Basic Culture Tips for Growing Dahlias

Over the past few years dahlias have become increasingly popular, and rightfully so for few other plants offer the gardener such a variation in colour and form.  In 2013 we had a visit from a member of the Hobart Horticultural Society Dahlia Group who spoke to us on cultivating and showing dahlias and donated a number of tubers which were made available to members.

The following is a summary of that presentation which might refresh member’s memories.

Dahlias are one of the easiest flowers to grow,  No other autumn flower can produce the range of colours and types as does a dahlia.  Following the basic care procedures will give you an abundance of dahlia blooms.  Your garden will come alive with a coloured mass that will be the envy of your friends and neighbours.  The most popular method of growing dahlias is from field tubers, thus the following tips refer to this method.

LOCATION AND SOIL

A well-drained garden bed in full sun or semi sun is ideal.  Dahlias grow in all types of soil, preferably enriched with well-rotted stable manure, or just any old animal manure.  Prepare the soil at least two weeks before planting.

PLANTING

Dahlias may be planted from October to December. The most favoured time is early November – Melbourne Cup Day. Tubers should be planted 7.5cms (3”) under the soli ensuring the growing eye is facing upwards. Do not plant your tubers in very wet soil as tubers may rot before the shoots have a chance to emerge.  Do not water tubers when planting unless your soil is very dry. Note: The dahlia should not be watered until the growing shoots are 15cms (6”) above the ground.

Place your dahlias 75cm to 90cms (2’6”” to 3’) apart.  Locating stakes before hand prevents possible damage to the tuber. Plant the tubers 5cms (2”) from the stake. Snails and Slugs like the young shoots as they come through.

CULTIVATION

The growing stem should be stopped.  This means that the growing tip should be removed when the stem has produced 5 or 6 sets of double leaves.  Lateral growth will develop and grow from each leaf axis

As the plant developsand grows, it is important to keep the bush tied firmly to the stake. panti hose make good ties as they have a little give, make a figure 8 when tying.

Watering should be increased as the plant matures. At peak of flowering, a good watering every third day.

FERTILISING

Dahlias are gross feeders, however granular fertilizer should not be applied until the plants are well established.  A small handful of complete granular fertilizer(5.2.1) applied to moist soil and spread around the plant at the 8week and 12 week stage will be adequate.

MULCHING

Heathly, well grown dahlia plants will grow 135cms to 180cms (4’6” to 6’) tall and will produce leaf foliage.  To assist the plant during the hot summer months, a heavy mulch of straw should be applied in December when the dahlias are approximately 30 -45cms(12” to 18”) high

FOR LARGER BLOOMS (FOR SHOWING)

To improve bloom size and increase stem length and firmness, it is recommended to remove the side buds on each flower stem.  Additional laterals from the lower leaf axis should be removed for the larger size blooms (You will lose flower numbers).  For continual flowering over three or four months, the spent flowers should be removed.  The more you pick the blooms, the more flowers are produced.  Stop watering (approx. mid April) when the rain comes.

DIGGING AND STORAGE

As May approaches, dahlia plants should be cut down in stages.  The clumps of tubers should be dug and stored in June/July.  Leaving the soil attached will protect the tubers from drying out.  Store in a dry place protected from the sunlight.  An alternative method is to wash the tuber clump immediately after digging. Divide the clumps into section and allow to dry for three days and store in damp (not wet) hardwood sawdust over the winter months.  The saw dust can’t be green pine.  It is recommended that the tubers be inspected at regular intervals for rot or excessive drying out.  New shoots should appear in Spring and the cycle begins again.  If your soil is free draining and doesn’t hold much water, clumps may be left and lifted every second year.  Don’t dig too close to the stems as the tubers of some varieties can spread quite some distance.