Although Dahlias are perennial, they are also tender. Special care is needed when storing their tubers to protect them from hard frosts.
As the colder months encroach, you will need to dig up your Dahlias tubers and store them in a frost-free environment.
How to overwinter Dahlia tubers
- During late October, cut the tops of your dahlia plants to encourage tuber development.
- In November, cut the stems of your Dahlias to between 3-6 inches from the ground level. Don’t forget to label the stumps so that you can keep track of each variety.
- Dig down to about 8-10 inches deep around each Dahlia plant with a fork. Ensure that you don’t damage the brittle tubers. Once you have loosened the soil, lift them slowly out of the ground. Be gentle! If Dahlia tubers snap during the digging process, they may no longer be viable.
- Remove any excess soil or compost from around each tuber.
- Remove organic materials such as thin or decaying roots and leaves. This will help prevent fungal infections and other diseases.
- Remove the ‘mother root’ or last year’s tuber.
- Leave to upside-down for a week to allow the tubers to heal.
- The Dahlia tubers must remain dry but not dry out completely.
- Place in a dry, frost-free environment.
- Evenly space in a tray or box and fill with sawdust, spent dry compost or vermiculite.
- Cover with cardboard or add an extra quilt if you live in a colder climate.
- Keep an eye on your Dahlia tubers. If they dry out, spray a little water on them with a trigger spray.
- Discard any rotten or moulding roots to limit infection.
An alternative to lifting tubers
If you live in a milder part of the UK, then you might want to leave your Dahlias in the ground overwinter. I like this method as it offers very little disruption to the plants. You will need to cover each rootstock with a ‘molehill’ of spent compost. This will act as a blanket against hard frosts. Feed your Dahlias with fish bone and blood during late spring.
Dahlias – when to plant – UK
Your tubers have survived the winter and now it is time to plant them out again. The following is a description of when to plant your Dahlias if you live in the UK. Times and techniques may vary for other countries.
- Carefully place tubers in 2-3 litre pots of free draining, general purpose compost during March to early April.
- Cover each Dahlia with compost so that only the stump is visible. Don’t bury deeply. Dahlia tubers grow immediate beneath the soil level.
- Place pots in a frost free and bright location.
- Water your Dahlias. Don’t over-water, but ensure that the compost doesn’t dry out. Boggy compost will rot your tubers.
- After the risk of frost has passed, plant them in a sunny spot, in a fertile and well-drained soil.
- Space each Dahlia between 50 cm – 75 cm.
- Mulch around your plants with a 3 cm layer of compost. This will help retain moisture and block some weeds from competing with your Dahlias.
- Flowering should start in early July.
- Dead-head your Dahlias daily.
- Enjoy until early December and then overwinter your Dahlias for next year!
If you have enjoyed this guide on how to overwinter Dahlia tubers, perhaps you would like to read our Overwintering Begonias post.
Geoff Hoyle, Dahlia expert
Here is a great video on everything you need to know about getting the best out of your dahlia plants. It is by Geoff Hoyle, a keen Dahlia grower in Bredbury, Cheshire. He not only takes you through planning, planting, staking and propagation, he also explains how to over winter Dahlias in great detail.