The Gardener's Almanac

Dahlias

CURRENT MOON

For information on what to do in your garden this week!

Location;

Basal growth

Select cutting

Sever cutting

Remove basal leaves

Trim cutting to below node

Trimmed cutting

Cutting ready for rooting

Dahlias make ideal plants for summer display in containers and traditional beds.

They will provide colour in the garden from mid summer to the first frosts!

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.

Dahlia types in the UK have been classified by the National Dahlia Society and are as follows;

Group 1; Single-flowered Dahlias The bloom has a single ring of florets around a central disc.

Group 2; Anemone-flowered Dahlias Have blooms with one or more outer rings of generally flattened ray florets surrounding a dense group of tubular florets, and showing no disc.

Group 3; Collerette Dahlias Have blooms with a single outer ring of generally flat ray florets, which may overlap, with a ring of small florets (the collar) around the central disc.

Group 4; Waterlily Dahlias Have fully double blooms characterised by broad and generally sparse ray florets, which are straight or slightly involute along their length, giving the flower a shallow appearance. The depth should be less than half the diameter of the bloom.

Group 5; Decorative Dahlias Have fully double blooms showing no disc. The ray florets are generally broad and flat and may be involute for no more than 75% of their length (longitudinal axis) or slightly twisted, and usually bluntly pointed.

*Group 6;* Ball Dahlias Have fully double blooms, ball shaped or slightly flattened. The ray florets blunt or rounded at the tips, with margins spirally arranged and involute for at least 75% of the length of the florets.

Group 7; Pompon Dahlias Have fully double spherical blooms of miniature size, with florets involute for the whole of their length (longitudinal axis).

Group 8; Cactus Dahlias Have fully double blooms, 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.

Group 9; Semi-Cactus Dahlias Have fully double blooms 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

Group 10; Miscellaneous Dahlias This group is to cover for dahlias that do not fall into any of the foregoing groups, e.g. Orchid-flowered dahlias.

Slide Show
Various Dahlia pictures from the above categories.

For exhibition purposes; these groups have been sub-divided into different sizes.

Giants; Over 254 mm (10") diameter

Large; should be between 203 mm (8") and 254 mm (10") diameter.

Medium; should be between 152 mm (6") and 203 mm (8") diameter

Small ; should be between 102 mm (4") and 152 mm (6") diameter

Miniature; should not exceed 102 mm. (4") diameter.

Pompons; should not exceed 52 mm (2") diameter

Note; Judges use a set of ‘rings’ to determine these sizes.

To comply with the group sizes; the 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!

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 group list.

Dahlia culture;

Week 2-3; Check over dormant Dahlia tubers, remove any rotten parts, and dust with sulphur powder.

Week 5-6; 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.

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.

Week 12 onwards; take 50-60mm long cuttings.

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.

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.

Week 19; 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),

Week 22; 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.

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.

* Note; 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 these tubers and there is still a risk of frost, cover them with agro-fleece for protection.

Week 25/27; 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.

Note; Dahlias require copious amounts of water during their growing season.

Week 26/28; Top dress the beds with a fertiliser such as Fish, Blood & Bone.

Note; 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.

Daily empty out the pots and squash any earwigs that you find.

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. (See note above)

This will give better quality long stemmed flowers.

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

Week 35-36; 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 onwards; lift once the foliage has been blackened by the first frost, but if this does not happen, lift from 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.

Bedding Dahlias

Bedding dahlias; sometimes known as ‘Dwarf bedding dahlias’ will thrive in most types of well-drained soil, that has preferably 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.

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 in terms of location, feeding & watering as for ‘disbud’ dahlias.

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.

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.

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.


Sow seeds		Cover seed and water		Ready for propagator		Seeds germinated

Week 12 onwards; take 50-60mm long cuttings.

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.

Week 13-14; When seedlings are large enough to handle, prick out into 75mm (3") pots of potting compost.


Remove plug		Plug ready for potting on		Tray prepared to receive plug

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.

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.

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.

Daily empty out the pots and squash any earwigs that you find.

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 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.

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