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Delightfully Easy Dahlia

This beautiful flower is actually native to the highlands of Mexico and was grown by the Aztecs in the region near the present site of Mexico City.

This beautiful flower is actually native to the highlands of Mexico and was grown by the Aztecs in the region near the present site of Mexico City.

Dahlia flowers are popular landscape plants known for their wide range of colours, heights and forms. These versatile flowers are ideal for novice gardeners.

In relation to other genera, the dahlia is a fairly new addition to the garden scene. Baron Alexander von Humboldt, a naturalist and statesman, brought some of the first dahlia seeds from their native Mexico to Germany as recently as 1805. There is also a record of dahlias flowering only a few years previously in 1789 in the botanical gardens in Madrid. All dahlias were reproduced from seed until about 1820 when it was discovered that they could be grown successfully from cuttings. The first double‑flowering, pure white dahlia was hybridized in Holland in 1821 and the first cactus dahlia a mere 100 years ago in 1872.

Dahlias are tender, tuberous rooted plants, varying in height from a few centimetres to about two metres, and with flowers from button size to dinner plate size, depending on the variety and type of culture. Dahlias come in all colours and combinations of colours, and those with the largest blooms are usually the result of special forcing and pruning techniques used for show purposes. These show flowers are generally found on tall single stemmed plants with the stems sometimes as thick as broom sticks.


The most popular dahlia types are:

DECORATIVE with fully double flowers having the margins of florets slightly incurved and flattened towards tips which may be pointed or rounded.

CACTUS with flower heads fully double but the margins of the flowers revolute for not less than three‑quarters of their length and the central florets form a filbert-shaped group.

SEMI-CACTUS which is midway between decorative and cactus with the florets broad at the base, and the margins revolute towards the tips, slightly twisted for about half their length.

POMPOM in which the flowers are also fully double but the flower head is completely rounded and not more than five centimetres across.

Dahlias form a valuable addition to the summer garden with their colourful and profuse blooms. They may be grown in a herbaceous border, but they are perhaps most valuable in beds by themselves, where their varying colours and heights can be shown to greatest effect.

To promote a compact, bushy growing habit, with more flowers, pinch back the new growth when your dahlia is about 30cm high. If your goal is to produce massive sized flowers, remove all of the side buds at the end of each branch throughout the growing season. If you want your Dahlia to provide a continuous, extended flower show, you will need to remove the spent buds promptly.

Dahlias are produced in nurseries by placing selected tubers in heated trenches and taking cuttings as the sprouts emerge from the tuber which will produce about 15 sprouts over a period of some months. The cut end of the sprout is dipped in a hormone solution and the sprout is then placed in a tray of sand. When the cutting has produced the small beginnings of a tuber at its base it is planted out in a field where it will produce a fully fledged tuber before the onset of winter.

Although there is a choice between buying locally grown or imported dahlias in South Africa, it is best to purchase locally grown tubers as they are fresh and have been adapted to suit our climate and seasonal changes. South African tubers are lifted in May from the nursery beds and planted by the home gardener after the threat of frost has passed in early September, thus assuring them of the natural four months rest period, as opposed to the year which has passed between the lifting and planting of imported tubers, due to their different seasons.

Dahlias are gross feeders and need a deep rich soil with plenty of compost and well‑rotted manure dug in. A sunny position is essential, and one should wait until the weather starts to warm up and all danger of frost has passed before planting the tubers with their necks a few centimetres below the soil surface. Large varieties should be spaced about 60cm apart while the smaller or dwarf ones can be planted 35cm apart.

The soil should never be allowed to dry out as this will prevent flowering, so mulching is essential, and if you are in an area suffering from lack of water, plant each dahlia so that the soil above it forms a slight depression to prevent run‑off when using your precious water. Once the dahlias have sprouted above the surface of the soil, it is essential that they be staked, and if good blooms are wanted, pruning and disbudding should be practised as necessary.


Keep your dahlias weed-free. Weeds compete for water, nutrients, and light, and often harbor harmful insects and diseases. Mulches are effective in controlling weeds. Organic mulches like straw and hay keep the soil cool and conserve moisture. They are particularly desirable in the heat of summer.

Dahlias are susceptible to several diseases, the most common of which are in the virus group, although this is less of a problem in healthy, large tubers. Powdery mildew is commonly found where plants are massed closely together for effect, thus causing moist conditions within the foliage. Spray with a fungicide to eradicate this.

Aphids and cutworms are the principal pests which attack dahlias, and these can be combated with insecticide and cutworm bait. The tender new growth of a Dahlia is a favourite entree of slugs and snails. Take the necessary precautions to protect your plants


The high point of growing dahlias is enjoying the flowers. They may appear any time in summer, depending upon the varieties and types you’re growing. To use dahlias as cut flowers, cut the blossoms when they are fully open. Use sharp shears or a knife to cut a long enough stem for the use intended. Plunge the cut ends into warm water immediately. When you’re ready to arrange the flowers, cut off about 4mm of the stem base and place the stems in warm water. Be sure to use a sharp knife or shears. Using floral preservatives or changing the water every 2–3 days will increase the life of cut flowers. Another useful technique is to place the basal 25mm of each stem in boiling water for 1 minute while shielding the leaves and upper stem and flowers from the steam and heat.


To store your precious tubers for the next growing season, make sure the plants are well fed throughout the growing period so that they can store up food in the tubers. As soon as the plants start yellowing usually in mid-autumn — cut the plants to within a few centimetres of the soil surface and lift the tubers. Rinse surplus mud off the tubers, let them dry off in a cool spot, and then place them in boxes, buried in clean river sand or wood shavings. Be sure to label each box with the type, colour and so on of the tubers stored in it. The boxes should be left in a cool dry place in your shed or garage until spring when once again it is time to plant them.