Tubers are the roots of mature plants and look like a cluster of brown, carrot-like roots joined by the previous year's dried stem. You can buy them from garden centres or by mail order in spring, or use your own tubers that have been overwintered.
When to plant dahlia tubers
Starting dahlias in pots is a great way to get them into growth earlier in the season. Simply plant dahlia tubers in large pots filled with peat-free multi-purpose potting compost in March or early April, and then keep them on a windowsill or in a frost-free greenhouse until late May, when it's safe to plant them outside.
Starting off dahlia in pots will also encourage them to develop more quickly, so they're likely to start flowering earlier. Before planting, soak the tubers in a bucket of tepid water for an hour so they can fully rehydrate.
Growing dahlias in pots
Many variteies of dahlia can be grown in pots all year round, providing a splash of colour on patios and balconies. Small to medium-sized dahlias, such as mignon and ruff dahlias, as well as slow-growing water lily, ball and pompom dahlias, do well in containers. Avoid growing cactus dahlias, which can grow to over 2m in height – as a general rule, only grow dahlias which don't usually require staking.
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Grow potted dahlias in a warm, sunny and sheltered spot, protected from strong winds. Water regularly and feed with a phosphate-rich liquid fertilizer once a week.
Use free-draining, peat-free compost and plant the tubers about halfway down, so that the buds on the tuber shafts are only lightly covered with soil. Water well. Pinch out the shoots when they're around 10cm long, to encourage bushy growth.
In winter, potted dahlias can simply be moved to a frost-free spot, such as an unheated greenhouse. Then, in spring, remove as much compost from above and around the tubers as you can, and replace with fresh compost. This will give the tubers a fresh burst of nutrients necessary for the best possible display.
Where to buy dahlias online:
- Crocus - Choose from a huge range of colours and shapes, and take advantage of discounted prices if you buy multiple collections of dahlia tubers
- Thompson & Morgan - Shop the new 2022 range of varieties, including ‘Electro Pink’, which is the world’s first dark leaved cactus dahlia, as well as the dwarf ‘Lubega Power Tropical Punch’ that’s ideal for containers
- de Jager - Established bulb specialists with an impressive collection of dahlia tubers, in a range of colours and flower shapes
- Dobies - Great selection on offer, with offers and discounts on specific collections
- Sarah Raven – great selection with lots of different varieties
You Will Need
- Dahlia tubers
- Large pots
- Peat-free multi-purpose compost
- Plant labels
Total time: 30 minutes
When planting dahlia tubers, ensure the joint where the roots meet the stem is facing upwards. Label your pots and grow on in a greenhouse or sunny windowsill. Keep the tubers well watered.
Pinch out the tips of the main shoot, down to the top pair of leaves. You also need to remove most of the shoots growing from the tuber, except for five. This encourages bushy plants, strong, vigorous growth and a lot more flowers.
When all risk of frost has passed, harden off your dahlias by placing them outside during the day and bringing them in at night. After a week they will be ready to plant out into their final growing positions.