The relatively warm weather through November and the start of December has meant that the Dahlias have kept going longer than might otherwise have been expected; the first frost was only experienced at the end of the first week of December, the Dahlias blackening under the touch of icy fingers.
Dahlia tubers will continue to grow until the first frost, after which the choice is either to lift or to mulch. This year we will lift and store the Dahlias; though planted in a raised bed, this part of the garden can suffer severe flooding during the winter months so the risk in leaving them in the ground is not worth taking as they will likely rot.
Use a fork to gently loosen the soil around the tuber and lift the clump, tapping off the soil. Place the tubers upside down in a crate to allow the water to drain fully from the hollow stems, and leave in this position for about week. Ensure that they are not left somewhere where rodents can get to them and that they are not left anywhere frosty.
After a week place them a box or crate and cover in old compost, coir or vermiculite, keeping the crowns uncovered. They must be dry but not left to dry out completely, so check the once every few weeks and give them a light watering if ncecessary. Store them in the dark, again in a frost and rodent free place.
Having dried them, and before packing them away for the wtiner, you can divide the tubers or they can be left in a clumo to divide in the spring.
When done properly, digging and dividing will keep your dahlias returning year after year. Dahlias left in the ground will create a massive tuber clump underground that will send up many weak, unproductive stalks that have small blooms. Eventually these won’t come back at all.
Tap and brush all the soil off the dahlia clump. When dividing dahlias, the first thing to do is to remove all broken tubers, remove the original ‘mother’ tuber and remove any tubers that are rotten. You can divide now or keep the cleaned-up clump in tact and divide in the spring. In the spring, the eyes are easier to see. It’s very important to get a piece of the swollen part that is attached to last years’ stem and from which the eyes will emerge. If your tuber does not have an eye, it will not sprout. Choose only strong, firm tubers. Weak tubers that show signs of rot, shriveling or decay should be tossed and not used in the garden.
Cut surfaces should be allowed to dry thoroughly before they are planted in the garden or stored for the winter. Lay out to dry for 3-5 days in a place that will not freeze, then store for the winter.
In the Spring
Another advantage of lifting Dahlias is that they can be potted up in early spring and with a little heat and protection forced into producing new shoots that can be taken for cuttings. These should root very quickly if cut off from the junction of the tuber when they are about 7cm (3in) long; do this every year and you’ll have a vast store of Dahlias to brighten your garden late into the year.
If using this approach, the cuttings should be ready to plant out in about July, whilst the parent plant should can go outside in mid-May, or once the risk of frost has passed. If you choose not to take cuttings in this way then the overwintered tuber can be planted out in early April in good rich soil and at a depth of about 15cm (6in).
The result will hopefully be this: