There are hundreds of different varieties of dahlias. All dahlia plants produce stems of single flowers ranging from 2 inches in diameter to a foot wide. Most dahlias do not produce any scent and attract pollinators through their bright colours. Dahlia plants also range in height with some as little as a foot tall and others growing to upwards of 6 or 8 feet in height.

 

Where to grow dahlias

Dahlias like a sheltered spot with as much sun as possible, a south or west facing border is ideal. They are not too fussy when it comes to what type of soil they are planted in as long as it drains freely. Tubers left in boggy wet soil will not grow very well and will fail to bloom.

 

When to plant tubers

Don’t be tempted to plant dahlias outside too soon. Most dahlia varieties aren’t very frost hardy and they can quickly perish in very cold weather since they are a tuber and not a bulb. Get them started in a greenhouse from February or outdoors after the last frosts when the soil has warmed up. Depending on where in the UK this is it could be March or late-April.

 

How to plant them

Soaking tubers in tepid water for an hour or so gets them off to a great head start. It is not entirely necessary as the wet soil will eventually wake them up but a good soak nevertheless rehydrates them faster.

Starting the tubers off in pots first will encourage them to develop faster, giving blooms sooner. If they are being left in pots ensure there is sufficient space below the tubers for the roots to grow. A 20cm pot will be enough space for one dahlia plant.

When planting directly into the growing site start by digging a 10-15cm deep hole and place the tuber into it. Cover it over leaving the tip of the shoot just under the soil. Dahlias need 30cm of space between them to allow air to flow freely. If planted too close there is risk of pest problems on the plants as they become larger and more crowded.

Once planted, water in well to settle the soil around the tubers. Dahlias have all the nutrients stored in their tubers that they need to get started; they can now be left to their own devices.

 

Ongoing care

The tubers will take about four weeks to really show above the ground though this is dependent on temperature. Don’t worry if they are slow to get going, they won’t grow until they are ready.

Watering: Young plants won’t need watering until they have their first set of true leaves, then they will need at least a good soak twice a week.

Staking: Tall varieties can become top heavy and need to be staked. There is nothing more disheartening than when a strong gust of wind decimates a well-cared for plant. Bamboo canes or tomato plant cages are ideal.

Pinching: When the plant reaches about 45cm high or has four pairs of true leaves they benefit from a little trim. This will delay blooms for a couple of weeks but in the long run the plant will produce many more flowers. Remove about 10cm of the centre stem leaving just three pairs of true leaves. This will encourage the plant to branch out and grow more flowers from the sides.

Taking Cuttings: Cuttings can easily be taken from new plants; you can have as many as seven new plants from one tuber. See our blog post on how to take dahlia cuttings,

Deadheading: As flowers fade pinch them out and more will grow, keep doing this and a dahlia will continue to bloom right up until the first frost.

 

Lifting and storage

Dahlias will not survive heavy frosts over winter so they are best lifted for storage until next spring. If they have been planted in pots, the pots can simply be stored somewhere cool and dry. If they are being lifting the from the ground then it is recommended to either wrap them in paper, store them in dry sand or soil for the winter.

 

Propagating

Once they are large enough dahlia tubers can be split to form an identical plant. Collecting seeds from the flowers can give varying results depending on nearby varieties that insects will have pollinated them from. If propagating by division it needs to be done when the plant has gone dormant.

Each year the mother tuber (the original bulb) typically produces anywhere from 5-20 new tubers. By dividing these tubers in the winter, the plant can be multiplied for growing identical dahlia flowers.

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