Should you leave dahlias in the ground over winter or not?
The dahlia is the star of late summer: it continues to bloom well into autumn. But as soon as the first frost approaches, the same question inevitably arises every year: can you leave dahlias in the ground over winter, or should you dig them up? The short answer: yes, you can—but it's not without risk.
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Dahlias are native to Mexico and Colombia and are not cold-hardy. Their tubers are succulent and contain a lot of water. As soon as the temperature drops below freezing, that moisture freezes and damages the cells. The result: soft, rotting tubers that no longer sprout in spring.
The general wisdom is: dig up the dahlias after the foliage dies back, clean them, and store them dry and frost-free – for example, in a shed or cellar. This way, they'll stay safe until you plant them out again in spring.
It's quite a lot of work to overwinter your dahlias by digging them up every year. And not everyone has a suitable place (cool and dry) to store the tubers. That's why many gardeners wonder: can I leave my dahlias in the ground?
That's possible – but only if the conditions are right:
- Your garden is located in a region with relatively mild winters , for example on the coast.
- The soil is well-drained – sandy or light loam, not heavy clay.
- The spot is sheltered , for example against a wall or along a hedge.
The most important thing is that the ground doesn't freeze too deeply. As soon as the temperature drops below -5°C, the tubers risk freezing beyond repair.
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Even if conditions aren't ideal, you might still be able to leave dahlias in the ground. You'll need to take additional precautions, though:
- To start, cut the stems back to about 10–15 cm above the ground.
- Then place a thick layer of mulch of leaves, straw or compost over the plant like a blanket.
- If necessary, cover the ground with an inverted pot or crate to keep out the worst of the rain and cold.
- Tip: Label the plants clearly so that you know where each species is in the spring.
Dahlias can easily survive a mild winter and sprout again in the spring.
Do you have heavy clay soil or live in an area of the country where frost is often harsher than elsewhere? Then it's safer to dig up your dahlias. Clay soil retains water, and it's precisely that combination of cold and dampness that is detrimental to the tubers. And in colder areas—or during a harsher winter—a layer of leaves or compost won't adequately ward off frost.
If you don't want to risk the tubers freezing, you should dig your dahlias out of the ground. Here's how:
- Wait until the foliage has died back after the first frost. The stems will then turn black.
- Use a rake to dig the plant out of the ground. Avoid poking the tubers.
- Wipe off any excess soil (don't wash them with water!) and let the tubers dry for a few days.
- Store your dahlias in a cool, dark, and frost-free place – for example, in a wooden box with some newspaper or sawdust.
- Check occasionally that the tubers are not moldy or shrivelled.
Tip!
So, it depends on whether it's better to dig up your dahlias or leave them in the ground. Still unsure? This decision-making guide will help you quickly see what works best in your garden.
- Yes: You can leave them on, but cover them well.
- No: Dig up the tubers and store them indoors.
- Yes: If it doesn't get too cold, you have a chance of success.
- No, clay soil: Digging it up is always better, because the soil gets too wet in winter.
- Yes: That helps protect the tubers.
- No: There is a greater risk of frost damage.
- Yes: Leave a few dahlias (well covered) in place as a test.
- No or unsure: Better to get them out of the ground.
- Yes: Digging it up and storing it properly is the safest option.
- No, experimenting is allowed: leave them in place and cover well.
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