I soak dahlia tubers before planting?
Soaking them in warm water for 1-2 hours is advised to help the hydrate for growing
How can I make dahlias grow faster?
Before placing the tubers in your hole, add some compost to provide additional nutrients when the root starts to sprout.
Mary shares a passion for gardening with her husband John, though she is more focused on growing veg on their allotment at St. Margaret’s Allotments, Durham. Mary also works in the lawn care industry and manages the lawns for the Durham University campus.