Divide dahlias

Why divide dahlias?

Dividing dahlias is an essential practice to ensure their health, flowering, and longevity. Here are the main reasons:

• Encourage abundant flowering: Over time, clumps of tubercles become denser, which can limit flower production. By dividing your dahlias, you provide more space and energy for each tubercle to produce larger and more numerous flowers.
• Prevent plant exhaustion: When tubercles are too many or too crowded, they compete for nutrients and water. Division helps rejuvenate the plants and ensures better growth.
• Multiply your dahlias: Dividing tubercles is a natural and economical method to obtain new plants. This allows you to expand your dahlia beds or share them with loved ones.
• Reduce the risk of diseases: Overly compact clumps are more vulnerable to fungal diseases and rot, especially in humid conditions. Regularly dividing the tubercles reduces this risk by removing damaged or diseased parts.
• Adapt plants to available space: If your bed becomes too cluttered, division allows you to reduce the size of the clumps while maintaining a well-organised garden.

When to divide dahlias?

Dahlias can be divided either in autumn, when they are stored for winter, or in spring, just before replanting them in the ground. Each period has its advantages and disadvantages, depending on your experience and gardening preferences.

For experienced gardeners, autumn is often the preferred time to divide dahlias. At this time, the stems are still tender and easy to handle. Once the tubercles are dug up, it is important to locate the developing “eyes” – small bumps at the base of the stems that will become the growth points in spring. This technique requires a bit of practice and keen observation, as the eyes may be less visible than in spring. After division, the tubercles should be stored in ideal conditions: a cool, dry place protected from frost, to ensure their proper preservation during winter.

If you are a beginner or have doubts about dividing in autumn, wait until spring. At that time, the eyes are well-formed and often already starting to sprout, making them easier to identify. You will then be able to cut the tubercles more accurately and avoid mistakes. The downside of spring is that the stems may have hardened and become more difficult to cut. However, with a sharp knife or quality pruning shear, this step remains entirely feasible. Once divided, the tubercles can be replanted immediately for quick and vigorous regrowth.

How to divide dahlias?

To divide dahlias, equip yourself with a sharp knife or clean, disinfected pruning shears to limit the risk of disease transmission. Then follow these steps:

• If you are dividing your dahlias in spring, take them out of their winter storage. If you are doing this in autumn, dig them up. In both cases, clean them to remove excess soil and facilitate handling.
• Using clean, sharp pruning shears, cut back the faded stems to about 10 cm from the base. This step allows better access to the stump and makes it easier to work.
• With a sharp, disinfected knife, make an incision in the centre of the stump, between two stems, taking care not to damage the tubercles. Ensure that each section has at least one bud (or eye), as this is where the new shoot will develop.
• Gently detach the pieces by hand or with the knife while preserving the tuberous roots. Handle with care to avoid breaking the tubercles or damaging the eyes.
• Continue to divide the tubercles according to the number of plants you wish to obtain. Each division must include a clearly visible eye and several healthy tubercles to ensure good recovery.
• If you divide the dahlias in spring, replant the obtained pieces immediately, either directly in the ground after the last frosts or in pots or trays filled with a mixture of potting soil and sand. This allows growth to start in a sheltered environment before planting out.
• If you divide them in autumn, store the divided tubercles for winter as usual, in a dry, cool place protected from frost.
• Don’t forget to label each tubercle with the name of the variety. This will help you easily recognise them during planting and maintain organisation in your garden.

Also discover our video tutorial on how to divide dahlias

How to care for dahlias after division?

After division, it is essential to take good care of your dahlias to ensure a strong start. Plant the tubercles in well-drained soil, enriched with compost or organic fertiliser, at a depth of about 10 cm with the buds facing upwards. A light initial watering will help to moisten the soil without waterlogging it. Subsequently, adjust watering according to the climatic conditions: keep the soil moist but avoid excess water that could lead to tubercle rot.

For large-flowered or tall-stemmed varieties, it is wise to install supports at planting. This will help to support the plants as they grow, especially against winds or the weight of the flowers. Once the dahlias start to grow, apply a potassium-rich fertiliser every three to four weeks to encourage abundant flowering. However, avoid fertilisers that are too high in nitrogen, as they would stimulate leaf growth at the expense of flowers.

Regularly weed around your dahlias to reduce competition for water and nutrients. We also recommend applying organic mulch at their base (straw, fallen leaves, wood chips…) to retain moisture and limit the proliferation of weeds. Keep an eye on your dahlias for pests such as aphids, slugs, or snails, as well as any signs of fungal diseases, and act quickly if problems arise.

Finally, remember to regularly cut back faded flowers to encourage the plant to produce new blooms.