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Growing dahlias

Published on September 20th 2020
A close up of a flower
Dahlias are an absolute delight in the mid-summer garden and, with so many diverse shapes and colours to choose from, you can grow new varieties in your garden each year. These gorgeous blooms also make for beautiful cut flowers and it only takes a few stems to make an impressive bouquet.
Dahlias are so easy to grow and they require little to no attention, providing pure delight well into autumn with not much effort. If you're growing dahlias in your garden this year or would like to try your hand at growing them for the first time, this article will get you well on your way.
A yellow flower

Planting Dahlias

Time it right
Dahlia tubers are best planted out in late spring when the soil has warmed to 15 degrees Celsius. Dahlias are sensitive to frost and will not grow when the soil is still too cold.
You can also start your dahlias in containers in a protected area and transplant them when the danger of frost has passed.
Location is key
Dahlias grow and flower best in a sunny, wind-protected position, ideally in a spot that receives some shade during the hottest hours of the day.
Soil secrets
Dahlias perform best in fertile soil with lots of organic matter and good drainage. Drainage is especially important as tubers do not like to sit in soggy soil. Before planting the tubers, loosen the soil to a depth of approximately 30 centimetres. Mix compost and all-purpose granular fertilizer to the planting area.
A close up of a rock
Dahlias can be bought as dormant crowns with connected tubers.
After soil preparation, space tuber 40 cms apart and dig a hole for planting. Place the tuber in the hole with the stem/sprout upright and positioned no more than 3-5 centimetres below the soil surface. Be careful not to overwater newly planted tubers.
Dahlias need a consistent supply of water to grow at their best. Drip irrigation makes this an easy task, however, if you are watering by hand, do it once or twice a week and ensure you target the roots and keep the foliage dry. Adding a layer of mulch around your dahlias will ensure that the roots stay cool and reduce the loss of moisture.
A close up of a flower

Dahlia care and maintenance

When your plants have grown to about 30 cms tall, pinch off the growing tip to encourage lateral branching that will result in more stems to produce flowers.
If your dahlias have reached their full size, they will need to be staked for extra support, especially if you're in an area that receives strong winds.
When your dahlias have started to bloom, feed them once to two times a month with a fertiliser low in nitrogen. Stop fertilizing early autumn if you consider collecting and storing the tubers after their flowering season.
A close up of a flower
Keep an eye out for slugs and snails, thrips, and whiteflies.
A slug on the ground

Slugs and Snails


A yellow flower in the snow





Fortunately, dahlias are a gift that keeps on giving so keep harvesting the flowers to encourage continuous blooming month after month. This also means there will be more than enough to gift a friend, neighbour or colleague with a delightful home-grown dahlia bouquet.
Prune spent flowers back to the main stem to keep your plant neat, help to control pests and diseases, and to stimulate new growth and longer stems that are better for cutting.
A close up of a flower
Tip | If your cut dahlias are looking a little dull and droopy, revive them by making a fresh horizontal cut at the base of the stem, place the cut ends in 40 - 50 ml of very hot water for about 5 minutes, and then place them in cold water for display. Et voilà!
Check out @Gundula's posts below to see the magic happen.


Trick to revive weather beaten dahlia blooms: I picked some dahlias at midday, two hours before I could get them in water. So I recut the stalks , dipped them for 5min in boiling water and then placed them in cold water. Within a couple of hours they were looking perky again. I knew this to be good advise for euphorbias, but I didn’t know it worked so well with dahlias. Any other cut flowers you’d recommend giving similar treatment?

Learn more about Dahlias and browse numerous varieties in the Knowledge tab.

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