Dahlias are popular flowers found in many UK gardens.
They can be grown from pot-grown plants, from seed, or from tubers.
In this guide, we will cover how to plant out dahlia tubers for the best results.
Dahlia tubers are best planted indoors into containers from February to March, though they can also be planted a little later directly into the garden.
To plant dahlia tubers you will need to:
- Select and source your dahlia tubers.
- Decide where to grow your dahlias, remembering that they need a warm, sunny spot with adequate drainage.
- Prepare a container and growing medium if starting indoors.
- Plant dahlia tubers, making sure to plant them the right way up, just below the surface of your growing medium.
- Mulch around the plants with an organic material.
| Difficulty | Easy |
| Equipment Required | Dahlia tubers, mulch, containers, compost |
| When To Plant | February to March (indoors), April (outdoors) |
When To Plant Dahlia Tubers
Dahlia tubers can be planted indoors early in the season in February or March or they can be planted directly into the garden in mid to late April, after the last frost date in your area.
The former option is best when space inside your home or in a greenhouse is available, as this will give dahlias a head start and allow them to get growing earlier.
1) Select & Source Your Dahlia Tubers
Of course, if you would like to plant dahlia tubers, then the first thing that you will have to do is select varieties and source some tubers of the dahlia varieties that you would like to grow.
“Growing your dahlia from a healthy stock is so important,” says David Hall from the specialist plant nursery Halls of Heddon.
“If the tubers don’t look right, appear stunted in habit or the leaves have severe mottling, then they may be affected by viruses and should be pulled out and removed.”
There are, of course, many different cultivars of this garden favourite that you might consider growing in your garden, with flowers in a range of styles, shapes, hues and sizes.
There are no fewer than around 120 dahlia cultivars that have an RHS Award of Garden Merit, so these reliable choices could be a good place to start when trying to select dahlias for your garden.1
2) Decide Where To Grow Your Dahlias
As well as thinking about which dahlia tubers you would like to plant, you should also consider where you would like to grow them.
Dahlias can work well in a range of beds or borders and some smaller dahlias can also potentially be grown in containers, which is where Elaine from Dachshund Dahlias grows hers:
“We grow all our dahlias in pots, as the tubers would be lost if they remained in the ground in our Scottish location.
“The ground is too wet and lacks proper drainage, meaning the tubers would rot.”
When choosing where to plant them, be sure to remember that dahlias need as warm, sheltered and sunny a spot as possible.
They will do best in rich, fertile soil or growing medium that is moist yet free-draining and can tolerate neither extremely dry conditions nor waterlogging.
3) Prepare The Containers
If you decide to start tubers indoors in pots to get a head start on the growing season, then you will have to prepare containers with a growing medium for your dahlia tubers.
“In some parts of the UK, dahlias can be left in the ground over winter, but in most areas, they will need to be dug up and stored,” shares Horticultural Consultant Colin Skelly.
“When replanting in spring, giving the roots a head start by potting and keeping in a glasshouse or cold frame makes a big difference to how fast they will establish once in the ground.”
Plant the tubers into a multipurpose compost that is peat-free or a homemade equivalent.
“If you are growing from a cutting or a dormant tuber, you will need to start off in a small pot and continuously pot on into the next size until you are finally using a 7.5-litre pot,” advises June Nash, from The National Dahlia Society.
“Use good quality compost and give an occasional feed.”
The size of the pots is not as relevant, as they will only be in the containers for a short time before you plant them out into their long-term containers or their positions in the garden.
However, good drainage is still important.
4) Plant Your Dahlia Tubers
When planting dormant dahlia tubers in pots of multipurpose compost in the spring or when directly planting them where they are to grow, make sure that you have them the right way up, with the uppermost linking area positioned just below the surface of the growing medium.
The shoots will appear from this area where the sausage-like tubers are linked.
If you are starting your dahlias in pots, you will then transfer these to their final growing positions outdoors after the risk of frost has passed.
When planting these dahlias out into your garden, they should again be planted at the same depth that they were in their containers, with the top of the tubers where the shoots grow from just at the soil surface.
For most dahlias, the tubers should be planted in the ground with a spacing of around 60cm between them.
Softwood cuttings can also be planted out at around the same time.
Rooted cuttings should also be spaced at 50-60cm apart, with the top of the compost in their pots just a little below the soil level.
Remember that there are larger and smaller dahlias and you should think about the size of the specific dahlia variety you are growing when determining plant spacing.
5) Add Organic Mulch
One final thing to think about after planting dahlia tubers outside, in the ground or in containers is that you should add an organic mulch around them to provide fertility, reduce moisture loss and suppress weeds.
Just make sure that the mulch surrounds but does not touch the stems of your plants.
References
1. Dahlia. (n.d.). Royal Horticultural Society. Retrieved March 29, 2023, from https://www.rhs.org.uk/plants/dahlia
