How to Grow Dahlias Successfully

Dahlias are one of the garden flowers that are most underestimated in my opinion. Not only are they an incredible source of food for the bees, their roots are also edible for humans. They come in all sorts of colours and flower for up to 5 months of the year or more if you are lucky with the weather. In our garden we have about 20 different varieties, most of them are from seed and of the open daisy variety. These are better for wildlife as they have pollen that is accessible for bees. We have a couple of pompom varieties as they are stunning, however these are more prone to root rot and disease. Here is my guide on how to grow dahlias successfully to ensure that you have a long season with flowers.

There are a few things to consider but none of them are hard to do or complicated. In fact dahlias are incredibly easy to care for and provide a very long flowering season and there is a type and colour for everyone. Let me just tell you that the National Dahlia Collection of the U.K. consists of over 1600 named species – just to give you an impression of the vast amount of choice that you have. You are simply bound to find one that you like.

Your biggest enemy: slugs.

Firstly I need to make it clear that dahlias are sadly a favourite snack of slugs and snails. If you intend to plant them you need to make sure that you can keep the snails away from the plant. Once they reach a certain height they are okay as the snails only like to eat their leaves and shouldn’t be able to reach them, so stay vigilant in the spring when the shoots are fresh and short.

Soil and planting.

To get a proper, long flowering season out of your dahlias it is important to think about the ground where you plant the tubers. Dahlias like semi shade to full sun, as long as they have some sun it will happily flower for you. The soil needs to contain a generous amount of nutrition but most importantly it has to allow for proper drainage. Plant your dahlia tubers about 10 cm’s (4 inch) deep in the ground or in containers and make sure they have plenty of drainage – very few plants like being soggy. When it comes to fertilising you can consult your local garden center or stick with natural sources. I usually get horse manure for mine as this is odor free and safe for vegetables. Once you’ve got a dahlia established it will not need much other than the occasional watering in the summer. 

Keeping them safe during winter.

We leave our dahlias in the ground here in Southern England, but if you live in an area that has hard frosts or a lot of rain it is important that you take them out after the first frost killed their leaves. Store them in sand or damp compost in your shed/garage/shack over winter and plant it back out as the weather heats up. A great tip that I was taught long ago was to turn your tubers upside down in the start of the winter – that way the tubers will dry from the bottom ensuring that they do not start rotting. If you do decide to leave them in the ground it is important that you mulch them with bark or any other good mulch. Mulching means you cover the ground above the tubers with a thick layer of bark or mulch. You can get that at any garden center. This will make sure that the tips don’t get damaged by any light frosts. Do not cover your plants with plastic sheets, this will effectively rot your plants as the moisture has nowhere to go. 

Maintaining a flowering dahlia.

Once they get to flower around June (May in warmer areas) it is important that you start deadheading spent flowers. Deadheading sounds barbaric but it is necessary to provide you with healthy and beautiful dahlias for as long as possible. It means nothing else but taking the spent flower heads off the plant, hence deadheading. You can differentiate buds from spent flowers by looking for buds that are long rather than circular. If you keep doing this they will keep flowering until the first frost, however if you let them set seed they will stop producing new buds. The spent flowerheads are easy to spot. They look like buds at first sight but they are squishy and come with very yellow tips. Buds are round and very firm, almost rock hard. On the picture below you can see spent flowerheads of three different varieties and they are all strikingly similar.

Do not worry about wasting flowers, the quicker you remove them the quicker you will actually have new flowers and they will flower until the first frost. If you are concerned you might pick the wrong heads then you can look for flowerheads that started losing petals and pick them off as soon as that happens. I tend to already pick them off when they look like in the picture below.

Dahlias are edible.

Dahlia tubers are also a great addition to any dinner – they are closely related to jerusalem artichoke and sunflower. They taste a bit like water chestnuts mixed with carrot and do really well in salads. But it isn’t just the tubers. In mexico the petals are also used to be delightfully coloured teas. The dahlia originates from South and middle America, in fact the indigenous people of South Mexico named the Tree Dahlia “Water Cane” as it has such a high amount of water in its stems. Dahlias store water in their stems to prop them up, which is why they also suffer so much in the first frosts of the year.  

Trivia: growing and hybridizing dahlias used to be a real competition.

A fun fact to mention is that dahlias used to be somewhat of a craze around the 1850’s in Europe. Everyone from the poor to the upper classes were competing with each other on who had the nicest looking hybrid. Due to this it has very much been forgotten as a food crop, but if you want to try it out then harvest some of the fatter energy storing tubers when you lift your dahlias in the autumn.

It is important to mention that you are more likely to have great tasting tubers from heirloom varieties. This is due to the fact that the plant is genetically much closer to the original species that was brought over from the new world. This means that the open varieties are probably your best bet for consumption. Open varieties are the ones that look like daisies like the picture above. By sticking with the open varieties you also offer bees and bumblebees a lot of food since they come with a lot of pollen. Look at this little bee that has literally planted his tiny face into it.

Quick recap.

To summarise on how to grow dahlias successfully:

• Prepare your planting site with horse manure and grit if you have waterlogged soil.
• Ensure that there is some sun.
• Deadhead spent flowers.
• Protect the tubers from hard frost and waterlogged winters. Most dahlias do not die from frost but from rotting due to too much rain.

Once you’ve got the basics down the plants will keep giving you wonderful food and flowers for years to come. I hope you enjoyed my guide on how to grow dahlias – please feel free to share any pictures or tips that you have when it comes to growing them in your garden.

Enjoy the additional pictures below from my garden – I will soon write a guide on how I grew these from seed which will help you save a whole lot of money. Tubers are expensive!

This dahlia was my first seedling that I grew from some seed I got from an old neighbour – it’s a bit spiky and not the prettiest but it taught me a lot about how to grow dahlias. The bees absolutely love this one – so I am keeping it.

This pompon variety was my first successful cutting – it is now in it’s 3rd year and is looking fabulous. An important aspect to consider when growing dahlias is that varieties like the one in the above picture do not feed any wildlife as the pollen and nectar is enclosed behind all those petals. I’m a big advocate for picking open varieties when it comes to how to grow dahlias.

This is one of my open varieties and the picture doesn’t do it justice. It has the most vibrant shade of pink.

                Another spiky looking one but unlike the other one this has light coloured foliage.  

This cardinal red variety is of a really rich and velvety colour. It was part of a mixed seed package that I bought back in 2013. It has strong stems and holds its flowers for longer than any other dahlias that I have.

By far one of my favourites is this peach and light pink coloured one. It has a hint of yellow in the center and looks almost too perfect to be true. I simply adore it.

This is a bicoloured variety that usually grabs the most attention when people visit. I have often been asked if it is actually real.

Another pink variety that is almost red in the center. It has beautifully gradient leaves and it rather small for a dahlia. It is not being bigger than the palm of my hand but strikingly beautiful.