|
Dahlia Culture
Classification
Single, Semidouble
Double-Flowered
Culture and care
|
Dahlia
Culture
CULTIVATION AND CARE
Dahlias are rewarding plants: the better
care they receive, the more you will be compensated with vigorous
growth and lavish flowering. The conditions we list here for
good care are general in nature. Differences in soil types,
temperature, light and nutrients can all affect development.
By experimentation, everyone can discover what the ideal care
is for their own dahlias
|
| Soil |
Dahlias will grow in any type of soil.
It is important, however, that the soil provide nutrients
and be permeable but not exceedingly dry. The ideal pH (acidity
level) is 6 to 7. The use of lime can increase the pH.
|
| Location
|
Always give dahlias
a spot where they will receive plenty of light. They can tolerate
sun all day long. In sheltered gardens that become very hot,
a few hours of shade every day will not cause any harm. Too
much shade, however, will result in tall, limp plants with fewer
flowers. |
| Watering
|
Always give dahlias
sufficient water. The soil should be kept constantly moist.
Once fully developed, the taller varieties in particular can
transpire a lot of water from their many leaves on hot days.
Insufficient water will lead to slow growth, few flowers and
yellowing leaves. |
| Nutrients
|
Dahlias demand good fertilising. Before planting them, provide
the soil with the right nutrients. You might even want to
have a soil analysis conducted by a soil sampling laboratory.
An organic granular fertiliser is very suitable for adding
before planting and is environmentally friendly as well. During
the vegetative period, provide some supplementary balanced
fertiliser on a regular basis (e.g. NPK 12-10-18 in granular
form). Scatter the granules generously around the plants.
You can also use a fertiliser soluble in the water you apply
for irrigation. Do not make the solution too strong. Granules
can be applied once every four weeks; fertiliser dissolved
in irrigation water can be applied once every one or two weeks.
Make sure that the plants stay nice and green and continue
growing and developing new buds and flowers. It may take a
bit of experimentation to discover the exact amount of nutrients
your dahlias need.
|
| Temperature
|
Dahlias thrive
at temperatures between 15 and 25ºC. Having evolved in the warm
climates of Mexico, they will not survive a cold winter. They
tolerate no frost whatsoever. For this reason, do not plant
them out until the danger of ground frost is over (around mid-May).
This applies to both cuttings and pre-forced plants. If you
are planting tubers, you can put them out around 20 April because
it will take them 2 to 3 weeks to emerge above the soil surface.
|
| Planting material
|
Dahlias can be purchased as various kinds
of planting material. Tubers are on sale in early spring at
garden centres, seed businesses, mail order companies or at
specialised nurseries. Two different kinds of dahlia tubers
are sold:
Dahlias propagated from cuttings
These dahlias have been propagated vegetatively
by taking cuttings from dahlia tubers. Growers call these
'propagating tubers'. These tubers have been carefully selected
for their soundness and trueness to variety to be sure that
the best material is being used for propagation. All plants
obtained in this way will be identical in regard to their
variety: the same flower, plant and colour. The packaging
will usually display a photograph.
Dahlias propagated from seed
These dahlias have been grown from seed.
Although the tubers look almost exactly like those propagated
from cuttings, there are still certain important differences.
These dahlias are always purchased mixed; after all, nobody
can predict the exact characteristics of a dahlia propagated
from seed. The variations in colour, floral type, height,
etc. can be fairly great. Two kinds of dahlias propagated
from seed are available: Mignon mixed single-flowered dahlias
and Unwin mixed, usually partially double dahlias. The packaging
usually shows a picture of a mixed group of dahlias. The packaging
is required to state that these are dahlias produced from
seed.
Tall varieties should be planted about
50 to 60 cm apart, the lower ones about 25 to 30 cm apart.
The tubers are placed just a few centimetres beneath the soil
surface. After planting (especially in the case of cuttings
or pre-forced plants), make sure to provide enough water for
a few days.
|
| Planting
|
You can start planting dahlia tubers 2
to 3 weeks before the risk of ground frost is over. They will
not emerge above the soil surface until there is no longer
any risk of frost.
If you have a greenhouse or a cold frame,
you can pre-force these tubers in pots. If you do this, you
will have larger plants to put outside and will be able to
enjoy flowers sooner. You can also plant dahlia cuttings.
These are usually available only by ordering from specialised
dahlia nurseries or getting them from a local dahlia society.
(For information about societies and/or specialised commercial
nurseries, you can contact the Netherlands Dahlia Society.)
For several years now, certain garden centres
have also been selling flowering dahlias in pots during the
months of May and June. You can take these out of the pots
and plant them in the garden or transplant them into larger
pots, flower boxes or containers. If transplanting to pots,
make sure to use ones of sufficient size that hold at least
10 litres of soil to reduce the risk of their drying out on
pretty, sunny days. This way, your dahlias can receive a spot
on the deck or the patio. And by moving them around and combining
them with other tub plants, the look of the garden keeps changing.
|
| Further care |
Taller dahlia
plants should be supported. These plants and their flowers can
become so heavy that they can fall over and break, especially
during hard winds. Sturdy canes to which the dahlias can be
tied are a good solution. Special plant supports (plastic rings)
available from garden centres are also ideal as supports and
visually more attractive. If you want compact, heavily branched
plants, you can pinch back the shoots so that only 2 to 3 pairs
of leaves remain. Then, the axillary buds will start to develop
so that more branching occurs. The result is a beautifully branched,
bushy plant with lots of flowers. The same thing can be achieved
later when flowers are removed. Cutting them away stimulates
the growth of new shoots. This is the same reason why faded
flowers should be removed. When removing faded flowers, clip
the stem back to the next axillary shoot. This deadheading is
especially important for single-flowered dahlias. If this is
not done, they will quickly go to seed, thus sapping the plant's
energy reserves and nutrition to develop their seedpods. Meanwhile,
the plant will not be producing any new shoots and flowers.
|
| Showflowers
|
Instead of many
flowers, one can decide to have the plant produce fewer but
much larger flowers. The results of such a procedure can be
seen at exhibition gardens and shows. With this method, you
allow no more than 5 shoots to develop per plant. On each stem,
you allow only the terminal bud to develop. The lateral shoots
are removed from the leaf axils. If done in time, they can simply
be pinched out by hand. Meanwhile all the nutrients will go
into the main flower to make it larger and more beautiful. There
are many dahlia societies in many countries of the world that
hold these flower competitions and organise shows. Anyone interested
can obtain information from the Netherlands Dahlia Society (NDV).
It is very likely, too, that there will be a dahlia society
close to where you live. From such societies you can learn much
about the care of dahlias as well as about the many different
varieties. |
| Cutting dahlias
|
Dahlias are favourites
for cutting because of their many bright colours and their long,
straight stems. It used to be that their limited keeping quality
was an inhibiting factor in the marketing of dahlias as cut
flowers. Breeding efforts have been devoted to solving this
disadvantage, however, so that in recent years, several good
cutting varieties have become available. There are even certain
special cutting varieties that can be harvested while still
immature and which have a vase life of more than a week. Over
the last few years, these varieties have been increasingly included
in the flower auctions' and flower exporters' standard assortment
of summer flowers. The supply of the kinds of dahlias suitable
for flower production in greenhouses is now starting early in
the season. Those wanting to cut dahlias from their own garden
can simply put some of these plants in their garden. They are
also for sale at the market and from the growers themselves.
Dahlias should not be cut in the middle of the day. The best
time is the morning, but the evening will also do. Put them
immediately in plenty of water. Adding nutrients for cut flowers
will help the flowers develop better and will lengthen the vase
life since these agents also contain a substance that keeps
the water and vase clean. |
| Uninvited guests
|
As with all plants, dahlias too are visited
by pests such as aphids, caterpillars, slugs, thrips and earwigs.
Inspect the plants regularly and apply the appropriate control
agent when necessary; several effective environmentally responsible
agents are available.
|
| Propagation
|
There are three ways to propagate dahlias:
1.
By seed
This is fun to try sometime, but one should
keep in mind that the offspring will be very unlike their
parents when grown from seed. Goal-oriented crossing and thorough
selection is how growers produce new varieties. Even seed
that is purchased cannot guarantee a certain shape and colour.
2.
By dividing and splitting
Once you can see the first eyes developing
on the tubers from the previous year, you can divide the tubers
with a knife. Make sure the pieces you are going to plant
have at least one eye.
3.
By taking cuttings
Dahlias can be propagated very effectively
from cuttings. This method is used by growers for propagation.
The tubers are first planted in a heated
(approx. 20ºC) greenhouse in early spring. The cuttings are
taken when they are about 10 cm long. Remove the first shoots
right on top of the tuber and dispose of them. These are often
very coarse and hollow. New shoots will be quick to appear,
and these can be taken as cuttings. Plant them in a light
soil mixture that is not too rich in nutrients. Keep the soil
moist. A high humidity is important, too. After 2 to 3 weeks
at a temperature of approx. 15ºC, they will have developed
rootlets. They can then be transplanted to pots. Hardening
them off in time is important. This can be done in a cold
frame or in a sheltered spot outside. Watch out for ground
frost. They can then be planted outside around mid-May to
begin another new dahlia season filled with growing and flowering.
|
| Winterstore
|
Dahlias
will not withstand a cold winter. If you wish to store the tubers,
you will have to lift them before winter sets in. After the
first ground frost, the plants are pruned back to approx. 20
cm. Allow the stems to dry, and remove the tubers from the soil
before freezing weathers. Let the tubers dry and store them,
covered with dry peat litter, in a cool, dark and draught-free
place. Remember to attach a label with their variety or colour.
Tubers that you want to store should not be too wet but neither
should they be allowed to dry out (as can be seen by wrinkling).
Dahlias are available from garden centres, the supermarket,
plant and flower shops, at the market, and through trading and
mail order companies. For the very latest or very special varieties,
you might try visiting specialised dahlia nurseries. For obtaining
more information, contact a dahlia society in your area or the
Netherlands
Dahlia Society to which many of the local societies in the
Netherlands are affiliated.You will receive regularly scheduled
information about the cultivation of dahlias, the new varieties,
exhibitions in the Netherlands and abroad, and all kinds of
bits of news about dahlias when you become a member of the NDV.
|
|
