Growing dahlias with Sarah Raven
For two decades, since the publication of her first book, ‘The Cutting Garden’, Sarah has led the way in introducing a new kind of productive gardening. Her aim, to create intense colour and beauty combined with a practical and easy to achieve approach. Her love of gardening extends to all areas, from growing cut flowers and delicious vegetables from seed, to designing gardens packed full of incredible colour and scent every season. Always with an eye to creating environmentally friendly havens for birds, bees and other pollinators. Tracing the year from January to December, Sarah’s new book ‘A Year Full of Flowers: Gardening for all seasons’ provides inspiration, planting ideas and expert advice for a beautiful garden all year round. She is a teacher, broadcaster; has a popular gardening podcast ‘grow, cook, eat, arrange, and runs sarahraven.com, (with over 600,000 customers).
Dahlias
Dahlias are some of the lowest maintenance, highest production cut flowers and garden plants you can grow. Here at Perch Hill, we grow hundreds and hundreds of dahlias, and they are the highlight of the summer and autumn garden. Excellent cut for a vase, each dahlia tuber can produce hundreds of flowers, meaning a colourful show inside and out for weeks on end. They come in all different sizes and colours, each as exciting as the next, but they also come in myriad shapes.
Sowing dahlia seeds
Dahlias are commonly started into growth as tubers, as this is a faster and often more reliable way to grow them, but it is possible to grow dahlias from seed.
Dahlia seeds should be sown between February and April undercover. Sow 0.5cm deep in trays of moist compost. Place in a warm position, about 15-20°C (60-68°F). Keep moist.
Transplant seedlings to deeper trays or individual small pots when large enough to handle.
Grow on in cooler, but frost-free conditions. Gradually harden off young plants before planting out after the risk of frost has passed in May and June.
Planting dahlia tubers in pots
Dahlia tubers can be started into growth in March or April in pots undercover, and then planted out in the garden in late May and June.
Start by half-filling a 2 or 3 litre pot with peat-free multi-purpose compost. Place the tuber in the pot with the central stem upwards and cover with more compost. Don’t forget to label and lightly water the pot, then place it somewhere warm and frost-free – a greenhouse is ideal. Don’t water again until they start to shoot, and even then only water lightly.
After 2-3 weeks, shoots will start appearing – some varieties may take a little longer. As these shoots grow, pinch out the tips of the main shoot (you can use a sharp knife or a squeeze between your thumb and forefinger), down to the top pair of leaves.
As the plant starts to grow further, remove all but five shoots sprouting from the tuber. This will feel harsh, but by having only five stems, this will allow each stem to develop, grow strong and vigorous, and the result is lots of flowers!
Planting dahlia tubers in the ground
If you don’t have space to plant the tubers in pots first, you can put them straight into the ground in spring – just make sure the frosts are nearly over.
Plant the tubers just under the soil surface and ensure they are approximately 75cm (30in) apart, depending on variety.
Insert a stout stick to act as a stake when planting as they can make sizeable plants when fully grown. Mulch over the top of them or protect them with a cloche or horticultural fleece. This is particularly important if the foliage appears before the frosts are over.
Whether you have raised your dahlia tubers outside in the garden or undercover, you need to pinch out the tips of the main shoot once three pairs of leaves have grown. You can use a sharp knife or a squeeze between your thumb and forefinger, and pinch out down to the top pair of leaves.
Planting dahlia plants
If you have a dahlia in a 2 or 3 litre pot that you’ve grown from a tuber or bought as a plant, you can plant it outside once the risk of frost has passed in spring. Dig a planting hole for each plant in a sunny, sheltered position.
The hole needs to be at least 30cm (1ft) square, 30cm (1ft) deep and the plants should be spaced approximately 75cm (30in) apart, depending on variety. Add plenty of organic matter to the hole. On heavy clay, add grit to the planting hole. Place the dahlia in the hole with the tubers just below the soil surface and fill in around the rootball.
Insert a stake when planting as they can make sizeable plants when fully grown. You will need a stout stake (not just a bamboo cane) to support each plant and it is a good idea to knock this in first and then place the plant by its side.
As they grow, pinch out the growing tips once three pairs of leaves have grown to encourage branching.
With the stake in place at planting, you can continue to tie them in every couple of weeks. Dahlias grow very quickly once they get going and can easily break off right at the base in wind or rain if they are not securely staked.
Growing dahlias in a pot
Dahlias are usually started in pots undercover and then planted out in the garden, however it is possible to grow dahlias in a pot. Make sure you choose a slightly compact dahlia variety, as some dahlias can grow over 1.5m (5ft) tall. Then choose a container which is at least 30cm (1ft) in diameter and 40cm (15in) deep for optimum growth. Use peat free multi-purpose compost and add a slow-release fertiliser for strong growth.
Plant dahlia tubers and plants as you would when planting in the ground, just under the surface of the compost. Then add a stake, a label and water well.
If you’re starting dahlias into growth in March or April, place the pot somewhere light, warm and frost-free. If you’re starting in early summer, simply leave the pot outdoors.
Photography © Jonathan Buckley
Visit sarahraven.com/podcast to listen to Sarah’s podcast ‘grow, cook, eat, arrange’
Sarah Raven at Thyme
We are delighted to announce that Sarah will be hosting three gardening courses at Thyme in October. From learning the art of gardening in pots with with fellow gardener Arthur Parkinson, creating a cutting garden of your own, or for the general gardener, who - like Sarah – adores and thrives on year round colour, scent and floweriness just outside the door, be sure to book you spot.
