Dahlias are having their moment in the horticultural spotlight and whilst I’m a great advocate of growing what you love and what makes you smile, rather than what’s fashionable, the revival of this versatile plant is certainly welcome.
Available in a wide range of different colours, shapes and sizes, there’s a dahlia to suit every space. They bring a burst of extra colour and texture later in the season when other blooms have faded and are equally at home in a pot or in the ground, nestled in a traditional cottage garden or in a vibrant tropical oasis.
Dahlias are easy to grow and care for as long as you have a sunny spot for them but they don’t cope well with extremely cold, wet weather so will need protection over winter, more on that later.
Dahlias are perennial plants that will give you years of enjoyment and can be grown from seeds, cuttings and divisions but if you’re just starting out, by far the easiest is from tubers, which I will explain here.
Which dahlia to choose?
Although I’m always tempted to pick my favourite colours or shapes, the best advice for success is to choose a variety that suits your growing space and the amount of care you’re able to give your plant. It’s also good to consider the attractiveness to pollinators which much prefer the single flowered varieties which allow easy access to the pollen and whether you hope to be able to cut the flowers to also enjoy them inside your home.
A key consideration when choosing your dahlia is the size of space you have available and whether it will be grown in a container or in the ground. Shorter varieties are perfect for pots, planters, window boxes and the front of borders while larger varieties are best suited to the back of a border and will almost certainly require a support of some kind when they grow to full height.
Although you can grow the smallest bedding dahlias from seed, purchase rooted cuttings and of course full sized flowering plants in the summer, I find that tubers provide the best value and deliver the most reliable results.
Where to plant dahlias?
Following the advice above on size, dahlias do well planted in containers and in the ground if you are able to give them a sheltered spot that’s in the sunshine for at least 6 hours a day. They do not fare well in a mostly shaded environment and are unlikely to thrive.
Dahlias will grow in most soil types but you’ll get a more robust plant with the best flowers when planted in a rich soil that is moist but that drains freely. In continuous wet weather or in waterlogged soil, the tubers may rot and the plant would then die.
When planted in a light soil and protected from frost, the plant is more likely to survive the winter without having to be dug up, in heavy soils they definitely will need to be removed and stored, later in autumn.
With either option, starting them off in pots indoors is an excellent way to ensure that you can enjoy the flowers for more of the summer.
When to plant dahlias?
Dahlias need a warm, frost free climate to flourish so I find that where I live in the North of the UK, the best time to plant them is later in March and any time before the end of April, in starter pots in the warmth of the house, a nice sunny window sill will be perfect. If you have a greenhouse, better still and a grow lamp or heat mat will work well too but none of these are strictly necessary if you’re happy to wait for a week or two longer. Depending on the final position for your plant, you can then transfer it outside to either a bigger pot or directly into the ground after all risk of frost has passed – think of it as giving the plant a head start. If you’d rather not have plants indoors, or simply don’t have the space, then wait until mid-May before planting the tubers directly into the ground by the time the shoots break through the surface it will be June when the temperatures should have increased.
How to plant dahlias?
Some people like to soak the dry dahlia tuber in water for an hour before planting but I’ve not done this and find that as long as you water well after planting, it isn’t really necessary.
If you’re starting the growing process indoors, a large pot filled with peat-free compost will provide a good start for your dahlia. For planting outside, some rich compost added to the planting hole will help to feed the plant as it grows.
Make a large well inside your pot and gently place the tuber in, ensuring the string-like roots are at the bottom, the fleshy tuber is in the centre and the point at which the roots meet the woody stem is pointing upwards. Completely cover with soil, filling in all of the air pockets by gently firming the compost down.
Water well and allow the pot to drain before placing it in its bright, warm spot and then water regularly when the top few centimetres of the soil become dry.
Within about 4 weeks, you’ll see the shoots appear and when you are certain that the risk of frost has passed, it’s time to get the plants used to the outdoors by placing them outside during the day and bringing them back inside overnight, for about a week. At the end of this period, they can then be planted into the ground or a decorative pot or window box where they will carry on growing and eventually flower.
If you are planting straight into the ground, shorter varieties should be approximately 6cm deep and taller varieties, which need to be more firmly anchored, would benefit from being 15-20cm deep. For the taller varieties, it’s a good idea to insert a cane or support at the time of planting to avoid piercing the tubers when one is needed later, as the plant grows.
If you are growing more than one plant, nature’s natural pattern of odd numbers looks the most visually satisfying. It can be really tempting to pack them in when you have an expanse of bare soil but the plants will grow and become bushy so do just leave 20-30cm of space between the plants to allow air to circulate and to avoid crowding.
When you’ve completed your planting, water well and if you can, add a thick layer of mulch to help retain the moisture and protect the young shoots.
How to care for dahlias?
Slugs eating dahlias
Tasty new dahlia shoots seem to be a magnet for slugs so take some simple measures to give them a bit of protection using the tips here Slug Stopping Strategies
Watering dahlias
If the summer is a particularly hot one with little rainfall, your dahlias will need to be watered. A good soak, directed at the base of the plant, rather than a light sprinkle from above, will conserve water and ensure the plants roots get the moisture they need.
Deadheading dahlias
To keep your plant blooming all summer, removing the dead flower heads is really helpful. Look out for the pointed shape heads (the buds are rounded) and following the stem down to the next set of leaves, snip just above them. This will ensure the plant produces more flowers, rather than seeds.
Pinching out dahlias
If your plant looks a bit straggly or overcrowded, you can remove all but 5 sturdy shoots at ground level and using your thumb and forefinger gently pinch out the tip at the top of the shoot, down to just above the next pair of leaves. This will encourage bushy growth and lots of flowers.
Supporting dahlias
As your plant grows, gently secure the stem to the support with some loosely tied twine. This will prevent the stems falling over in the wind or bending under the weight of rain.
Feeding dahlias
Dahlias grow quickly and you can boost their vigour and flowering potential if you choose to feed them with some organic potassium or all-purpose fertiliser during the summer. Those in pots and planters that can’t stretch their roots further to take extra nutrients from the ground, particularly benefit from this.
Overwintering dahlias
The first autumn frost will kill off the dahlias remaining flowers and foliage. Where you live and your winter temperatures will dictate how best to ensure that your dahlias are protected over the winter.
If you live in an area with mild winters and you have a light, free draining soil that doesn’t get waterlogged, you may choose to leave them outside. If so, a covering of mulch will provide some additional protection. Learn more here Marvellous Mulching
Pots can easily be moved to a shed, garage or similar space for winter where there is no danger of them freezing.
Otherwise, you can dig up the tubers, shake off the excess soil, dry them out and store in a box with some ventilation holes, in a frost-free place over winter. Check them occasionally to make sure that they remain dry and if any tubers become squishy or rotten discard these.
I hope that you’ve found this advice helpful, although there are a few little chores involved with growing dahlias, you’ll be well rewarded with sensational flowers not just this summer but for many more to come. Next spring, you may even be able to divide your tubers to produce more plants that you can gift to friends and family or use to increase the flowers in your own garden. If this sounds interesting, Learn more here Divide and Multiply and please do let me know how you get on.
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