Originating from Mexico and Central America, Dahlias are favourites with gardeners for their showy displays in flower beds and pots. They also require very little maintenance and are relatively pest free. They are ideal for show entries as they reach their prime in late summer and autumn. Dahlias in particular can produce specimen blooms ideal for flower arrangements or displaying on their own in a vase.
Dahlias are warm weather plants and their foliage will not tolerate frosts. The first frosts will turn the foliage black and they may look dead but they are still very much alive at this point. However, some preparation is required if you are going to keep them for another year. Following these simple steps will ensure you can enjoy these blooms year after year.
If you have the space, then you can overwinter Dahlias in their containers. Simply remove any existing foliage* and place them in an environment where they are sheltered from the worst of British weather. A greenhouse is ideal, but if you don’t have one, then they can be stored in conservatories, garages or sheds. *Before removing the foliage it’s a good idea to label each plant, even if you just make a note of their colour.
Dahlias can survive in an unheated greenhouse, but if the temperatures go more than 3 or 4 degrees below zero try wrapping the pots or containers in bubble wrap or similar to prevent the soil freezing. Or invest in a low wattage electric heater which will keep your greenhouse frost free.
Before going into storage you need to dry out the soil as much as much as possible, but not completely. Keep the soil slightly moist. They are best kept in a humid atmosphere, but too wet and the tubers will rot.
Check the pots periodically over winter. When the risk of frost has gone remove them from storage and water lightly to encourage the tubers back into life
Keeping Dahlias used as Bedding Plants
We are lucky in the South as we rarely get severe winters. It’s tempting therefore to leave the Dahlias in situ and let them take their chances. In a mild winter there is every chance some of them will survive. However, if the soil freezes then it will kill the tubers and a very wet winter may cause the tubers to rot. Don’t forget that they will also be susceptible to soil pests.
It’s much safer to remove them from the beds and store the tubers. There is also the added advantage that the tubers can be divided to make several new plants. However, if you want to enter a dahlia in the show, keep a few undivided specimens.
Dig up the entire plants with foliage still attached before the hard frosts set in. Ensure that the tubers are not damaged in the process. Damage will often lead to rot and the death of your Dahlia. If any tubers are damaged use a sharp knife to cut away the damaged part. Look out for any Vine Weevil larvae. If present shake them out. They have huge appetite for tubers.
First you need lay out the tubers on a tray, carefully spaced so that they can dry off. Find a frost free place out of direct sunlight to do this. Once externally dry, (approx. one week) brush off any excess soil. I would recommend dusting your Dahlia tubers with sulphur powder to guard against rot
Store tubers in a clean ventilated wooden or plastic box. Space them evenly apart and cover them with a moist potting compost, peat moss or vermiculite. Do not cover. Place the box in a dry, frost-free place until Spring. Check them periodically over the winter and remove any tubers showing signs of disease or rot.