How and when to dig & divide dahlia tubers

Early spring is a good time to dig and divide your dahlias

Though many would have chosen to dig their dahlias in autumn, which can prevent the chance of rotten tubers in wet soils over the wintertime, you can still lift your dahlias in early spring before they start to shoot. This will give you an opportunity to divide and multiply the plants in your garden. 

Spring, particularly in September, is the ideal time to dig up and divide your dahlia tubers in preparation for the next growing season. After winter, the tuberous roots of the dahlia plant are ready to be separated into smaller clumps, which can yield multiple new plants for the following year. By dividing your dahlia clumps correctly, you can expand your garden blooms with strong, healthy plants next season, each capable of producing dreamy blooms.

When dividing, it’s essential to inspect the tubers carefully to ensure that each smaller piece has a viable eye — a small raised bump at the neck of the tuber. This is where the growing point will emerge during the next season. The best way to ensure clean cuts and healthy divisions is to use a sharp knife (or chisel) and make precise incisions, avoiding damage to the important parts of the tuber, such as the neck and growing points. For best results, look for tubers with a strong neck and minimal signs of virus or disease. Removing any damaged or diseased sections will help prevent the spread of dahlia crown gall and other common ailments.

After dividing the clumps, proper storage is key to maintaining the quality of the tubers before you plant them out. Place the divided tubers in a well-ventilated container like a cardboard box, paper bag or plastic crate. You can also surround them with a storage medium such as peat moss or wood shavings to keep them dry and free from rot if you would like to. Be sure to label the different varieties so you can easily identify them when it’s time to plant. Storing the tubers in a cool, dry location will keep them safe until the risk of frost has passed and the soil is ready for planting after the last frost date.

How to Dig and Divide Dahlias:

1. Dig all around the tuber clump with a spade or garden fork. Leave a 10cm wide margin to ensure you do not damage any of the tuberous roots.

2. Lift the tuber clump with care and gently shake off excess soil if possible.

3. Use a brush (or the hose) to wash off the remaining soil from the tuber clump. This will help when dividing your clump of tubers.

4. Leave the clump of tubers to dry in the sun for one to two days.

6. You may decide to split the clump in half, quarters, or even individual tubers. But first, cut the stem down to the crown.

7. If there are any easy to remove tubers around the edge of the clump, go ahead and cut these off first, and work your way inwards.

8. Often, you may need to divide your dahlia tuber clump in half first to gain better access to it. To do this, take a chisel and hammer and split the clump at the top of the crown.

9. Continue to cut away the individual tubers with visible tuber eyes. The eyes are growth buds that are located on the crown of the tuber, this is where a new shoot will sprout. Tubers that do not have an eye are not viable tubers.

10. Remove any tubers that have broken necks, look black, soft, or have signs of rot.

11. Allow the divided tubers to heal over for a couple of days. This is when the open wound forms a seal and stops water from entering the tuber. This can prevent rot.

12. If you are located in tropical climates, such as the upper North Island, you can replant the healthy tubers directly into the garden from late September (spring). Otherwise wait until Labour Weekend (October) for other areas of New Zealand (ie. mid North Island and South Island regions). Dahlias should be planted in well-drained soil and full sun.

You may choose to pre sprout your tubers in some potting mix in pots. Keep them in a warm position indoors and you will get a kickstart on their growth come planting time in late October.