How To Grow Dahlias

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Dahlias thrive in most sunny situations and do best in a fertile soil, with moisture and good drainage. They need winter protection and should be planted out when the danger of frost is over, usually May to early June depending on where in the country you live. Pot the tubers up undercover in March or early April, in a generous pot (at least 2 litre – I use 3 litre pots) filled with multi-purpose potting compost. Place them in a light, frost-free place and keep the compost moist. They will have formed bushy plants by the time the frosts have ended and will be in flower by the beginning of July.

Alternatively, wait until the risk of frosts is over and plant straight in to the ground with plenty of organic matter added to the planting hole. Insert a stout stick when planting the tuber (or plant) out as they will make sizeable plants when fully grown.

As they grow pinch out the growing tips once plants reach a height of about 40cm (16in) to encourage branching and remove all but five shoots sprouting from the tuber. There may be several more shoots, some of them weedy, but all but five must go. It feels brutal, but pinching out encourages bushy plants and with only five stems allowed to develop, you will get strong, vigorous growth that will produce lots of flowers.

Once a fortnight, feed them with a liquid balanced feed like Seasol. In a drought, it’s a good idea to water them once a week, with a good flood not a gentle sprinkle. With the stake in place at planting, 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. You will also need to protect your plants from slugs and snail damage.

There are two ways of overwintering dahlias; in mild winters dahlias can be left in the ground and protected with a thick mulch or alternatively, once the foliage has been frosted  you can easily lift them and bring them indoors to a cool but in a frost -free place. Once dry, store the tubers in shallow trays or crates and surround with compost, vermiculite or dry sand, just covering the tubers (leave the crown exposed). Inspect tubers regularly during winter for rotting.

How to grow dahlias in a pot?

Choose a container which is at least 30cm (12") in diameter and depth for optimum growth and plant one per container as they make large plants when fully grown. Use multi-purpose compost and add a slow-release fertiliser for strong growth. Plant tubers as deep as you would when planting in the ground and insert a stout support.

How to grow dahlias from cuttings?

Dahlias are easily propagated from basal cuttings. In the spring once the tuber has started sprouting, select strong, healthy shoots about 7.5cm (3in) long and remove them with a clean, sharp knife along with a small portion of the parent tuber. Remove the lower leaves and dip the base of the cutting in hormone rooting powder or liquid. 

Make a hole for the cutting in pot filled with suitable cutting compost using a dibber or clean, blunt stick and insert the base of the cutting with the first pair of leaves just above the level of the compost. Insert three cuttings per pot. Cover with a plastic bag held in place with a rubber band or in a heated propagator and place somewhere light, but out of direct sunlight. Label the pot and water it from above to settle the compost.

In about three-four weeks the cuttings will have formed roots, carefully pot each cutting individually into a 7.5cm (3in) pot and grow on, planting out after the risk of frosts. With regular feeding and watering, the plants grown from cuttings should flower later the same summer.

How tall do dahlias grow?

Dahlias range in height from the miniature 40cm right up to 1.5 – 2 metres. View our full collection.

To encourage giant dahlia blooms, remove all but 3 - 5 shoots from the tuber as it grows and once it reaches the flowering stage remove the side buds at the end of each stem so that the energy goes to the main bud. Feed regularly with a high potash, low nitrogen feed.

How to grow dahlias from seeds?

Dahlia seeds need to be sown between February and April undercover. Sow, 0.5cm deep, in trays of moist compost. Place in a warm position (15-20°C (60-68°F). Keep moist. Transplant seedlings, to other 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, May - June, spacing your plants 30cm apart, in well-drained soil and a sunny spot.