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Dahlia

Posted on 18th June 2015

Dahlia are regaining popularity and are not difficult to look after and propagate if you understand a few basic principles.

Dahlia are classed as tender perennials which means that although they live for several to many years they are not adapted to cold climates and often do not survive the winters outdoors in the UK. Therefore, like many other tender perennials we need to ‘overwinter’ them in a frost free place.

Dahlia can be grown from seed if you start them off early in the year in a heated greenhouse but to ensure flowers in the first year it is best to buy them as dry crowns/tubers or growing plants in the early spring. If you buy the crowns you should pot them up straight away with the tubers sitting just below the surface of the compost. Grow them on until they have produced a nice bushy plant and they can be hardened off at the end of May and plant out either into summer containers, bedding schemes or use them to fill gaps in mixed borders to add vibrancy and colour in the late summer.

They need a fairly fertile soil or potting mix and if dead headed regularly should continue flowering until the first frosts. Do not worry too much if they catch an early frost, it is recommended that they are left out for the first frosts to catch the leaves and stems, this will ensure that they are triggered into the start of dormancy. Although the leaves and stems may become blackened by the frost, the tubers will be unaffected by early, light frosts. You should lift the whole plant after the first frost and cut off the top growth. Clean excessive soil or compost from the roots and tubers and leave them out in an airy, frost free place for a couple of weeks to dry out a bit. They can then be stored in dryish compost or sand in a frost free place for the winter.

In late March they can be potted up again and you can begin watering them to prepare them for the next growing season. At this stage you can split the tubers to propagate or wait for the new shoots to reach about 10cm long and you can take softwood cuttings from them at this stage. Only take one or two cuttings from each plant.