Dahlia 101

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This page has instructions for both dahlia tubers and plants, so please read the appropriate section(s) below.


Upon receiving your dahlia tubers, store them according to instructions provided. The correct planting time will depend on your local conditions. Planting time is after receiving the last frost and temperatures have warmed. Typically, in the northern provinces this is around September and in the western provinces, around October. Plant them according to the instructions provided. If you need more information, be sure to read below.


1. Tubers

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1.1  Storage

Tuber storage (or overwintering) is one of the most important aspects that can be detrimental to the life of your dahlia tuber if not done correctly. During this dormant time, your tubers need a few specific conditions to ensure they remain happy – cold, the correct moisture and darkness. Of these, temperature and moisture are the most important. 

  • Temperature – keep them in an area that receives between 6 and 10 deg Celsius. Anything above 10 will signal them to break dormancy.

  • Moisture – not too dry and not too moist. Too dry will cause them to shrivel up and they might not recover. Too moist will result in fungal growth and they will rot. 

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What if…?

My tubers have already broken dormancy and started to grow shoots?

If they have just started to grow shoots from their eyes, don’t panic. Keep them in a bit cooler conditions until you are ready to plant them. If the shoots are already 10cm or longer, you can either plant them in a pot and keep the pot in a protected (warmer) spot that receives enough sunlight or you can break off the shoot (it will regrow) and move the tuber to cooler conditions until you are ready to plant them.


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My tubers are very soft and squishy to the touch?

If they still have some rigidity to them, they are just a bit dehydrated and will recover when you plant them. If they are very soft and have no rigidity anymore, they are most likely rotten and you should discard them.


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I notice mold / fungus have started to grow on them?

Remove the mold as much as you can by rubbing it off. Spray the area where the mold was lightly with a 10% peroxide solution or if you have some fungicide, you can spray with that. Discard the old packaging and put your tuber in new packaging. Wash all utensils that you used for this procedure.


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My tubers have shriveled up?

They will most probably still be viable. If you are able to, plant them in the ground or in a pot. Make sure to wet the soil slightly at planting time, so that the tuber can absorb the moisture, but do not make the soil too wet.


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1.2. Planting

Planting directly in soil

  • Make a hole for your tuber – about 15 to 20cm deep.
  • Add a handful of bonemeal at the bottom of the hole.
  • Place the tuber flat on top of the bonemeal
  • Add the soil back on top so that the top of the tuber is covered with around 10cm of soil. 
  • If the soil is very dry, water the soil around the tuber, but be careful to not overwater the soil.
  • Do not water again until you see a sprout breaking soil. Then you can water twice a week, depending on how hot the weather is. 

Planting in a pot (if your tuber has broken dormancy and have long shoots)

  • Use a big enough pot (5-10L) and add some stones at the bottom for drainage
  • Add a rich mixture of sand and fine compost and fill up to 10cm from the top.
  • Make a hole and insert your tuber (laying flat or with the stalk pointing upwards) and add the rest of the mixture on top. Ensure that you bury about half of the new shoot under the potting mix, letting the other half sit above it.
  • Make sure to place your potted dahlia in a warm spot that is protected from rain and receives enough sunlight.

Watering and feeding

  • During the hot summer months, your Dahlia plant will require a lot of water, either from rain or irrigation, depending on where you live.
  • At the start, feed with a high Nitrogen liquid fertiliser and after 2 months you can start feeding with a low Nitrogen fertiliser. You can use any fertiliser that is intended for fruit or flowers (they will have a higher Phosphorous and Potassium content than Nitrogen).

2. Plants

2.1 Planting Instructions

Planting directly in soil (if you have a spot that has well-drained soil and receives more than 6 hours of direct sunlight each day):

  • Make a hole in your soil – around 20-30cm deep.
  • Mix a spade of compost and a hand full of bonemeal with the existing soil at the bottom of the hole.
  • Place the plant on top of the soil mixture
  • Add the rest of the soil around the plant to fill up the hole.
  • If you plant more than one plant, space them 40cm apart.
  • Water the soil around the plant well so that the roots settle.
  • Thereafter for the next 2 weeks, water regularly to help the plant establish.
  • Then you can water twice a week, depending on how hot the weather is.


Planting in a pot (if your garden doesn’t have well-drained soil or a spot that receives 6-8 hours of direct sunlight):

  • Use a large enough pot (10L-20L) and add some stones at the bottom for drainage
  • Add a rich mixture of sand and fine compost and fill up to 30cm from the top.
  • Make a hole and insert your plant and add the rest of the mixture around the plant.
  • Water well to help the roots settle in.
  • Make sure to place your potted dahlia in a warm spot that is protected from rain and receives enough sunlight (6-8 hours per day).


2.2 Caring Instructions 

  • Provide horisontal plant support when growing in windy areas.
  • During the hot summer months, your Dahlia plant will require a lot of water, either from rain or irrigation, depending on where you live.
  • At the start, feed with a high Nitrogen liquid fertiliser and after 2 months you can start feeding with a low Nitrogen fertiliser. You can use any fertiliser that is intended for fruit or flowers (they will have a higher Phosphorous and Potassium content than Nitrogen).
  • Water often in summer and feed regularly with a low Nitrogen fertiliser.