What to do with dahlias in October – 3 crucial tasks to keep them thriving this autumn

Autumn is still peak season for dahlias, with plenty of plants still in bloom – but knowing what to do with dahlias will ensure you look after them properly during and after flowering.

Whether you’re growing dahlias in pots or borders, you’ll want to make the most of the blooms this month, while the rest of the garden winds down for the year. To do that, you’ll need to stay on top of a few simple maintenance tasks – and those depend very much on which part of the month it is.

Here’s what you should be doing with your dahlias this October, before and after they finish flowering.

What you'll need

1. Deadhead spent flowers

If your dahlias are still blooming (and many are at the start of October), you’ll probably want to extend those displays for as long as you can.

Enter deadheading: the unsung hero of flowering plants. The more you remove spent flowers, the more energy your plant will have to spare for extra blooms – and that's why deadheading is such an important task for abundant dahlia displays.

'In October, I would keep an eye on the weather and let the flowers continue for as long as possible,' adds Ross Dyke, Hornby George's consultant horticulturist and host of The Plant Pod.

2. Leave the foliage alone

Even if your dahlias have finished flowering, it’s still too early to cut them back for the winter. The ideal time to cut dahlias back is actually much later on, when the weather has cooled down.

‘Leave dahlias untouched while the foliage remains healthy, cutting them back after the first frost has blackened the leaves,’ says Annelise Brilli, Thompson & Morgan's horticultural expert. ‘This allows the plant to replenish the tuber’s energy.’

3. Cut them back after the first frosts

This October's weather forecast looks very mild, but in colder regions of the UK, the end of the month might bring the first frosts – and that gives us the green light to cut the foliage back.

'Once the first proper frosts arrive and the foliage starts to turn black or die back, I'd cut the stems down and decide whether to leave the tubers in the ground or lift them for winter,' says Ross.

Use a clean, sharp pair of bypass secateurs like the Spear & Jackson Razorsharp Advantage Bypass Secateurs from Amazon. If you'll be overwintering your dahlias and lifting the tubers, make sure you store them somewhere cool and dry.

'If I'm leaving them outside, I'd give them a good layer of mulch to help protect them from cold and wet conditions,' Ross adds.

RocketGro Peat-Free Organic Magic Mulch, which you can buy from Amazon, feeds the soil and suppresses weeds, too.

These October dahlia tasks are simple but key – and they'll ensure the tubers conserve as much energy as possible for the next growing season.