dahlia society of australiaNSW and ACT dahlias

Growing Dahlias - Frequently asked questions

 

Below are questions to some of the most commonly asked questions about growing Dahlias. We hope it will be helpful to you.

Just click on the question and the answer will drop down.

 

For further enquiries please email us here.

 

Advice given on this FAQ page is of a general nature and provided by experienced Dahlia growers. It is not to be taken as expert or professional advice.

 

Where did Dahlias originate?

 

The Dahlia originates from Central and South America between Mexico and Colombia.

 

dahlias

 

Illustrations originate from Cavanille's
"Icones et Descriptiones Plantarum",
1791 & Oct 1795.
Real Madrid Botanical garden.


The dahlia is named after the Swedish botanist, Andreas Dahl, who lived from 1751 to 1789.
From these single types Dahlia Breeders have developed the Dahlia to what we appreciate today.

 

 

When do I plant Dahlias?

As a general rule of thumb two weeks either side of Melbourne Cup Day:- the first week of November.
Be aware of local conditions, it is advisable only to plant tubers when the soil temperature is on the rise and the risk of frost is over.
In sub-tropical climate areas such as Qld. dahlias can be planted as early as September in the frost free coastal areas and be flowering three months later. However this means flowering during our hot summers, resulting in poor blooms. The exhibitors plant in December for flowering in March to escape the heat in time for their Show Circuits.
If in doubt contact your nearest society or group and get the local information.

When is the ideal location to plant dahlias?

shadecloth over dahliasThe best location to plant Dahlias in the home garden situation is an area that has morning sun and afternoon shade. Dahlias do grow very well under shade cloth and it has been found by the experienced growers the White and Sandstone 50% cloths give excellent results. The ideal height for such a structure is approx. 2.4 m (8’).

 

 

Cllick on image to enlarge.

What soil preparation is needed - Soil type?

preparing soilDahlias grow in most soil types. It is ideal to incorporate a good amount of animal manure during winter. Composted Cow and Sheep manure is ideal. The use of Poultry and Pig manure must be used sparingly because it is very strong and can cause damage to the developing root system.

It is beneficial to grow a green crop that is dug in prior to planting. Wheat, Oats, and Legumes are suitable which will increase the levels of organic matter in the soil. Chemical fertilizers are a good substitute and as a guide any complete fertilizer will give good plants and blooms. Apply and incorporate animal manure and chemical fertilizer approx. two weeks prior to planting tubers. A complete fertilizer will give good results and even better results with a follow up of a side dressing when you see the first buds appear.

 

 

Top photo: Preparing the soil.

Below left: A green crop. Below right: Dahlia buds.

Click on images to enlarge.

green crop dahlia buds

What fertilizer do dahlias need?

dahlia fertilizerDahlias need a balance of Nitrogen Potassium and Phosphorous. The best fertilizers to apply are animal manures such as Cow and Sheep complemented with a complete fertilizer that already contains trace elements. One must be aware NOT to apply fertilizer that contains high levels of nitrogen.

 

Too Much Nitrogen = Too Much Growth = Not many Blooms

If the plants receive too much nitrogen during the growing season it will affect the keeping qualities of the tubers for the following season.

 

Chemical fertilizers with an N-P-K of 8-4-8 or similar will grow good Dahlias. Basically if you can grow Tomatoes you can grow good Dahlias. Weakly Weekly applications of Sea-Weed based formulas are ideal for promoting root development.

 

The serious growers apply small amounts of Sulphate of Potash and Sulphate of Iron which will give excellent strong growth, better stems, vibrant flower colour and significantly more blooms.

 

Click on image to enlarge

The tubers are shooting - do I need to plant them?

growingIt is quite common for tubers to start to shoot/sprout early in storage. You have three choices

 

1. Plant them early and risk the early frosts which can severely damage the plant.

2. Ideally cut the shoots off making sure to leave a node for further shoots to come. The tuber will re-shoot delaying your planting for approx. 3-4 weeks.

3. The Shoot can be saved and Potted in a medium of course sand which will grow into an individual plant that will perform as well as the plants grown from the tuber.

 

 

Can I grow dahlias from cuttings?

Dahlias grow very successfully from cuttings and the plant grows just as well as a plant grown from a tuber. The benefit of growing plants from cuttings are that you can multiply your stock very quickly. It is generally accepted by the “Experts” that you get a better and healthier plant. To grow cuttings one must create a suitable environment, one that is warm and has good humidity. A foam box covered with clear plastic/glass is ideal if you do not have a propagating house. A two litre drink bottle or similar can be used successfully.

 

Below left: A typical propogating house. Below right: A step by step guide for taking dahlia cuttings.

Click on images to enlarge.

dahlia cuttingsdahlia cuttings

Are big tubers better than smaller ones?

If you have a choice it is best to plant the smaller tuber because the smaller one will develop its own root system far quicker that the big tuber. The big tuber continues to depend on the stored food resources in its tuber and only develops it root system much later. This is a huge advantage because when we get those first hot days the plant, with its own independent root system, will be far more resilient than the plant growing from the big tuber. Quite often the stressed plant dies.

 

How do I plant tubers?

If using stakes, plant the stake first. Tubers are planted horizontally, that is lying down with the eye end of the tuber approx. 50 mm from the stake. The tuber is ideally place in a hole approx. 10cm (4“) deep with the eye slightly higher than the tail. It is advisable NOT to put fertilizer in the hole but make sure the fertilizer is incorporated in the soil prior to planting. Keeping in mind as the tuber grows and develops roots, it is in this zone where the fertilizer is of most benefit. If growing in a high rainfall area tubers are best planted on raised beds which reduces the chances of rotting and plant losses.

Weed Mat is used successfully in a number of Gardens.

 

Below left: Tuber parts. Below right: A raised tuber bed.
Click on images to enlarge.

 

plant tuber

tuber planting

 

Do I have to stake the plants?

Remember they have to be supported with either a stake or a trellis (Like Tomatoes).

 

If using stakes, plant the stake FIRST eliminating the chance of damaging the tuber. If you prefer a trellis make sure the first horizontal wire is approx. 10 cm (4”) from the ground providing that first vital tie. The next horizontal wires can be installed 30 cm (12”) apart as required. Growing plants with Tomato Hoops is also successful.

 

stakesdahlia stakes

trellis

 

 

Do dahlias need much water?

After enduring the water restrictions over the last 6-8 years experiences have shown that Dahlias do not need as much water as previously perceived. Dahlias do extremely well with a dripper system. Daily applications deliver the water directly to the plant, at the same time reducing evaporation. Some enthusiasts have found that applying water several times during the day for very short periods has produced brilliant plants and by applying water this way during the day has reduced the levels of sunburn and burnt/scorched buds. Low level sprays are also effective. Applications of mulch are of great benefit by assisting with the retention of water and reducing evaporation. The mulch also assists with weed control further reducing evaporation. If you are still applying water with a hose remember it is best to water late afternoon because this gives the plants all night to recover.

 

Below left: A dripper system setup for dahlias. Below right: Mulching assists with the retention of water and reduces evaporation.

Click on images to enlarge.

 

drippersmulch

 

Do the plants need pruning?

YES! When the plant has developed the first 4/5 sets of leaves nip out the growing point and this will encourage the plant to send up laterals from each of the leaf nodes, giving you more flowers and a more compact plant.

dahliadahlia plantdahlia

            Taking out Centre                         Increases Laterals             Resulting in more Blooms

 

Cutting flowers is a form of pruning. Cutting at least two sets of leaves when you want flowers for inside encourages more prolific new growth and will certainly guarantee the flowers right to the end of the season. If not cutting blooms for a purpose be sure to regularly prune the spent flowers (Dead-heading).

Can I plant dahlias in between other plants?

Yes. But be careful not to plant tubers or plants closer than one metre from the outside perimeter of shrubs and trees. They will do reasonably well in between roses but be sure to put out extra fertilizer so as to eliminate competition which will result in poorly grown roses and poorly grown dahlias. Remember that dahlias like their share of sunlight so if possible plant them on the eastern side of other plants, fences and buildings giving the dahlia afternoon shade and Morning Sun. It is advisable to apply a wetting agent prior to planting ensuring maximum water penetration.

 

What is the best time to pick the blooms?

The best time to pick blooms is early morning while they are very fresh. Take your container filled with water to the plant and when you cut the blooms put them into the water ASAP. If you cannot do this re-cut the stem by taking off about 10mm and make sure the cut is at an angle. This allows the free up-take of water. By cutting the stem square the stem may sit flat on the bottom of the container restricting the up-take of water which reduces the life of the bloom/blooms. The stems do not have to be Burnt/Scalded or crushed to prolong vase life of the blooms. A couple of drops of Bleach is ideal in the vase/container you are displaying your blooms. To get the best results maintain a dead-heading program which will ensure the Dahlias will bloom for a long time.

 

Can I grow dahlias in pots?

If you have limited space Dahlias can be grown in pots on patios, balconies and in small back yards. It is best to have a 300mm (12 inch) –260mm (14 inch) pot filled with quality potting mix. A double hand-full of animal manure can be incorporated into the medium prior to planting. The Border Type Dahlias are excellent for this type of culture because they do not grow too high, reducing the need to support them. To get the best results, maintain a dead-heading program which will ensure the Dahlias will bloom for a long time.

 

Do I have to dig them every year?

dahlia clumpIt is preferable to dig and divide your tubers annually because if you don’t, you run the risk of the clump of tubers rotting in the ground, especially if you are in a high rainfall area. The other problem is if they are not dug and they survive you will have a cluster of shoots appear in the spring, resulting in a smaller plant with poorer quality blooms. As a last resort they can be left in the soil for one year but very advisable to dig them at least every second year.

 

When can I start to dig the tubers up?

They can be dug when the tubers are mature.

 

How do I know that they are mature?
When the plant starts to go yellow they can then be cut down to a height of 20cm, this can be as early as late April and early May.

Depending on your area the late Autumn Frosts will accelerate this process. It is strongly advised to leave the tuber clumps in the ground until at least June. You can cut down the plants if they are considered unsightly. Place some aliuminum foil over the cut stalks eliminating the chance of water getting down into the crown of the clump.

IF tubers are dug too early this increases the risk of dehydration of the tubers. Some people leave the tubers in the ground until they are ready to plant and just dig them and divide all in the one operation. Growers in wet areas cannot do this because tubers will rot in the ground.

Remember when digging them up be sure to cut all the way around the clump so you are sure to cut all the feeder roots before lifting. Otherwise if roots are not cut and the clump is lifted you break the neck of the tuber leaving it useless.

 

Below left: Aluminium foil can be placed over the cut stalks to eliminate the chance of water getting down into the crown of the clump.

Below right: When digging up the clump be sure to cut all the way around the clump to cut all the feeder roots.

 

diggingdigging

 

Do the clumps of tubers have to be divided?

It is advisable to divide the clump so you can reduce the chances of rot setting in resulting in all the tubers being lost. If you are not confident just split the clump in half, this gives you the opportunity to remove any damaged growth reducing the chance of rotting. Snails and Slugs are less likely to take up residence.

 

How do I divide the clump?

Washing the clump enables you to see where you can cut.

 

When dividing the clump be sure to:

1. Retain part of the old stalk which contains the eyes.

2. Do not damage the neck of the tuber.

3. Preferably leave some of the tail.
4. Name the tuber with marking pen or indelible pencil.

 

Below left: Labeled Tuber. Below right: Step by step on how to dig and divide the tubers.

Click on images to enlarge.

tuberdigging

tuber clump

 

How do I store dahlia tubers?

Generally the best way to store the tubers is to dig them and divide in the same operation.

 

The options are:

1. Saves room in storage.

2. If one tuber goes rotten it is contained in that tuber only. If left in a clump the whole clump may rot. They can be stored in a ten kilo polystyrene fruit box lined with newspaper with about 50mm (two inches) of potting soil mixed with coarse sawdust. Place the tubers in the box with the eye end lined up along the edge of the box because when they shoot you lessen the chance of damage when removing the tubers for planting or swapping with a friend. Then cover tubers including the eye end with another 50mm of the same medium. This reduces the chance of dehydration. Tubers should not dry out and are best to be kept JUST damp.

3. After dividing the tubers they can be put in a shopping bag with a similar medium and hung on a wall. Ideal if space is a problem. Don’t forget to put the name on the outside of the bag. 4. Alternatively clumps can be placed under cover such as a citrus tree (or similar) or under the side of a shed. Make sure snail bait is spread around the clumps.

 

Below left: Tubers can be stored in polystyrene boxes.

Below right: Tubers in plastic bags hanging from a wall is ideal if space is a problem.

Click on images to enlarge.

 

storage of tuberstuber storage

What pests and diseases do dahlias get?

The following pests can affect Dahlias- Thrips, Aphids, Two Spotted Mite, White Fly, Cut Worms, Mealy Bug, Snails, Virus and Powdery Mildew. The main thing to keep in mind is if you have an insect use an Insecticide. For Mites, use a Miticide and Snail Bait for Snails and Slugs. Virus appears in a variety of forms and severely distorts leaves and stunts plants. There is no cure for this except removal of the plant because if you do not, the virus will be transferred to neighbouring plants magnifying the problem for the following season. If in doubt feel free to email the DSA for further information. dahliasinfo@dahliasaustralia.org.au

 

Below: Digging out a dahlia plant.

Click on the image to enlarge.

removing dahlias

 

Where do the seeds come from?

Seeds come from the mature flowers. If wanting to keep seeds one must remove the dead petals out of the flower head so as to eliminate the possibility of botrytis (rot). Once the flower head is fully mature the seeds are separated from the old head and stored in a dry container until they are ready to be sown in the coming spring. All plants grown from seed grow into a normal plant and will flower all in the same season. The interesting thing with growing plants from seeds is that none will be the same as the parent but will display some characteristics of the parent. Be prepared to cull the seedling plants and only keep the ones that appeal to you.

REMEMBER all dahlias started off as a SEED.

dahlia seeds

 

 

Why do they revert to one colour?

The only reason that there is a colour reversion is that enthusiasts do not name or label the tubers or clumps or just get them mixed up in storage. What really happens is that the strongest plants survive resulting in more tubers of the same colour.

 

 

What are the best cultivars to grow?

The best cultivars to grow are the ones that appeal to you. Some select their Dahlias because they have good stems and are great for vase work, especially for the Church. Some select their Dahlias because they are Big, Different, Vibrant, Unusually Dark Colour, Multi-Coloured or to exhibit. If you are looking to grow types for exhibition go to the Top Cultivar Showcase page. These cultivars are available from the various Clubs and Societies around Australia.

 

When selecting new cultivars (Types) to grow one must be aware of a few points

• Some Dahlias grow better in some areas and not in other areas.

• Some Dahlias bloom early in the season and others bloom late in the season.

Grow the ones that appeal to you