Are Dahlias Perennials Or Not? Learn All About Them Here!

Already a pro when it comes to hydrangeas, roses and even aloe vera plants? Don’t stop now! Summer wouldn’t be the same without dahlias. Nobody can possibly resist their diversity of colours, styles and sizes. They make excellent cut flower plants, and their lovely bloom heads typically survive far into the autumn, extending the flowering season. It’s true! Their beautiful, brilliant flowers bloom from mid-summer to late autumn.

Purple dahliasHowever, this variety of shapes and colours is made up of tubers that must be cared for in order to return year after year, so the question is are dahlias perennials? Or are they simply biennial? Read on to find out more. 

What are perennials?

Perennials are typically plants that come back every year in the spring. Their bloom time is usually one season a year (spring, summer, or autumn). They can also live for a long period if grown in the right conditions, but don’t expect them to last forever.
Their lifespan varies, with some only living three to five years. Perennials also have a wide range of care and maintenance requirements. Some plants require constant pruning and division to retain their vigour and keep them clean, while others are hardy and undemanding.
They can be a fantastic long-term investment given that they can bloom and grow season after season. Even perennials with a short life span can be propagated via reseeding to keep their population going. Once established, most perennials demand less water, which is especially beneficial for growers who live in drought-prone areas and wish to conserve water. Perennials have the added benefit of providing a welcoming habitat for pollinators and local wildlife.

Are dahlias perennials or not?

Native to Mexico, dahlias prefer warm weather and cannot stand frost. They are not typically considered biennial flowers. By definition, a biennial plant is a flowering one that has a biological life cycle of two years. That is, it grows its roots, leaves, and stems in the first year, often staying low to the ground, and then remains dormant in the winter. Before dying in the second year, it grows taller blooms with flower heads that are the size of a dinner plate. They are valued for their vivid late-summer and autumn blossoms.

Many pink dahliasDahlias, on the other hand, are a type of perennial flower. They re-sprout from their underground tubers to blossom each year in their natural warm environment. This will not typically happen in the UK since the tubers will be affected by the cold winter soil. Therefore, the term tender perennials,” better fits in. 

The average perennials continue to grow and bloom year after year. The above-ground plant dies back to the ground each year in many situations, but the roots, tuber, bulb, or rhizome stay safely tucked away beneath the soil. In the case of dahlias, this is true, but only to a certain extent. The tuber will die if the soil is too cold during the winter months. If this happens, you’ll have to plant new tubers next year

As a result, many home gardeners treat dahlias as annuals, buying and planting fresh ones each year. Others pull up the tubers and store them for the winter, then replant them the next spring. It’s critical to keep the soil uniformly moist, but not soggy, or the tubers may rot.

How to care for them

Dahlias grow relatively easily, especially for such beautiful blossoms. They, like many tuberous cultivars, are grown from tubers that can be started indoors in early spring and transported outside after the first frost is no longer a threat. You can also wait till the soil has warmed and dried a bit in the spring before planting them outside.

A woman hand holding an orange dahlia

Large tubers should be planted 15 to 20 centimetres deep, while smaller tubers should be planted 7 to 10 centimetres deep. Choose a location with plenty of light and water them often to ensure they grow well.

You’ll be treated with the best reward! A big bonus on your vegetable garden full of lovely, bright, and showy blooms within a few months. Once the core dahlia flowers have fully opened, they are ready to be cut. To ensure that they are long-lasting, cut flowers in the morning when the plants are well hydrated. Those with large flowers will require staking. To seal the stems once you’ve brought them inside, submerge them in 5 or 7 centimetres of hot water but not boiling. Wait until the water has cooled before arranging them as desired. Here are some more tips that you should keep in mind.

Light

Dahlias require full sun and adequate air circulation to flower successfully, preferably at least six to eight hours a day. They will flourish better with a little shade during the peak afternoon hours when the sun is very intense. Otherwise, the heat and sun rays can burn the plants.

Soil

Dahlias prefer a nutrient-rich, well-drained soil type with plenty of organic matter and a pH of around 6.5. If you’re planting dahlia tubers in containers ahead of time, add a little garden soil to help retain moisture. Because potting soil dries out rapidly, it’s critical to keep the tubers moist until they’ve established enough roots. The tubers also need to be surrounded by a thick layer of mulch to keep them warm

Water

Dahlias, particularly young plants, do not require a lot of water to grow. Overwatering dahlias might be a big problem, as too much water can lead to decay. Because the dahlia‘s roots are close to the soil’s surface, regular summer rainfall is usually sufficient.

Woman with water can and dahlias flowers
Plan to supplement with additional watering if you don’t get an adequate amount of rain in seven days or so (or if the weather is particularly hot). It is vital, however, that they should never be allowed to dry out because they are not deep-rooted which means that a dry top layer of soil will result in a dry plant.

Temperature and humidity

Dahlias struggle to establish themselves in cold soil and freezing temperatures. Therefore, timing is crucial when planting and growing them. Wait until the last frost has passed and the ground temperature has reached around 15 degrees Celsius (you can start your tubers indoors if you want but consider mulching to retain good moisture). Furthermore, while dahlias prefer humidity when stored as tubers, they do not require additional humidity when grown outside in the spring and summer.

Fertiliser

During the growing season, the use of fertiliser on dahlias is very beneficial. The more plant food they consume, the larger their roots become and the bigger their blossoms will be. If you use fertiliser, seek one with a low nitrogen ratio and don’t fertilise your plants after August. You’ll be excavating and storing the tubers soon, and you want them to be ready to go dormant as quickly as possible.

Winter care

As the colder months approach, you may need to dig up your tubers and store them in a frost-free area. Given that dahlias are tender perennials in the UK, special care must be provided to protect the tubers from the danger of frost. Tubers are the herbaceous plants’ fleshy, overwintering root structures, which are usually dug out each autumn and stored in a frost-proof garden shed.

Dahlias in many colours on a wooden table

The easiest approach to get them to grow again is to soak them for a couple of hours in a bucket of lukewarm water before planting them into plastic pots. Finding the right size when it comes to pots is really essential. Use good quality and soil-based potting compost and then plant to the proper depth so that the top of the tuber (the leftovers of last year‘s flower stalk) is just below the compost’s surface.
If the tubers are huge and were dug and overwintered by you, they may need to be divided before being potted. Make sure each division has at least a couple of “eyes,” (the developing points much like potatoes) at the top of the tubers from which the new shoots will emerge, by cutting with a sharp knife.
Before placing the pots somewhere light and frost-free but not too warm, water and mark them carefully. Just make sure they have enough frost protection in the form of layers of horticultural fleece on chilly nights. Below are useful tips to follow when winter is around the corner: 

A hand holding a dahlia flower

  1. Cut the tips off your dahlia plants in late October to encourage tuber formation.
  2. Dahlia stems should be pruned to 7-14 centimetres from the ground level in November.
  3. Remember to name the stumps so you can keep track of which varieties you have.
  4. Dig down to about 20-25 centimetres deep around each dahlia plant using a fork. Make sure you don’t break the brittle tubers. Lift them slowly out of the hole after loosening the soil. Be patient! Dahlia tubers that break when being dug up may no longer be viable.
  5. Remove any surplus soil or compost from each tuber’s surrounding area. Organic items such as thin or decaying roots and leaves should be removed. This will aid in the prevention of fungal infections, aphids, earwigs as well as other ailments.
  6. Remove the ‘mother root,‘ or tuber from the previous year. Give about a week of upside-down storage to allow the tubers to heal. Keep in a dry, frost-free place. Dahlia tubers must be kept dry.
  7. Fill a tray or box with sawdust, dry compost, or vermiculite in an even layer. If you happen to live in a particularly colder region, cover with cardboard boxes or add some extra quilt.
  8. Keep an eye on the dahlia tubers you’ve planted. If they become too dry, use a trigger spray to mist them with water.
  9. To avoid infection, get rid of any decaying or moulding roots.

Dahlias are undoubtedly one of the greatest plants for creating long-lasting displays of brightly coloured blooms. Indeed, dahlias are perennial, but with the UK’s ever-changing weather, they are very tender and you now know how to provide them with the special care they need. 

 

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