Dahlias


 

The modern Dahlia.



Today the Dahlia is defined as a half hardy tuberous, herbaceous perennial, and is a member of the compositae species, which also includes the Chrysanthemum, Helianthus (Sunflower), and Zinnia.

They are classed as dicotyledons, of which there at least 20 species, many of which have now been hybridised to give the modern garden dahlia.

Trelyn Rhianne

Origins.


Dahlias are native to the mountain regions of Mexico and Guatemala, where they were first cultivated by the ancient Aztecs who ruled this region.

During the 16th century the Spanish conquistadors arrived with their botanists, whose job it was to bring back plants from the New World for Spain.

These botanists discovered what we today call the Tree Dahlia, (D. imperialis)

These Tree Dahlias grew to over 6 metres in height (20+ft) and had hollow stems topped with open centered single blooms.


These hollow stems were often used to carry water, hence the Aztec name for the dahlia; "Acocotli" or water-cane.

Tree formation
The hollow stem
In flower

Development.


In the beginning; Dahlia seeds and tubers were distributed throughout Western Europe from stock grown at the Royal Botanical Gardens in Madrid, Spain.

The tubers of these plants were used as a substitute for potatoes but they never quite caught on.

Hybridization work in Europe began at the beginning of the 18th century.

Initially this work produced the first fully double forms, along with many new color combinations.

Potato like tubers

Characteristics.


The hybrids commonly grown as garden plants provide brightly coloured displays in most hues, (except blue) from midsummer to the first frosts!

This attribute makes them the ideal plants for summer displays in containers and traditional beds.

The shrubby growth ranges in height from 300 mm (12")to 2400 mm (8ft) subject to variety.

The pinnate shaped leaves are usually mid to dark green in colour although a few varieties produce bronze coloured foliage.

Collection of Dahlias

The flower heads can range in size from 50 mm to 300 mm in diameter (2"-12")

The majority of dahlia species do not produce scented flowers, and like most other species that do not produce scented flowers, they do not attract pollinating insects.

They can be grown in various types of soil, providing it is fertile and well drained.

A pH of around 6.6-7.0 is ideal.

If grown for exhibition or for cut flowers, they are best planted in rows in specially prepared beds.


Classification


Dahlia types in the UK have been classified into groups and sizes by The National Dahlia Society (NDS) and are as follows;



Group 1 - Single-flowered Dahlias


The bloom has a single ring of florets around a central disc.

The outer florets may vary in number from eight upwards, they may overlap, but must not assume double formation.

They should be equal in shape, size and formation and should radiate evenly and regularly away from the central disc in a single flat plane.

The outer edges of these florets may be rounded or pointed.

Volkskanzler

Group 2 - Anemone-flowered Dahlias


This group has one or more outer rings of generally flattened ray florets surrounding a dense group of tubular florets, and shows no disc in the centre.

The outer ray florets should be equal in shape, size and formation flat, and regularly arranged around the central florets.

The blooms should be poised at an angle of 45 degrees on a stem which should be straight and proportionate to the size of the bloom.

Paso Doble

Group 3 - Collerette Dahlias


The outer florets of Collerette dahlias may vary in number from eight upwards, they may overlap, but must not assume double formation.

They should be equal in shape, size and formation and should radiate evenly and regularly away from the central disc in a single flat plane.

The outer edges of these florets may be rounded or pointed.

The inner florets or collar of Collerettes should be uniform in size.

They should be symetrical and not less than one third of the length of the outer florets, even in colour and formation.

The central disc should be flat and circular, and should not contain more than two rows of pollen-bearing stamens.

The blooms should be poised at an angle of 45 degrees on a stem l be straight and proportionate to the size of the bloom.


Birkenshaw Garden Friends
Claire de Lune
Hootenanny
Teesbrooke Audrey
Anne Brekenfelder


Group 4 - Waterlily Dahlias


A waterlily dahlia should be fully double, and the face view should be circular in outline and regular in arrangement.

It should have a firm, circular, closed centre which should be proportionate to the size of the bloom.

The depth should be approximately half the diameter of the bloom.

Waterlily dahlias should be poised at an angle of not less than 45 degrees to the stem, and the stem should be straight and of a length and thickness proportionate to the size of the bloom.


Adringham
Bracken Laureli
Sascha
Tahatari Ruby
Shorty Bridge

Group 4c

This category has medium sized flowers which are usually between 152mm and 203 mm (6"-8")in diameter.

Group 4d

Small sized flowers which are usually between 102mm and 152mm (4"-6")in diameter.

Group 4e

Miniature sized flowers not usually exceeding 102mm (4")in diameter.


Group 5 - Decorative Dahlias


The ideal bloom of a double-flowered dahlia should be symmetrical in all respects, and the outline should be perfectly circular.

It should have a firm, circular, closed centre which should be proportionate to the size of the flower.

The bloom should be "full", i.e. it should, without overcrowding, have sufficient florets to prevent gaps in formation and outline, and to give depth to the bloom which should be approximately two-thirds, or more, of the diameter.

The flowers should be poised at an angle of not less than 45 degrees to the stem.

The stem should be straight and of a length and thickness proportionate to the size of the bloom.

The general formation of blooms and their florets should correspond to the standards laid down for that particular group of dahlia.


Group 5a - Giant


This group have giant sized flowers which are usually over 254mm (10")in diameter.

Bryn Terfel
Cream Alvas
Fairway Spur
SirAlf Ramsey

Group 5b - Large


Have large sized flowers which are usually between 203mm and 254 mm (8"-10")in diameter.

 
Elma E
Kenora Valentine

Group 5c - Medium


Have medium sized flowers which are usually between 152mm and 203 mm (6"-8")in diameter.

 
Brian R
Hillcrest Kismet
Neal Gilson
Trengrove Millenium

Group 5d - Small


Have smaller sized flowers which are usually between 102mm and 152 mm (4"-6")in diameter.

 
Primrose Diane
Ruskin Diane
Rycroft Brenda
Winholme Diane

Group 5e - Miniature


Have miniature sized flowers not usually exceeding 102mm (4") in diameter.

 
Andrea Lawson
Jubilee Boy
Rycroft Jan
John Hill


Group 6 - Ball Dahlias


All ball dahlias should be ball-shaped, but the tendency towards flatness on the face of the larger cultivars may be tolerated and a reasonable latitude may be allowed.

The florets should be symmetrically arranged and should dress back to the stem to complete the ball shape of the bloom.

The florets should be compact and dense at the centre.

The flowers should be poised at an angle of not less than 45 degrees to the stem.

The stems should be straight and of a length and thickness proportionate to the size of the bloom.


Group 6a


Has small sized flowers which are usually between 102mm and 152 mm (4"-6")in diameter.

 
Blyton Softer Gleam
Blyton Bright Eyes
David Digweed
Westerton Folly

Group 6b


This group has miniature sized flowers that are usually between 52mm and 102mm (2"-4") in diameter.

 
Jomanda
Marys Jomanda
Megan Dean


Group 7 - Pompon Dahlias


A Pompon dahlia should have fully double spherical blooms of miniature size,(usually not exceeding 52mm (2") in diameter)

The florets should be involute for the whole of their length (longitudinal axis). , be evenly, and symmetrically arranged throughout the bloom and should dress back fully to the stem.

Blooms should face upwards on a straight, firm stem.


Gurtla Twilight
Ivor's Rhonda
Moorplace
Pop Willow
Rhonda
Willow's Violet


Group 8: Cactus Dahlias


The ideal bloom of a cactus dahlia should be symmetrical in all respects, and the outline should be perfectly circular.

It should have a firm, circular, closed centre which should be proportionate to the size of the flower.

The bloom should be "full", i.e. it should, without overcrowding, have sufficient florets to prevent gaps in formation and outline, and to give depth to the bloom which should be approximately two-thirds, or more, of the diameter.

The ray florets are usually pointed, the majority narrow and revolute for 50% or more of their length (longitudinal axis) and either straight or incurving.

The flowers should be poised at an angle of not less than 45 degrees to the stem.

The stem should be straight and of a length and thickness proportionate to the size of the bloom.

The general formation of blooms and their florets should correspond to the standards laid down for that particular group of dahlia.


Group 8a


Have giant sized flowers which are usually over 254mm (10") in diameter.

Polar Sight

Group 8b


Have large sized flowers which are usually between 203mm and 254 mm (8"-10")in diameter.

Light Music

Group 8c


Have medium sized flowers which are usually between 152mm and 203 mm (6"-8")in diameter.

Amber Banker

Group 8d


Have small sized flowers which are usually between 102mm and 152 mm (4"-6")in diameter.

 
Kelsae Carla
Kiwi Gloria
Weston Miss
Trelyn Kiwi

Group 8e


Have miniature sized flowers not usually exceeding 102mm (4")in diameter.

Weston Spanish Dancer


Group 9 - Semi-Cactus Dahlias


The ideal bloom of a semi-cactus dahlia should be symmetrical in all respects, and the outline should be perfectly circular.

It should have a firm, circular, closed centre which should be proportionate to the size of the flower.

The bloom should be "full", i.e. it should, without overcrowding, have sufficient florets to prevent gaps in formation and outline, and to give depth to the bloom which should be approximately two-thirds, or more, of the diameter.

The ray florets are usually pointed, and revolute for more than 25% of their length and less than 50% of their length (longitudinal axis), broad at base and either straight or incurving.

The flowers should be poised at an angle of not less than 45 degrees to the stem.

The stem should be straight and of a length and thickness proportionate to the size of the bloom.

The general formation of blooms and their florets should correspond to the standards laid down for that particular group of dahlia.


Group 9a


Have giant sized flowers which are usually over 254mm (10")in diameter.

Pink Jupiter

Group 9b


Have large sized flowers which are usually between 203mm and 254 mm (8"-10")in diameter.

Kenora Challenger

Group 9c


Have medium sized flowers which are usually between 152mm and 203 mm (6"-8")in diameter.

 
Grenidor Pastelle
Pat Maric
Stalleen Contessa
Trelyn Rhianne

Group 9d

Have small sized flowers which are usually between 102mm and 152 mm (4"-6")in diameter.

Hayley Jane

Group 9e


Have miniature sized flowers not usually exceeding 102mm (4")in diameter.

Mini Red


Group 10 - Miscellaneous Dahlias


This group is to cover for dahlias that do not fall into any of the foregoing groups, e.g. Star and Orchid-flowered dahlias.

Blooms in the exhibit shall be similar in size and formation.

Blooms should be poised at an angle of not less than 45 degrees on a stem which should be straight and proportionate to the size of the bloom.


Honka
Juuls Allstar
Llangothlan Junction
Marie Schnugg
Tahoma Hope


Fimbriated Dahlias


A fimbriated dahlia should be a fully double bloom.

The petals should be split or notched, uniformly throughout the bloom, to create a fringed overall effect.

The petals may be flat, involute, revolute, straight, incurving or twisted.

Marlene Joy


Cut Flowers

It is important that blooms be presented on firm wiry stems and with proportionate foliage that enhances the blooms.

Stems which are bent, weak, short jointed or out of proportion to the blooms comprise a serious fault.

Bright attractive colour and blends should be regarded as meritorious.




Flower Sizes


For exhibition purposes Judges use a set of NDS regulation rings to determine the diameter of each group.

To comply these rings when passed over the blooms must not touch any petals.

To do so would render the exhibit as N.A.S (not as schedule) and it would be disqualified!

Set of Regulation Rings


Dual Classification

Some varieties of dahlias can have a dual classification.

These are varieties that are borderline in size or form, and as a result of this, they can exhibited in more than one size group.


Dahlia cultivation


Week 2-3:


Check over dormant Dahlia tubers, remove any rotten parts, and dust with sulphur powder.


Week 4-6:


Set saved tubers on the top of boxes/trays filled with a 50-50 mix of compost and sharp sand.

Water in with a mix of fungicide* and water, mixed to manufactures instructions.

* Use of a fungicide is optional!

Saved Tubers


Place containers on a hot bed set to give a bottom heat of 18°C (65°F) and a surrounding air temperature circa 10°C (50°F) to encourage basal growth for cuttings.

Normally, it takes around two to three weeks for basal growth to appear, and a further four or five weeks, to produce shoots that are suitable for cuttings.

Tubers on Hotbed

Week 12 / 13:


Take 50-60mm long cuttings if required.

Remove bottom leaves and insert 30-40mm apart in a mixture of 50-50 (by volume) peat and grit sand (dipping cutting in rooting powder/ liquid is optional)

On completion; water cuttings in, with a fungicide* solution.

Mist spray (daily) with a fungicide* solution to prevent dehydration and damping off

* Use of a fungicide is optional!


Sever cutting from tuber
Cut cutting below node
Prepared Cutting
Insert cutting into compost

Week 17 >>:


Depending upon available light, the cuttings should take around two to three weeks to root.

When the tip of the cutting looks a healthy shade of green suggesting that it has rooted, prick out into 70mm pots filled with potting compost.

Place pots in a well lit position but out of direct sunlight.


Week 18:


Place cuttings in a cold frame to harden off.

If more stock is required lift tubers from trays and divide them into pieces ensuring that each piece has at least one eye (growing point) on it.

Allow the wounds on the divisions to cauterise (dry) before planting them out.

Divided Tuber

Week 19 / 20:


If not already done, prepare beds for planting out by digging in manure or garden compost.

Leave the bed roughly dug so that frost can break up the soil.

Check soil pH and adjust if required, aim for 6.5-7.0


A few days prior to planting out rake in a general fertilizer at 125g/sq m (4oz/sq yd).

Bed Fertilised
Rake in Fertiliser

Week 22 / 23:


When all fear of late frost has passed, remove the plants from their pots and plant out in pre-prepared beds and borders.

Set them 600mm (24”) apart supporting each with a 1200mm (4’) cane/stake.

To avoid any damage to the roots, position the supports in the hole prior to planting.

Tie the plant loosely to the support at regular intervals as the plant grows taller.

Plants in the Bed

Pot up any surplus plants into 125mm (5") pots and grow on as pot tubers in the cold frame.

These will form the basis for the following year’s cuttings.

Dormant tubers may be planted directly, about six weeks before the last frosts, whereas plants in leaf should not be planted until all danger of frost has passed.

If the new shoots emerge above ground level from early planted tubers and there is still a risk of frost, cover them with agro-fleece for protection.


Week 25/27:


With plants grown for general use, remove the growing tip of each plant to encourage bushier growth.

If growing for exhibition, limit the number of shoots on each plant to around three or four (subject to variety)

For example giants should only have two or three shoots whereas miniatures can usually withstand six to eight shoots.

Basically it all amounts to the size of the blooms required.

To produce high-quality blooms, disbud each shoot to one bud.

Dahlias require copious amounts of water during their growing season.


Week 26/28:


As flower buds develop, extra potash in the liquid fertilizer will promote strong stems and good flower colour.

It can be advantageous at this time to mulch the beds with straw, grass cuttings or spent mushroom compost to conserve moisture.

Do not place the mulch too close to the base of the plant as this may encourage stem rot.

If using composted grass cuttings as mulch ensure that they have not been treated with a selective weedkiller.

Protect your flowers from earwigs;

Insert bamboo canes alongside your plants, these can double up as plant support.

Place an upturned flowerpot/s filled with newspaper or straw on top of the cane/s, in the hope that earwigs will hide inside these pots, then daily empty out the pots and squash any earwigs that you find.

Earwig

Week 29 / 30:


Give plants a high potash feed to stiffen the stems and enhance the colour of the blooms.

Thin out the number of branches on each plant and remove secondary buds. (see note above)

This will give better quality long stemmed flowers.

Tie the remaining branches to sturdy stakes set three to a plant.


Week 30-32:


If the plan is to exhibit, it is beneficial to erect some form of canopy over the blooms, to prevent them getting damaged by the weather.


Week 40 / 44:


Lift out tubers once the foliage has been blackened by the first frost.

In the event there has been no frosts to blacken the foliage, leave the plants in place and lift from say late October to mid-November.

Place them upside down for a few weeks to ensure that no moisture remains in the stems and leaves.

Drilling a hole through the base of the stem with a screwdriver or similar, will enable any water lodged at the point where the base of the stem meets the tuber to drain away.

This will help to prevent moisture building up that could cause rot.

Remember to label named varieties!

Do this by pushing a length of plastic-coated wire through the hole in the plant label and tying it to, or through the tuber.

When the tubers are quite dry, remove the dried soil and trim off the thin water roots and any damaged parts of the tuber and store them in a cool frost free area until required.

Check periodically for signs of decay, remove any rot that may appear.

Boxed up ready for
winter storage


Bedding Dahlias


Bedding dahlias, sometimes known as Dwarf bedding dahlias will thrive in most types of well-drained soil, that has been enriched with well rotted manure or compost.

These types are generally grown either by taking cuttings or dividing the tubers of named cultivars.

Alternatively, they can be grown annually from seed.


A selection of different coloured Bedding Dahlias

They grow to around 750mm (30") tall and should be planted out 400mm (16") apart in a sheltered sunny border.

The double, semi- double or single flowers appear from late July to November or the first frosts.

The flowers are generally around 75mm (3") in diameter and come in many pastel shades.

Regularly water throughout the summer months, and feed weekly with a high potash feed from bud formation.

Aftercare for bedding dahlias is basically the same as for disbud dahlias in terms of location, feeding and watering.


Week 2-3:


Check over dormant Dahlia tubers, remove any rotten parts, and dust with sulphur powder.


Week 5-6:


Set up saved tubers on the top of boxes/trays filled with a 50-50 mix of compost and sharp sand.

Water in with a mix of fungicide* and water, mixed to manufactures instructions.

* Use of a fungicide is optional!

Place containers on a hot bed set to give a bottom heat of 18°C (65°F) and a surrounding air temperature of 10°C (50°F) to encourage basal growth for cuttings.

Normally, it takes around two to three weeks for basal growth to appear and a further four or five weeks to produce shoots that are suitable for cuttings.

Signs of Basal Growth

Week 11:


Sow seed in pots or trays of seed compost and germinate at 20°C (68°F)

Germination should take around six or seven days.


Week 12 onwards:


Take 50-60mm long cuttings if required.

Remove bottom leaves and insert 30-40mm apart in a mixture of 50-50 (by volume) peat and grit sand (dipping cutting in rooting powder/liquid is optional)

On completion, water cuttings in with a fungicide solution*.

Mist spray (daily) with a fungicide* solution to prevent dehydration and damping off.

* Use of a fungicide is optional!

Sever cutting from tuber
Cut cutting below node
Prepared Cutting
Insert cutting into compost

Week 13-14:


When seedlings are large enough to handle, prick out into 75mm (3") pots of potting compost.

Grow on at a minimum temperature of 10°C (50°F) for two or three weeks then place them in a frost free coldframe to harden off until planting out time.


Week 15 onwards:


Depending upon available light, the cuttings should take around two to three weeks to root.

When the tip of the cutting looks a healthy shade of green suggesting that it has rooted, prick out into 70mm pots filled with potting compost.

Place pots in a well lit position but out of direct sunlight.


Week 18:


Place cuttings in a cold frame to harden off.

If more stock is required lift tubers from trays and divide them into pieces ensuring that each piece has at least one 'eye' (growing point) on it.

Allow the wounds on the divisions to cauterise (dry) before planting them out.

Divided Tuber

Week 22:


Plant out 400mm (16") apart when all fear of late frost has passed.

In exposed areas insert a 1200mm (48") cane in the planting hole prior to planting to avoid damaging the forming tuber if done at a later date.

Planted out in Border

Week 28:


Protect your flowers from earwigs.

Insert bamboo canes alongside your plants, these can double up as plant support.

Place an upturned flowerpot/s filled with newspaper or straw on top of the cane/s, in the hope that earwigs will hide inside these pots, the daily empty out the pots and squash any earwigs that you find.

Earwig

Week 30/32:


Give plants a high potash feed to stiffen the stems and enhance the colour of the blooms.

Thin out the number of branches on each plant and remove secondary buds. This will give better quality long stemmed flowers.

Tie the remaining branches to sturdy stakes set three to a plant.


Week 40 onwards:


Lift out tubers once the foliage has been blackened by the first frost, but if this does not happen, lift from late October to mid-November.

Remember to label varieties you would like to save for next year.

Do this by pushing a length of plastic-coated wire through the hole in the plant label and tying it to, or through the tuber.

Drilling a hole through the base of the stem with a screwdriver or similar will enable any water lodged at the point where the base of the stem meets the tuber to drain away.

This will help to prevent moisture building up that could cause rot.

When the tubers are quite dry, remove the dried soil and trim off the thin water roots and any damaged parts of the tuber and store them in a cool frost free area until required.

Check periodically for signs of decay, remove any rot that may appear.


Exhibiting

Judging


The judging of dahlias is not and cannot be an exact science, however the reading of The National Dahlia Societies Classified Directory and Judging Rules is a good starting point to determine what is required.

This is a fairly comprehensive document and if used in full may be too elaborate for the organisation running the show, so it is recommended that such organisations produce a ‘Show Schedule’ that includes any specific rules they may want to apply.

This would be particularly relevant at say a small 'village show'

The production of such a schedule will ensure that the exhibitors know what is expected of them and the judges can judge the exhibits accordingly.


Staging of Exhibits


An exhibit of dahlias should be arranged so that all the blooms face in the same direction, are clear of each other, and staged so that a pleasant and balanced exhibit is achieved.

All blooms should be staged with some dahlia foliage, preferably on the stem.

The foliage should be clean, healthy and undamaged.

It is recommended that names of all cultivars, in an exhibit are clearly and correctly stated.

An exception to this is varieties grown from seed.

The use of blocks under vases to create a tiered effect is permitted.


Various Staging Combinations


One vase of Five Pompons
One vase of Five Small Cactus
Three Giants (one bloom per vase)
One vase of Five Miniature Ball Dahlias
One vase of Five Miniature Ball Dahlias

Twelve Medium Semi-Cactus
3 Blooms per Vase
Two vases of Three Large Semi-Cactus
Three vases of Three Medium Semi-Cactus
Two vases of Five Small Cactus
Multi vase class
Five distinct groups

 
Silver Medal - Bronze Medal
 

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