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How to Grow Dahlias

By Edited Jun 25, 2016 0 4

Grow Your Own Dahlia Wedding Bouquet

The dahlia is easy to grow and provides a great mass of blooms over a long period in late summer and autumn. Dahlias are popular in bouquets, especially wedding bouquets.

Dahlias range from low-growing border plants of a foot high to elegant background specimens up to 6 feet in height. Flowers range from 2 to 12 inches in diameter and include a variety of shapes and sizes. Colours include white, yellow, orange, pink, purple, red and scarlet. Flowers may be striped or tipped with a second colour. There are thousands of cultivated varieties that have been hybridised over many years.

Vase of Dahlias

The dahlia was named in honour of Dr Andreas Dahl, a Swedish botanist. It is endemic to Mexico but found its way to Madrid in 1789. Today there is a tremendous array of variety in both colour and form.

Dahlias are classified according to the arrangement of the petals and the shape of the flower. Even within a classification there may be subdivisions.

Single-flowering varieties have blooms with one row of petals, a diameter of 4 inches or less and generally grow to a maximum of 3 feet high. Within the single-flowered varieties are: singles (a ring of evenly spaced petals), orchid-flowering (florets curl along the edges), anemones (have an extra ring of petals) and collarettes.

Single Dahlia

Single Dahlia (above)

Double-flowering types are taller, have multiple rows of petals and large flowers. Included in the double-flowering types are cactus dahlias (rather tubular shaped petals curve backwards over ½ their length), semi-cactus (similar but broad-based petals curving for less than half their length) and incurved cactus cultivars (strong curling of the petals towards the centre of the flower).

Formal decorative dahlias have petals that are broad, pointed or rounded and arranged regularly curving back toward the stem.

Cactus Dalhia

Cactus dahlia (above)

Informal decorative dahlias have long, often twisted petals which are irregularly arranged. Ball dahlias are ball shaped or slightly flattened, with blunt or rounded quilled petals. Flowers around 3 ½ inches in diameter qualify the plant as a ball dahlia, similar plants with flowers less than 2 inches in diameter are known as pompon dahlias.

Dahlias need a sunny position with well-drained soil that has an open friable structure. If your soil is too sandy, you need to add organic matter in the form of compost, leaf mould or peat moss. The ideal pH is between 6.2 and 6.5. Animal manure can be added too but don't add too much as it will result in luxurious leaves but few flowers. If the soil is acid add some lime but no more than ½ a cup per square metre on heavy soils. A light scattering of mixed fertiliser will also be of benefit.

Collarette Dahlia(52934)

Collarette Dahlia (above)

Dahlias are tubers and generally hardy in USDA zones 7-11. It is usual to plant them each spring. They are then cut back and dug up or 'lifted' each autumn after the first heavy frost.

Dahlias can be grown from seeds, cuttings, tuberous roots or purchased as transplants. Don't plant tubers until all danger of frost has passed. The soil temperature needs to be between 58 and 60oF. If the soil is excessively wet, the tubers will rot.

Orchid Dahlia

Orchid-type Dahlia (above)

Prepare a hole 12 inches in diameter and 12 inches deep. To the soil you've removed from the hole, add a spadeful of compost plus a handful of bone meal and a little Dolomite lime. Half fill the hole with the soil mix and place the tuber in the hole with the eye pointing upward. If you are growing a tall variety, add a stake at this point. This will prevent the tuber being pierced if it is added later. Cover the tuber with another two inches of soil and water thoroughly. Once the shoots emerge, add more soil mix from time to time till the hole is full of soil.

When the plant is tall enough, tie it to the stake. Staking is necessary for the taller varieties as they are rather brittle and can snap quite easily. Old pantihose or stockings are good ties as they will not cut into the plant. Continue to add more ties as the plants grow.

Semi-Cactus Dahlia

Semi-cactus Dahlia (above)

When the buds appear, feed soluble fertilisers every 10 to 14 days. This will help promote large blooms and will prolong flowering. Dahlias are heavy feeders and will require regular fertilising while they are flowering.

Although dahlia seeds can be sown in spring or early summer, they may not grow true to type. This is because dahlias are hybrids. Seeds can be started as bedding plants then treated as annuals. In warm areas, they can be sown in pots and transplanted like any other seedlings. Dahlias grown as seeds will form tubers which can be lifted and replanted but because the plants grow so easily from seed, many people think it is easiest to throw out the old plants and start with new seeds. In warm regions, seeds can be sown directly into the garden. Otherwise start them indoors 6 to 8 week prior to transplanting outdoors.

Anemone Dahlia

Anemone Dahlia (above)

Tubers should not be lifted until the plants have completely died down which will usually be in early winter. Store the crowns in the shade over winter. In cooler areas, place the tubers in sawdust or vermiculite. Store in a dry area, preferably at a temperature of about 40oF. If you notice the tubers shrivelling, moisten the sawdust or vermiculite and if they are becoming mildewed, treat with a dry fungicide.

As the warm weather begins, the tubers will begin to form 'eyes' or shoots. The tubers can be cut between the shoots leaving some stem tissue and several tubers attached to each piece.

The growing point can be 'stopped' or pinched out when the plant is about a foot high. This will encourage a compact, bushy plant. Disbudding is also practised with the tall-growing dahlias. Removing all the side buds at the end of each branch will result in huge sized flowers.

Water established plants thoroughly and deeply once a week or more frequently if it's very hot. Slugs and snails love the new growth of dahlias so you will need to take adequate precautions against these pests. Tag your plants if you want to identify the varieties for later.

Pompon Dahlia(52946)

Pompon Dahlia (above)

When cutting the blooms for indoor decoration, pick them in the cool of the evening. Dip the stem ends in boiling water for about 30 seconds. Tilt the container a little so the steam does not scald the blossoms. Dahlias make excellent cut flowers lasting up to a week indoors. Change the water daily.

Dahlias are well worth the trouble of growing. Their variety of form and great colours give much pleasure for a satisfyingly long period.



Jul 8, 2011 2:45pm
Awesome article. Dalhias are one of my favorite flowers.
Jul 10, 2011 6:27am
Thanks Lynsuz. I love the pompon flowers. They are just so perfect.
Jul 21, 2011 7:32am
Great post! I have been growing dahlias for quite sometime now. I have a lot of reasons to have them in my garden, but you just showed another 'why' for me to continue doing such--bouquets. Anyhow, you can check out a decent selection of dahlia tubers at http://www.lynchcreekdahlias.com/. Thanks!
Jul 22, 2011 2:59am
Thanks for the comment. They are beautiful plants. I will check out your website shortly. Welcome to IB and I look forward to reading some of your articles in the future.
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