Dahlia Planting Advice

What to do with your Dahlia Tubers when they arrive…

Dahlias are tender tubers, they vary greatly in size and shape and often look like a bunch of salamis gathered together.

Dahlia Planting Advice Tubers

Dahlias are very similar to potatoes, if you freeze a potato, at first it appears undamaged, but will quickly turn to mush as it defrosts.

You must keep your Dahlias ‘frost free’ and as dry as possible until the weather warms up and you can plant them out.

If they arrive during a cold spell the best thing to do is keep them in the box in your home but in a cool dark spot and not next to a heater or radiator! 

I store mine in a solid garden building and the most precious are in an unheated bedroom, just to be safe.

Cupboards are brilliant because they shut out the central heating to a large extent.

If they are stored in plastic just check the bags have ventilation….if not either open them up or cut some slits in the bags yourself.

Swan Cottage Dahlia Tubers will arrive in breathable reusable storage bags so you only need open the box to let the air circulate.

Dahlia Planting Advice

Once a Dahlia has been brought into a warmer environment it must be kept in damp compost to prevent it drying out and shrivelling up. This is how you ‘start them off’…

Planting Method 

I start mine in generous pots in late March and early April.

Make sure the Tuber has room to put out roots and grow. Pots are like shoes for your plants… they need room to wiggle their toes!

It’s important not to start them too early, dahlias can put on more than 30cm of growth before the last of the frosts and quickly take over your greenhouse!

You can hold back your tubers by keeping them cool (and asleep). You can then plant them straight out into the garden after the last of the frosts, they will flower slightly later. We had frosts into late May last year here in Buckinghamshire, so be careful.

Potted dahlia’s can be carried easily indoors for the odd night.

Pinching out

However you have started your Dahlias you will need to pinch out the tips of the main shoot as they grow.

Either use a sharp knife or squeeze between your thumb and forefinger, remove the main shoot down to the top pair of leaves.

You also will need to remove all but 5 shoots from the sprouting tuber.

This can seem a bit heart-breaking at first but it’s essential! Be brave!

We are encouraging bushy plants and with only 5 stems you will get strong vigorous growth that will produce a lot of flowers!

Too many stems diverts the plants energy, doing too much, your flowers and stems will be thin and floppy.

We will cover this in more detail as the season progresses so don’t worry.


Dahlias thrive in, full sun and fertile soil, with good drainage. If your soil is heavy then a layer of grit under the tuber will help with drainage and stop the tuber getting waterlogged.

Sitting in water can lead to rot and the loss of your plant.

To plant them, dig a hole about 30cm square and 30cm deep, but use your
judgement, some dahlia’s are bigger than others and over-wintered plants can be much larger, you want them to sit comfortably in the bottom of the hole with space for the tubers to fan out, don’t squash them in.

Dahlias are also extremely hungry and thirsty plants. Incorporating lots of good well-rotted organic matter will improve the soil structure. Adding multipurpose fertiliser will get your dahlia’s off to a great start (read the box carefully, never add more fertiliser than recommended).

Place a layer of well-rotted compost or manure in the bottom of the hole (on top of your grit on heavy soil) to give your tuber a comfortable cushion and it is a good idea at this time to also add a stake (e.g., a bamboo cane) so you don’t accidentally harpoon your tuber later!

Note: it is vital that the organic matter is well rotted, fresh manure or too much plant feed can lead to damage, the leaves will turn brown and crisp around the edges, making them look ‘Scorched’.

Back fill the hole with soil and more compost (or manure) and water in well.

Watering also settles the soil back around the tuber properly and give it a jump start so do not skip this bit (even if it looks like rain).


Dahlia’s need plenty of room and depending on the variety you need to space them to accommodate their eventual size and the tuber at least doubling in size during the season, about 60cm is our recommendation! If growing permanently in pots, I would recommend at least a 15L pot,

Note; not all Dahlia’s will do well in pots see our website for my favourite varieties for the container gardener


Most important, protect from slugs! The juicy new growth is like caviar to these naughty
molluscs and they can mow your Dahlias down over night!! 

The best slug control is snipping them in half as soon as you see them!

We’ve tried beer traps – Boddingtons was brilliant!

Nematodes are great but for us they would be too expensive, so we use organic (ferric phosphate) slug pellets.

We start scattering sparingly at time of planting. Applying control before you think you need them will stop breeding in its tracks!

That should be enough to get you started!

More information will be available soon on Instagram stories

Zoe x