Dahlias have had a new surge in popularity in recent years. Photo / NZME
Fashion is an interesting thing, stemming from demand driven through human behaviour, where a significant portion of the population desire and follow after the same items.
Dahlias have been growing in the popularity stakes over the past few years as the classic full flower look that is synonymous with hydrangeas, peonies and old fashioned style roses. Dahlias combine well with the indoor-outdoor flow of interior design.
In the garden centre we have discovered that this year the stakes are higher; one particular variety, Café au Lait, sold for sub-$10 in garden centres throughout New Zealand and they are reportedly re-listed on TradeMe for $39-$49. This has been the trend with house plants over the past few years but now dahlias seem to be following suit.
What is exciting is the aesthetic ornamental value of dahlias is being recognised. They flower for months. Starting from Christmas to mid-January depending on the variety, the blooms will continue through summer and often well into late autumn. This late summer colour comes when many other plants have finished and don't offer much interest.
Dahlias are also relatively hardy plants that are simple to grow. In many cases they can be planted and left largely to their own devices, providing summer colour year after year.
They can be situated in full sun or part-shade, and they handle a reasonable amount of wind in themselves, though damage can occur if soft growth ends up being snapped off. If plants are in a windy situation, flower stems may need to be tied up and staked to avoid damage.
Dahlia plants are grown from tubers, which are thick bulb-like pieces of root. The tubers are available in stores now. They should be planted out in the garden under the soil. As the temperatures warm in spring, fresh green growth will appear out of the ground and form a bushy plant. As the cooler temperatures arrive, usually around May and June, the plants die down, entering their dormant phase. The tubers can be left in the ground and will sprout again the following spring.
Multiplying/propagating dahlias
There are two easy ways that dahlias can be propagated by the home gardener wanting to increase their patch. These are by division of the dormant tubers or by cuttings.
Division of the tubers can take place once the plants are well established, about three or more years old. This involves digging up the tuber clump when the plants are completely dormant and separating complete tubers off the clump to start as their own individual plant. Larger tubers will usually produce flowers in their first year; smaller ones may need to grow for a season before commencing flowering.
Propagating from cuttings is best undertaken during early spring. Some of the new young shoots can be selected as they emerge from the ground. These can be dipped in a softwood rooting hormone and set into a plant pot with cutting mix. A bag should be placed over the pot to create a warm, moist and humid atmosphere. The pot of cuttings is best placed somewhere warm out of direct sunlight and checked every couple of days so they do not dry out.
Feeding for more flowers
Dahlias benefit from feeding with fertilisers high in phosphate with other trace elements. Tui Bulb Food or Ican Blood n Bone are ideal for well-structured soils just needing a boost. If the soil structure is lacking then fertilise your dahlias with Tui Sheep Pellets. Feeding should happen little and often. The first feed should be as the new shoots are appearing in September/October (take care not to have the fertiliser actually touch the plant as this will burn). The second time to feed is as the plants are starting to flower around Christmas. The third feed should be applied in late summer/early autumn (February/March) when the plants are still flowering. Feeding at this time will help the plant in the building of stored reserves in its tubers which will influence next season's growth.
Regular feeding will strengthen the plant to do two things. First, produce more flowers and second, a strong healthy plant stands up far better to the presence of disease and is far less likely to succumb than an unfed plant in poor soil.
Pest and disease control
There are two main pests to be aware of when growing dahlias and one disease. Slugs and snails love the fresh new growth as it comes through the soil in September. To them it is like Christmas dinner laid out to delight. This is easily remedied with the weekly distribution of slug pellets in September as the shoots are first coming through the soil. Once the shoots are a bit taller these cheeky pests tend not to be such a problem.
The second pest - the caterpillar - usually appears later in the season. You will know these have arrived if there are holes in the leaves and signature tiny black droppings on the leaves. There are a number of easy to apply remedies if this becomes a problem at your house.
The main disease that can affect dahlias is mildew. If this disease is going to happen, it will usually appear during the late summer months/early autumn. Mildew is an airborne fungus that generally populates when humidity is high and conditions are warm and moist.
If you find your dahlias succumb to mildew near the end of the season, they will often come back fine the following year. There are steps that can be taken to minimise incidence of mildew. First, ensure the plants are well fed (strong plants are generally less likely to succumb). Second, ensure any irrigation that is applied is delivered using a weeping hose or drippers. Avoiding water on the leaves, and ensuring any watering that is necessary is delivered in the morning rather than the evening, can help significantly.
If these factors don't deliver sufficient results then spraying with organic certified Gro Safe Free-Flo Copper as a preventative spray from mid-January will give another level of protection against mildew.
Varieties
We have more than 30 varieties of dahlia tubers in-store now and most garden centres will be the same. Some favourites to seek out are:
Dahlia Ice Crystal - white cactus type spikey florets. Medium flower size, plant growing 80cm-1m high.
Dahlia Kelvin Floodlight – decorative rounded florets form a dinner plate size bloom up to 20cm wide of bright vibrant yellow. Plant grows 80cm-1.2m high.
Dahlia Alfred Grille - Another cactus type dahlia, fluorescent pink with a contrasting yellow centre gives a spectacular show. Plant grows 80cm-1m high.
Dahlia Apache - Eye-catching vibrant red cactus type bloom. Plant grows 80cm-1m high.
If you haven't tried dahlias, now is the chance - tubers are available in stores now. There will be plants of a limited number of varieties available during October through December.
• Gareth Carter is general manager of Springvale Garden Centre.
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