Dahlias are beautiful, often brightly coloured flowering plants that are related to the sunflower, zinnia, chrysanthemum, and daisy. They are grown from tubers but it’s important to keep in mind that if the quality of the tuber is not excellent, it will not be possible to grow a viable flower. When planting dahlia tubers, you’ll need to do so in the early spring after the last frost. Dahlia’s love moist conditions with moderate temperatures but hates a heavy freeze. To have the most success in planting these delightful flowers, you’ll need to arm yourself with knowledge, and one of the first things that newcomers to the plant ask is how to tell if dahlia tubers are dead. In this guide, we will be looking at key signs that dahlia tubers are dead – also known as dahlia tuber rot and what you might be able to do about it.

How to Tell if Dahlia Tubers are Dead
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What Are Dahlia Tubers?

Dahlia tubers are the underground storage organs of the dahlia plant. They play a crucial role in the plant’s life cycle, ensuring its survival during dormant periods and providing the necessary energy and nutrients for growth and blooming in the active growing season.

Here’s a detailed breakdown of dahlia tubers:

  • Structure: Dahlia tubers look like a cluster of brown, elongated potatoes. They are fleshy and filled with starch, which the plant uses as an energy source.
  • Eyes: Each dahlia tuber has one or more “eyes,” which are the growth points from which new dahlia shoots emerge in the spring. These eyes are vital for propagation, as a tuber without an eye won’t produce a new plant.
  • Function: The primary function of the tuber is to store energy and nutrients. During the growing season, the dahlia plant channels energy into the tuber. When the plant goes dormant in the winter, it relies on these reserves to survive and then regrow in the spring.
  • Propagation: Dahlia tubers can be divided and replanted to produce new plants. Each section of a divided tuber must have at least one eye to grow into a new plant.
  • Overwintering: In colder climates, dahlia tubers are often dug up after the first frost and stored indoors during the winter to protect them from freezing temperatures. They are then replanted in the spring.
  • Difference from Bulbs and Rhizomes: While tubers, bulbs, and rhizomes all serve as storage organs for plants, they have different structures. Unlike the layered structure of bulbs (like onions), tubers are solid. Rhizomes, on the other hand, are horizontal stems that grow underground and can produce shoots and roots.
  • Cultural Importance: Dahlias, with their origin in Mexico, have been cultivated for their beautiful blooms and edible tubers for centuries. The tubers were even consumed by indigenous peoples as a food source before the Spanish conquest.
Dahlia Tubers
Dahlia Tubers

How To Tell If Dahlia Tubers Are Dead

Dahlia tubers can be dead for a variety of reasons including insect attack, dry soil conditions, and over-watering and if a dahlia tuber is rotten, it will not grow. It’s easy to tell if the tuber is rotten to the point of ‘death’ since you’ll be able to feel a soft spot. You may also notice visible mould growing on the end of the tuber; by squeezing it gently, you’ll be able to tell whether this is just surface mould or something that runs deeper.

How to Save Rotten Dahlia Tubers

In many cases, a rotten dahlia tuber won’t be any good and you’ll need to discard it. However, it isn’t always bad news as there are times when the rot won’t have spread too far, and the tuber can be salvaged and used to grow a beautiful plant.

Step One – Sterilise Your Tools

Dahlia rot is often caused by a fungal or bacterial infection and to treat this, you will need to first ensure that any equipment you will use is sterilised to prevent further spread. The easiest way to do this is by using household bleach at a ratio of 1:9 mixed with water. Between cutting each tuber, you’ll need to sterilise your cutters or your pruning knife again.

Step Two – Lift, Inspect & Cut the Tubers

You’ll begin by lifting the dahlia tubers and inspecting them to determine the amount of rot that is present. If it hasn’t taken over the entire tuber, you can cut away any infected areas.

Step Three – Treat

Once you have cut away the problem areas, you will need to treat these cuts with a mixture of hydrated lime and sulphur in equal parts.

Step Four – Treat the Soil

If you have removed the tubers from the ground and believe that the soil is what caused the infection, you can also treat this. Using a simple fungicide should help to prevent further problems. You might also dip the tubers into fungicide to help stave off further infections once planted.

Dahlia Tubers Lifted in Autumn
Dahlia Tubers Lifted in Autumn

How to Prevent Dahlia Tuber Rot

Dahlia tubers do not cope with being waterlogged and this can cause them to rot so you will want to ensure that they are planted in well-draining soil. If your garden is prone to waterlogging, you may want to lift your tubers and store them for winter. If you live in an area that is mild, you can keep your dahlias in the soil even over winter. However, it is wise to cut back the stalks and cover the ends with aluminium foil to prevent moisture from getting into the plant. You might go the extra mile and mulch by placing a layer of dry straw over the soil to protect the tubers beneath.


Dahlia tubers are starchy bodies that contain the nutrients that the plant needs in its first stages of growth. They come in different shapes and sizes but there may be some problems you face when planting them. One of the most common issues is dahlia rot but how can you tell if dahlia tubers are dead? Simply put, visible mould and rot will be present throughout the tuber and even to the touch, they’ll feel softer than usual. For heavily infected tubers, you can consider them dead and must discard them; however, lighter infections can usually be cleared with some simple cutting treatment.

How to Really Save Rotten Dahlia Tubers Infographic

Garden Doctor Tips

“You’ll want to make sure that any surrounding plants are not drowning in water because this will cause root rot!”

“When planting dahlia tubers, it is a good idea to do so in soil that is well drained and, in a position, where the plants will get full sun!”

“Dahlias do not need to be watered when they are initially planted; this is only something you need to do once visible shoots make their way out of the soil!”

“Nitrogen can cause problems for dahlias in large amounts so always be sure not to overfeed your plants. This can weaken the stems which makes them prone to infection!”

Frequently Asked Questions

Can dahlia tubers be left in the ground?

Yes, Dahlia’s can be left in the ground over winter, but they do not like to be waterlogged, nor will they cope with a heavy frost. If you wish to leave your Dahlias in the ground, ensure the soil is well-draining and mulch with straw.

Do you soak dahlia tubers before planting?

Dahlia tubers can be soaked for around an hour before planting. This short soaking allows the tuber to rehydrate and prepares it for going into the ground

What do you do with dahlias in the winter?

Some people like to lift their Dahlia and others like to leave them in the ground. Your preference may depend on where you have them planted. If you have soil that does not drain well, you may choose to store them overwinter but if you live in a mild area and have well-draining soil, you may choose to leave them in the ground.


Trevor Wright is not just a seasoned horticulturist; he’s the esteemed Garden Doctor. With a BSc in Horticulture and years of hands-on experience in the soil, Trevor has become a trusted mentor for all things gardening. As the founder of Garden Doctor, he’s committed to clarifying the intricacies of gardening, offering straightforward advice that’s rooted in years of practice. His writing is a garden of how-tos, savvy insights, and comprehensive guides that enable individuals to nurture and grow their garden dreams. When he’s not knee-deep in garden beds, Trevor is at his keyboard passing on his green-thumbed wisdom to budding gardeners, ensuring that the legacy of sustainable and joyful gardening blossoms far and wide.

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