How to grow dahlias successfully in your garden

Our gardening expert Tom Brown reveals the best way to get the most from these summer blooms in 2022

Soil fertility is key when it comes to growing dahlias and these blooms tend to be ravenous

Over the years I have learnt that dahlias, like delphiniums, need a few key factors to thrive. 

We shouldn’t be planting out dahlias until the end of May, when the risk of frost has passed, but if you’re planning on growing them this year, here’s my advice.

Happy gardening! 

Top tips for growing dahlias

The first rule of dahlias to be aware of is that they don’t like competition around them. I have tried growing dahlias in a mixed border but found that they detest being overshadowed, and having to fight for water and nourishment. Dahlias need space, especially when young. I have had the best results from growing dahlias in their own bed or in a veg patch where I can provide all the water and fertiliser they need.

If you must grow them in a border, allow approx 40cm all around young plants to give them the space they need to get established.

The second key condition for growing dahlias is protection from pests. Young dahlias act like a green magnet for slugs and snails, which hide in borders and then come out to feast at night. There are many different ways to manage slug populations but I’ve taken inspiration from a nursery that battles with slugs on their delicious hostas. At Sienna Hostas they use a homemade garlic wash on plants each week.

But be warned: after making this brew your kitchen will smell to high heaven for a short while so a camping stove in the garden might be in order.

Finally, soil fertility is key. Dahlias are as hungry as they are thirsty. Before planting, fork two bucketfuls of well-rotted manure or compost into the planting space. Once planted, sprinkle a handful of fish, blood and bone around the base of plants.

Repeat this application every month and from June add a handful of sulphate of potash to help with flowering performance. Aim to water dahlias with one watering can per plant, per week, and increase this during the height of summer and during dry periods.

As for suppliers, Withypitts Dahlias supply Covent Garden with first-class cut blooms and also supply a wide range of plants via mail order..

This article is kept updated with the latest advice.