watering
Dahlias prefer a moist soil. In a drought, water them once a week and water with a good flood, not a gentle sprinkle. If your dahlias are in pots, water them frequently – every day during a drought. They are thirsty plants.
fertilising
If your dahlias are in pots, either use a slow release fertiliser or feed fortnightly with a liquid comfrey or seaweed fertiliser. Start after the first month.
staking
All dahlias should be grown alongside a stake. Make sure to continue to tie the dahlias 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.
deadheading
If you don’t pick every dahlia flower for the house, they will need regular deadheading, which will promote flowering. To deadhead, follow the flower stem down and cut above the first pair of leaves you meet.
propagating
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. Remove them with a clean, sharp knife along with a small portion of the parent tuber.
Remove all but the top pair of leaves and pinch out the tip.
Prepare a 1 litre pot with a mix of compost and grit (3 parts compost to 1 part grit). Place each cutting at the edge of the pot, with the leaves just above the top of the compost and spaced so that they are not touching.
Water from above to settle the compost. Then place somewhere light, but out of direct sunlight in a warm spot or in a heated propagator. Label the pot.
In about 3-4 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 has passed.
With regular feeding and watering, the plants grown from cuttings will flower later the same summer and form tubers.
overwintering dahlias
There are two ways of overwintering dahlias.
overwintering in the ground
In recent years, our winters in the south of England have been so mild that dahlias left in the ground, mulched deeply to protect them from the frost, have re-emerged fine, bulking up and flowering well before the other plants grown in pots. You could opt for this low-maintenance regime, but you risk losing your plants if we are hit by a hard winter.
If you go for this option, dahlias can be left in place and protected with a thick mulch on top over, which you can clear away once the worst of the frosts are over in the spring.
To do this, wait for the dahlias to get blackened by the first frosts of autumn, then cut them to within 10cm (4in) of the ground. Then put labels where the crown is showing – make sure each dahlia is labelled, as it’s so easy to forget which plant is where. Then add a mound (a whole bucket) of mulch over each one – if you bury them deep, it’s like giving them a duvet for the winter.
overwintering by lifting
The second way is to lift the dahlias out of the ground and store them undercover. This lifting method is advised if you’re growing dahlias in a mixed border, as dahlias left in mixed beds could become overshadowed by spring and summer growth.
when to lift dahlias
To be sure of conserving your plants for next year, lift your dahlias after the tops have been frosted in the autumn.
how to lift dahlias
Cut your dahlia plants down to 15cm (6in) before you dig them up. Knock off the surplus soil and, with a small piece of stick, scoop out the loose soil between the tubers – but leave enough to hold them in place.
how to store dahlias
Do not clean your lifted tubers under a tap; to get water on a tuber at this time of year often spells disaster. Turn the tubers upside down in a crate and leave to dry for a couple of weeks.
Then pack them away in shallow trays or in a storage box, surrounding the tubers with dry compost, vermiculite or dry sand, or alternatively wrap them in newspaper. This prevents the tubers drying out.
Store them in a cool, frost-free place – a cellar, attic or shed is perfect. Inspect tubers regularly during winter for rotting.
