The Dahlia - our expert Martin Horne
| Published: 6th June 2007 18:23 |
The Dahlia - our expert Martin Horne
The Dahlia
This half-hardy tuberous plant was named after Dr. Anders Dahl, a Swedish botanist, although it could very easily have been called ‘Georgina', after the botanist Johann Georgi. In fact, in some places, until fairly recently, some people still referred to the plant as the ‘Mexican georgina'.
Dahlias originated in Mexico and were brought back to Europe by Spanish invaders but it took several years before they really became established as a favourite plant. Nowadays, the Dahlia features strongly in horticultural shows and as a sturdy-stemmed cut flower.
Husbandry of the Dahlia
As mentioned above, the Dahlia is a tuberous plant, so, to provide good, strong plants, the tubers need to be planted in fertile, well-drained soil in spring, ensuring that the plant is protected from late frosts. Many people, especially those hoping to exhibit, dig a trench and add organic matter to develop a good, healthy structure for the soil.
As an alternative to direct planting, the tubers could be planted initially into pots as large as two litres in sheltered conditions such as a frost-free greenhouse, then transplanted when conditions allow.
Dahlias thrive in the sun but are frost and damp-sensitive through winter.
Dahlias may be propagated in a number of ways but the most popular is by vegetative means - that is from parts of the plant. Dormant tubers may be cut carefully, using a clean, sterile knife or, alternatively, take cuttings from developing young stems. Both of these means of propagation ensure that the resultant new plants grow true in shape, form and flower colour to the parent plant.
Another way of propagating dahlia plants is from seed, known as sexual reproduction. Seeds may be saved from parent plants or purchased from seed merchants. Sow seeds by the half-hardy method in early to mid-spring, pricking-out, potting-up, hardening-off (weaning and preparing for outside planting). The possible disadvantage of propagating by this means is that plants are not guaranteed to grow true to type or colour but it is an inexpensive way of producing new plants.
As mentioned earlier, dahlias, especially those of the cactus and decorative varieties make excellent cut flowers. Stems of dahlias are hollow, so, when harvesting the flowers for display, it is best to cut them by taking a vase filled with fresh water to the plant. Cut the stems with a sharp knife (not scissors as they ‘squeeze' the stem). Make a diagonal cut in the stem before placing the plant into the water. Why a diagonal cut? This allows for water to be taken up int the hollow stems should the stems reach the bottom of the vase.
At the first major frosts, the flowers and foliage are blackened and it is time to look at ways of preserving tubers.
Some people leave the tubers of dahlias in the ground but I personally am wary of this, as the tubers are at risk from rotting in winter damp. The water resting on the tubers may be more of a hazard to tubers than winter frosts and snow.
I would suggest, therefore, that tubers should be carefully lifted from the ground, turned upside down for about a week to allow for all excess moisture in the stems to drain away. Then store the tubers in a frost-free place such as a shed or garage, using peat, sand, vermiculite, perlite or similar media over winter before starting the growing process again in spring.
Dahlias give so much pleasure and that pleasure can be enhanced with a little care. Good luck with your growing!
Martin Horne
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