How to divide dahlias?

Dividing Dahlias

Jane Edmanson

JANE EDMANSON: In my mind, Dahlias are the Kewpie Dolls of the flower world – flirty, brazen and joyous. Rich in their variety of colour and shape, they make a great display during summer and autumn.

But this is their winter reality. The flowers have obviously finished. The stems are now dying right back down to ground level and energy is being put into those fleshy underground tubers and now is the time to lift, divide and propagate.

Now you might be surprised just how many tubers are under the ground. A fork is a terrific way to dig them up and you’ll see that some of them have really finished and some are actually really soft and squishy. Well they’re no good at all. They’ve run out of energy, they’ve rotted away. Throw that one away – and the rest of them are nice and hard and if you push into them, you can feel just how hard they are. They look sort of like a lumpy old bit of octopus and some people say that they’re edible, but I think I’d rather eat a potato any day.

The reason that you do lift Dahlia tubers is because if you’re in a frosty area or your soil is very cold and wet over winter, they can easily rot, so you lift them up and that means then that you can divide them and to divide them is really quite easy.

Ok, to separate that one as an individual piece, just use your secateurs and cut as close as you can, without destroying the neck because that’s the area that you’re going to find…down here’s where the buds or the eye is and that’s important – like a potato – you need an eye or two, and they’ll reshoot and that’ll be fine. You can either do it individually or you can put a clump in like that. You don’t have to divide all of them up.

Now to store them, all you need is a polystyrene box or a cardboard box and with a little layer of mulch, just damp not wet, just damp…or you could use sawdust…just lay them down like that and just keep them away from rats and mice too because they like to eat these little tubers and just cover them up and that protects them over winter. Leave it like that for the next 3 or 4 months until you see those eyes shooting and then you’ll find that your dahlias will be absolutely home and hosed – just like that.

Another great garden species the Tree Dahlia. It’s calledDahlia imperialisfor its impressive imperial height. In fact, I’ve brought some in from home and they’re at least 4 to 5 metres high. Lots of people think that the canes of the tree dahlia look just like bamboo, but it’s not. They really have some lovely flowers in autumn and going on into winter. This is a single white one. You can tell it’s just finishing. I’ve got a double white one, there’s beautiful pink and mauve tree dahlias as well and they’re dead easy to propagate from.

Cut the stems and what you’re looking for these little bits here – they’re the nodes or the eyes and that’s the bud that will come out and if you just chop them into pieces. Just use a secateur or whatever you’ve got. Cut them so that you’ve got 2 or 3 different nodes along the bit and each of those bits will grow.

You can either stick them into a pot or into the ground just like that and cover up a couple of the nodes with soil and then those will shoot up or you can do it this way – and this is really easy. Just put them into a pot or a polystyrene box and just cover them up just ever so slightly with some potting mix and you’ll find that each of those…where the node is there – that will shoot up and in spring, you can take those out of the polystyrene box and put them into the garden.

Whether it be the tree type dahlias or the herbaceous types, if you’ve planted these out in spring, you can be assured that your garden will be absolutely flourishing with delicious dahlia colour. Happy growing.

COSTA GEORGIADIS: Covering 18 hectares, this is the largest of the 6 islands on Sydney Harbour and it’s had a really interesting past. The island was used as a prison in settlement days and all the structures on the island were hand built from sandstone by the prisoners. Later on, the island was transformed into the largest ship building yard in the country where they made warships for both World War I and World War II. More on the island later, but now let’s head to Jerry who’s finding out just what it takes for a garden to become a part of Open Gardens Australia.

Tips On Starting Dahlia Seeds: Do Dahlia Seeds Turn Into Tubers

Dahlias are true summertime standouts in the landscape. The sheer array of size, color and form make these wonderful tubers a garden favorite both easy to grow and multiplying over time. Dahlias are most commonly started from tubers, but you can collect seed and increase your favorite flowers over time. You will need a little patience though, as dahlia flower seeds take several seasons to produce blooms, but the effort is fun and can yield some surprising results from these naturally hybridizing plants.

Dahlia Seeds vs. Bulbs

Dahlia tubers are common in nurseries and seed catalogs. They are the fastest and most reliable way to grow big, boisterous blooms. Growing the flowers using dahlia seed vs. bulbs may take a little more time but is a great way to extend your crop of the dazzlers. Knowing how to plant dahlia seeds isn’t hard, but there are a few tips for guaranteed success and riots of colorful blooms. Save your seed for inexpensive consistent dahlia season after season.

Dahlias most accurately grow from tubers which, like bulbs, are underground storage organs containing the DNA or blueprint of the plant. Vegetative methods of propagation result in true copies of the parent plant while seeded propagation is prey to the capriciousness of nature and may result in slightly different versions of the parent. For this reason, starting dahlia seeds is not a method favored by

collectors and champion breeders. You just never know what you are going to get.

Dahlia flower seeds are produced in prolific amounts on the plants but most gardeners simply protect the tubers and replant them the next year as a surefire way to keep a favored species. However, the adventurous gardener may want to save some of that seed and see what the next season brings. It might be a bloom that surpasses its parent in beauty and form.

How to Plant Dahlia Seeds

It can take a full season for you to see flowers on your seeded dahlias. Do dahlia seeds turn into tubers? In the first year, slender tubers will form but they will not be anything worth harvesting and will need another year or two to develop good growth nodes and produce bodacious plants.

The first step to starting dahlia seeds is harvesting ripe, ready pods. Pods contain numerous seeds. Wait until the flower has dropped all its ray petals and the pod is a light tan-green color. The seeds inside should be ripe and gray to dark brown.

Cut the pod off and let it dry to facilitate removal of the seeds. Separate the seed from the rest of the pod and allow let dry before storing. In early spring, germinate the seeds in soilless seed starting mixture in flats.

Sow your seeds an inch apart on the surface of the mixture and cover lightly with a dusting of the medium. Moisten the medium and keep moderately damp, moving the flats to a warm location of at least 70 degrees F. (21 C.). Germination will occur in 7 to 12 days after sowing.

Once the seedlings are large enough that their leaves are touching, individually pot them up in 3-inch containers. Harden the seedlings off before planting them out into prepared garden beds. Wait to plant them outdoors until all danger of frost has passed.

Alternatively, you can plant them outdoors a week before the date of the last frost. In northern climates this may not give the plants enough time to develop and bloom. It works great in long season areas, however. If cold temperatures threaten at the end of summer, repot the plants and move them into a greenhouse or indoors.

They won’t have much tuber development and the best way to save them for next season is to let them go dormant indoors where icy temperatures can’t damage the tiny root and tuber system. Harden them off the next season and plant outdoors. You will get big beautiful plants with plenty of appealing flowers that will set pods and start the whole growing dahlia seeds process over anew.

Dahlias

Circular 576 View PDF picture_as_pdf

Paul A. Thomas, Extension Horticulturist

  • Getting Started
  • Location
  • Soil
  • Planting Procedure
  • Rooting Cuttings
  • Staking
  • Fertilization
  • Watering
  • Disbudding and Pinching
  • Digging Tubers
  • Dividing Tubers
  • Cutting Flowers

Dahlias are among the most spectacular flowers you can grow in your garden. Hundreds of varieties are available, with flower sizes ranging from 1 to 14 inches in diameter. Almost any color except true blue can be produced in Georgia.

In exchange for their beauty, dahlias require dedicated care. Most of them need special soil preparation, staking, watering during dry periods, disbudding and a strict insect control program.

Dahlias grow to perfection in the cool, moist summers of the north Georgia mountains. They are also well adapted to the state?s Piedmont area. Dahlias are more difficult to grow in the Coastal Plain area because of its high summer temperatures, but you can expect good flowers here, especially during cool, cloudy periods.

Getting Started

Named dahlia varieties are usually bought as tubers, which are simply enlarged roots. You have a better chance of good results if you buy named varieties instead of those labeled only by color.

Tubers are available in late winter and spring. Most dahlia authorities, however, are in no hurry to plant tubers. They know that the most beautiful flowers come from late plantings that flower at their peak in September and October. Tubers are often planted in April in south Georgia and May in the northern half of the state. June plantings often give the most perfect fall flowers. If tubers are planted early, cuttings can be taken from them in May to produce a late-flowering crop.

Location

Dahlias thrive in the sun. Place them so they get at least a half day of direct sunlight. They seldom do well in heavy shade or in competition with trees. The location should also have well-drained soil ? dahlias will not grow well in areas where water stands for any length of time.

Soil

The top growth of dahlias is in direct proportion to the extent of the root system. A good root system can be obtained only by proper soil preparation. This means digging a large hole ? 24 inches wide and 18 inches deep is a good goal.

The ideal soil is loose and crumbly, holds moisture well and provides good aeration. Most soils fall short in all these characteristics, but a desirable soil for dahlias can be created easily by incorporating organic matter in the soil removed from digging the hole. The old standby organic matter is well-rotted cow manure. If this is not available, materials such as peat moss, pine bark or decomposed leaf mold are acceptable substitutes. Mix 1/3 organic matter with 2/3 soil. If your soil is on the acid side, add a cup of agricultural lime to the mixture.

Planting Procedure

If you are short on time, plant the tubers in pots or gallon cans and transfer them to the ground when you have time to prepare the soil properly. The tubers are usually placed 4 to 6 inches deep. Be generous in spacing. Most varieties need to be at least 3 to 4 feet apart.

Rooting Cuttings

Allow only one shoot to develop from the tuber. The other “slips” can be removed and rooted easily if you want additional plants. To do this, wait until the growth is approximately 10 to 12 inches high. Pull the soil back from around the underground stems and cut off the extra shoots near where they emerge from the tuber. The cuttings should develop sufficient roots for transplanting in two to three weeks. After transplanting, shade the young plants for a week with newspaper or similar material. Water carefully during this period.

Staking

You?ll be in for a big disappointment if you don?t stake your dahlias. Since most of the better varieties grow tall, they cannot support themselves when they reach maturity. A heavy wind or rain will destroy them.

Stakes need to be at least 6 feet long to be useful. Drive them about 1 foot into the ground. The easiest time to do this is at planting time. Some growers prefer two stakes about 18 inches apart to support each plant.

When the plants are about 1 foot tall, tie them to the stakes with soft string or cloth strips. Repeat about once a month as the plant grows taller. The limbs that bear the flowers especially need support.

Fertilization

If cow manure is used as a soil amendment, it is not necessary to add fertilizer at planting time. If peat moss, pine bark, leaf mold or similar materials are used, about ¼ cup of balanced fertilizer per plant should be adequate when preparing the soil. Each month thereafter, fertilize the dahlias with 1/8 to 1/4 cup per plant of balanced fertilizer. When the plants are large (5 to 6 feet), increase the rate to 1/2 cup per plant. An analysis with a 1-1-1 ratio such as 8-8-8 is good. Most other fertilizer analyses that give satisfactory results in vegetable and flower gardens can be used successfully for dahlias.

Watering

Dahlia plants are composed mostly of water. Don?t expect good flowers unless you plan to water during dry periods. Give the plants a good soaking once a week. Light surface applications will not do the job.

To conserve the water you apply, mulch the plants. A wide variety of materials can be used successfully, including pine straw, grass clippings, pine bark and black mulching plastic. If a mulch is not used, watering twice a week during dry periods will be desirable.

Disbudding and Pinching

When the young plant has produced three or four pairs of leaves, pinch out the top. This is done to cause the plant to produce side limbs.

Disbudding is another vital cultural practice. It involves nothing more than removing some of the flower and growth buds on each flower stem. Beginners are sometimes reluctant to do this. Unless dahlias are disbudded, however, they will not produce large, perfectly formed flowers on long stems.

When the flower buds of the tip cluster are about the size of peas, remove all but one. At the same time, pinch out the small, tender growth buds in the leaf axils of the top set of leaves on the stem. You might also need to do the same for the buds coming from the base of the next set of leaves if the variety produces short stems.

Remember that dahlias produce more flower buds than the plant can supply with food. Disbudding is necessary to channel sufficient food to a select number of flowers.

Digging Tubers

Overwintering tubers of good dahlia varieties in the ground is an unwise practice. A severe winter may kill them all. Most dahlia growers dig the tubers after the first frost.

Careless digging can destroy the tubers. Note in Figure 1 that the “eyes” or growth buds occur only in the area connecting with the underground stem. If the tubers are pulled off or if they break off, the buds are almost always lost and the tubers are worthless.

Figure 1. The “eyes” or growth buds occur only in the area connecting with the underground stem. If the tubers are pulled off or if they break off, the buds are almost always lost and the tubers are worthless.

Allow the dug tubers to dry for a day before you store them. A 35 degrees F to 50 degrees F storage temperature is desirable. If the storage area is moist, store the clumps without packing. Many growers store them in large boxes and cover the clumps with dry vermiculite or similar dry materials.

Dividing Tubers

A single tuber planted in the spring will multiply into a number of tubers by late summer. If the clump is not divided, many stems will emerge the following spring. This is not desirable. The most vigorous plants with the best flowers come from individual plants and not from clumps. For this reason, divide dahlia tubers each year. This is done by carefully cutting the tubers apart with a sharp knife as illustrated in Figure 2. Since each tuber must have an eye or growth bud, many dahlia growers delay dividing until early spring when the buds have swollen and can easily be seen.

Figure 2. A cluster of tubers can be separated by cutting with a sharp knife. Be sure each tuber contains a portion of the underground stem with an eye.

Cutting Flowers

To prevent wilting, cut only in the early morning or late afternoon. Place flowers in warm water immediately after cutting. The temperature should be warm but not uncomfortably hot to the touch. Cut flowers only after they open to mature size ? they will not open after cutting. Also, they are less likely to wilt after reaching maturity

Status and Revision History
In Review for Major Revisions on Feb 24, 2009
Published with Minor Revisions on Jan 31, 2012
Published with Full Review on Jan 23, 2015

Dwight’s Dahlias

SERIES 29 | Episode 14

Jane Edmondson visits her old friend Dwight King, President of the Dahlia Society of Victoria, to find out more about growing Dahlias. A retired Airforce pilot who also had a career in IT, Dwight was influenced to grow Dahlias from his family’s strong gardening heritage back in the United States of America. Here in Australia, Dwight found walking through his dahlias was a great way to destress at the end of the day.

Dahlias are named after Andreas Dahl, a Swedish botanist and student of Linnaeus. A member of the daisy family, the seed was introduced to Europe in the 1700s and growers have been producing hybrids ever since.

Dahlias flower from Christmas to the end of May in Melbourne, so you have something for a vase 6 months of the year. These floral extraverts come in many shapes and sizes. There are 42 species of dahlia, but it is the multitude of hybrids that are mostly available now. These are grouped into 16 types: decorative singles or cactus types with pointy petals, ones with peony-shaped flowers, spherical ball and pompons to anemones, fimbriated ones with split ends to the ‘petals’ and large flat collarettes.

In shows they are measured with rings and need to be as close to perfect as possible. To achieve the perfect bloom, smaller side shoots are disbudded so that all the energy can go into producing one central flower. Alice, Dwight’s wife does flower arrangements and needs longer stems, which you get if you cut out extra buds.

Dahlia growing tips

  • Dahlias prefer a cooler climate without heavy frosts – tubers will rot in frozen soil over winter, so you get around this by lifting them every winter and storing them somewhere dry.
  • Dahlias prefer morning sun and afternoon shade; Dwight uses 50% white shade cloth to protect them, which also enhances the flower colour (full sun bleaches the colour out).
  • Dahlias enjoy regular watering and spray water under leaves as well to remove any insects.
  • uses a blend of seaweed solution, soil conditioner and fish-based fertiliser, sprayed onto the top and underside of their foliage. Dahlias are gross feeders, but this blend also forms a sticky solution that helps stop insects.
  • Snails and slugs are a problem when they’re young.
  • You need to divide dahlia clumps to get more flowers

For beginners Dwight says imagine fitting a standard folding trestle table in your garden: “You can put twelve dahlias in that space,” he says.

Year-round schedule for showing:

  • In spring take tubers out of store (or lift) and divide them up; there might be 10-30 new
  • tubers attached to original one
  • Plant a single tuber in the spring, making sure each has an eye
  • Lay them on potting mix to see if they start to shoot to check they’re still ok
  • Once shooted, plant one on either side of a stake (for support)
  • After 6 pairs of leaves, nip off tip bud to avoid getting a single stem with a single flower
  • If growing a large flower allow 3-4 laterals (side shoots) – for smaller flowers allow 6-9 laterals.

Method for Pruning:

  1. As dahlias finish flowering remove the top third of growth to send more energy back to tuber
  2. As it yellows and starts to die down, remove another 1/3 of the growth
  3. When the bush completely dies off, cut back again leaving a small stub4) Dig up the tubers to store over winter in all but the most well drained soils.

Other useful links

Dahlia Association of Australia

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