Dahlia “Magenta Star” growing at Great Dixter
Delighted to say that Siew Lee Vorley (below), Assistant Head Gardener at Great Dixter has agreed to write a guest blog about potting up Dahlias.
It’s great to have expert advice, so read on ….
Dahlias look frankly obscene when they have no clothes and none more so now, when they will have spent the past 4 months in the dark and cold. It is time take them out of storage and breathe life into the poor shrivelled specimens. Assuming your excuse of a dahlia clump still has some integrity left (which is to say it is neither a rotten pile of mush or a hollow skeleton, but is still hard, even if some of the tubers are hanging on by the skin of their teeth to the base) all that needs to be done is cut off all the rotten bits, pot them up into good compost, water and place them in a warm place with good light and let the miracle of growth do its thing.
As a general rule, the size of the pot should comfortably accommodate the clump, and no more. Pot on when the plants outgrow their pots. This is also a good time to split the tubers to increase your stock, assuming you have good-sized clumps to begin with. It is crucial to remember, when splitting dahlias that every piece has growing point and tubers (or a tuber) attached. These buds are located between the neck and the tubers, at the base of the clump (see picture above). A clean, vertical cut can be made right in the middle of the base or even through an old existing stem if necessary. Individual clumps can then be potted up.
Another way to increase your stock is to take basal cuttings. You will find a few weeks on new shoots beginning to appear. Take 2.5 inch cuttings, about the thickness of a barbeque skewer. Cuttings should root in about 2 weeks. These can then be grown on, but depending on variety may not make flowering plants. To do that, process really needs to be started in February. Also, to ensure the parent clump retains enough energy for a decent display later on, stop taking cuttings after late April.
Dahlias have a good appetite for warmth, light, food and water. Your beauties should be ready for the open world by June onwards. Prepare the ground well by digging in plenty of organic matter, supplemented with fertilisers such as Growmore if need be. Slugs like juvenile dahlia foliage, so protect them when they are young. Dahlias, especially the tall elegant ones will need staking, but that, is a story for another day.
Out of my shed 