How to overwinter dahlias like Monty Don so they bloom year after year

Learning how to overwinter dahlias will grant you almost magical powers: you'll be able to keep your dahlias alive over the cold winter months. But how do we best go about making your dreams of overwintering a reality?

Well, by paying attention to the advice dished out by gardening guru Monty Don, of course! Because, with his expert help, you'll see those bold bright blooms return year after year – no small thing, especially when you've spent all that time learning how to deadhead dahlias already.

Here's how to get started, then, on the seriously clever garden trend of overwintering dahlias...

How to overwinter dahlias

We know, we know: once you've overwintered one tender plant, surely you've overwintered them all?

Wrong! Unlike the process for overwintering geraniums, learning how to get overwintering dahlias doesn't involve rushing your precious flowers indoors and coddling them at the first sign of autumn. Far from it, in fact.

'Frost reduce dahlias to blackened tatters so it will be time to bring them in,' explains Monty Don via his popular gardening blog. 'However the tubers will not be harmed unless the ground freezes, so do not panic.' 

Monty's preferred method of overwintering? Lifting them, obviously.

'Wait until the top has fully died back and then cut back the top growth to 6 inches whilst they are still in the ground and carefully dig up the tubers, removing as much soil as possible,' he says. 

'Stand them upside down for a few days to drain any moisture from the hollow stems and to let the tubers dry a little and then store them in a tray or pot packed with old potting compost, vermiculite, sharpsand or sawdust.'

'The idea is to keep them cool but frost-free, dark and dry but not to let them dry out completely or else the tubers will shrivel,' adds Monty. 

'I lightly water mine after layering  them into large pots or crates and then check them every month to see if any are mouldy or shrivelling up.'

Of course, if you really want to learn how to overwinter dahlias like an absolute pro, there are other methods you can try. Look this way, then, for more...

What you will need

If you're hoping to learn how to overwinter dahlias properly, you will need...

• A good pair of secateurs
• A garden fork
• An unheated shed or garage
• Labels
• A cardboard box lined with newspaper/brown paper bag
• Dry sand, soil or compost

How to overwinter dahlias in pots

If you've been busily growing dahlias in pots this year, then you're in luck: it's incredibly easy to overwinter these little beauties.

'Bring the pot into a dark, unheated garage or frost-free shed,' says Morris Hankinson, director of Hopes Grove Nurseries. 

'Let the compost dry out completely over the winter, and remember that it’s a good idea to cut back the top growth by about half (not down to ground level).'

Morris Hankinson

Morris Hankinson is the founder and managing director of Hopes Grove Nurseries Ltd, the UK’s only specialist grower-retailer of hedging plants, which he established after graduating with a Commercial Horticulture Degree from Writtle College, Essex in 1992.

In the spring as temperatures rise, you should start to see some new growth from the base. This is the time to bring the plants back into the light and start watering them, but still working hard to protect them from late frosts. 

'You might like to repot them into a larger size, or at least tease out some of the old compost and freshen the pot up with some fresh new compost around the roots,' says Morris. 

'This is also the time to trim those old stems back to make them tidy and you should be set for another summer’s enjoyment of these lovely plants.'

How to overwinter dahlias in garden borders

If you've been growing your dahlias in garden borders (or anywhere in your garden, to be honest), don't despair: there is, of course, still a way to overwinter them - you need to get overwintering dahlia bulbs, more specifically.

'These colourful plants overwinter from one year to the next by means of their fleshy tubers underneath the soil,' says Morris.

'The key to successfully keeping these plants from one year to the next is to preserve the tuber by protecting it from rotting or becoming frozen.'

Wait until the foliage on your dahlias has been blackened by the first frost. Then, cut off the old flowering stems about 5cm from the base (chuck them in your hot compost bin when you're done), and use a fork to prise the plants out of the soil.

Use your hands to brush the soil away from the tubers, taking care not to bruise or damage them at all, then hang the healthiest-looking ones upside-down in a cool place to dry off.

The final step in overwintering dahlia bulbs is to transfer your tubers to that aforementioned cardboard box, cover them in dry sand, soil or compost, and leave them alone in your garage or shed. (Hint: it's a good idea to label them, so Future You knows what their dealing with).

When spring rolls around, all you have to do is dig out the tubers, give them a short soak in warm water to wake them up, and plant them in warm spring soil (ideally, you want it to be around 15°C).

Alternatively you can start them indoors in pots and then plant out when they are in growth.

FAQs:

Sounds almost too easy, right? We're off to learn how to overwinter dahlias right now, then, if you'd care to join us...