Start potting up dahlia tubers at the beginning of Spring, as this is when they’ll naturally start producing shoots.

At the end of February, after I’d been bursting with anticipation for 6 whole weeks, the dahlia tubers arrived in the post. At the end of March, I started to pot them up. You can start dahlia tubers in pots in March or early April. This is called potting them up.

By potting up dahlia tubers, we give them a chance to start growing earlier, in a frost-free place, so that by the time the garden is ready to receive them, in late May, they have grown into good-sized plants, with their roots already well-established.

I also had some tubers which over-wintered in a mixture of dry compost and perlite, in the garage, which I had grown the previous year from seed.  These are the ‘Bishop’s Children’ variety, which are single-petalled, and some have darker, more bronzy leaves and stems. The flowers are a mixture of reds, oranges, yellows and pinks.

Why Pot Up Dahlias First?

Dahlia Black Jack shoots

Tender shoots of Dahlia ‘Black Jack’

So why do we pot up the dahlia tubers instead of putting them straight into the ground or a large pot outside?

This is because we want to get the dahlias growing as early as possible, for the longest flowering time.

In March, the soil in our Scottish garden is still wet and cold, and until the end of May, we might get frosts, which destroy dahlias.

Dahlias are native to warm climates and are tender plants that will rot in cold, wet soil.

By potting up dahlia tubers we give them a chance to start growing earlier, in a frost-free place, so that by the time the garden is ready to receive them, in late May, they have grown into good-sized plants, with their roots already well established. 

Being bigger when they’re planted out also helps dahlias to have a fighting chance again slugs and snails.

Check dahlia tubers

Overwintered dahlia tuber Dahlia Bishop's Children

Over-wintered tuber of Dahlia ‘Bishop’s Children’

Take the dahlia tubers out of their packaging, or dry compost mix, and check each one for signs of damage.  Healthy tubers should be firm, not soggy.

The tubers look a bit brown and insignificant now but contain so much colourful flower power.

What you’ll need

What you will need to pot up dahlia tubers - compost and a 2L plant pot

Compost and a 2L plant pot

To start potting up your dahlia tubers, you will need:

  • 2L pots or trays just deep enough for the tubers
  • Compost
  • I usually add some perlite to the compost too, to help water drain away through the compost easily

Dahlia tubers don’t need much nutrient content in the compost at this stage.

How to pot up dahlia tubers

Potting up dahlia tubers - Bishop's Children Dahlia tuber

Put one tuber into each 2L pot

  1. Add some compost into the pots or trays.
  2. Put one tuber into each 2L pot, or a few in a tray.
  3. Cover the tubers with compost, almost to the top of the old stalk.
  4. Water a little if the compost is dry, but don’t saturate the compost.
  5. Place in a light, warm, or at least frost-free place, such as a greenhouse, mini greenhouse or windowsill.

 

Potting up dahlia tubers - almost to the top of the old stalk

Cover the tubers with compost, almost to the top of the old stalk

J Parkers recommend soaking the tubers in water for up to 24 hours before potting them up.

The tubers that I over-wintered in a pot of compost and perlite feel firm and ready to burst into life, in fact, one tuber already had shoots when I lifted it out of the compost.

The mail-order tubers seem much drier, so I think it might be a good idea to try soaking these before planting.

Place in a light, frost-free area

Since I don’t yet have a greenhouse or polytunnel, I put the dahlias that I’ve potted up into a mini greenhouse.

I’ll leave them like this to grow shoots, for around 6 weeks, keeping them a little moist but not too wet. Soon the tubers will grow lovely big shoots, which can be pinched out to encourage bushier growth. The growing tips that you pinch out can also be used as cuttings to start new plants, which are clones of the original plant.

Slug protection

Dahlia shoots planted with a mulch of wool pellets

Dahlia shoots planted with a mulch of wool pellets

I am trying wool pellets this year to see if they help keep slugs and snails away.

Dahlia Varieties

4 dahlia varieties arrived from Sarah Raven.

  1. Dahlia ‘Zundert Mystery Fox’
  2. Dahlia ‘Black Jack’
  3. Dahlia ‘Jowey Winnie’
  4. Dahlia ‘Totally Tangerine’

Conclusion

Potting up dahlia tubers in easy.  At this stage, you only need to put a tuber into a large enough pot to hold the tuber, cover almost to the top of the old stalk with compost and keep it out of the cold and wet.  Healthy dahlia tubers should then sprout lots of shoots for this year’s growth, and enough for some cuttings too.

What are your favourite dahlia varieties?  I’d love it if you could let me know in the comments.

Happy dahlia potting!