Easy to Grow Dahlias
Dahlias are easy to grow and in a good year produce flowers from late June to early December They come in all shapes and sizes, and are available in most of the best flower colours. They are wonderful for filling gaps in borders and make excellent cut flowers.
Soil and Site
Dahlias thrive in most sunny situations and do best in a fertile soil, with moisture and good drainage.
Dig a hole at least 30cm square and 30cm deep for each one, spacing each dahlia tuber 75cm apart (depending on expected final size of variety).
Planting from Tubers
Dahlias are tender tubers. Their root structures look like a bunch of salamis gathered together on a stem. If you plant them out before the frosts are over, they may get frosted and die, so pot them up 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.
Choose a container which is at least 30cm (12″) in diameter and depth for optimum growth. 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.
Keep in mind that all dahlias – even very healthy and long-standing old ones – grow at hugely different rates. Not all dahlias grow quick and fast and often more interesting varieties are slower, more delicate growers.
Whether you have raised your dahlias outside in the garden or under cover, you need to pinch out the tips of the main shoot as they grow. Either with a sharp knife, or squeezed between your thumb and forefinger, remove the main shoot down to the top pair of leaves.
You also need to 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.
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 on in pots. You could opt for this low-maintenance regime, but you risk losing your plants if we are hit by a hard winter.
Earwigs can be a problem with dahlias, eating the flowers and the leaves. The organic way of control is to position pots filled with straw upside down raised on canes dotted throughout your dahlias. The earwigs crawl into the straw in the heat of the day. At the end of the day you can bag them, burn them or release them somewhere else far from your dahlias. Slugs also love dahlias, especially when they first shoot, so protect them from the word go.
Only pick dahlias in full flower. Re-cut the hollow stem ends under water to avoid airlocks.
If you don’t pick every flower for the house, it’s a good idea to have an occasional blitz of deadheading. This will make them look much better and will prolong flowering. Cut heads off, removing the whole dead flowering stem.
Dahlias can also be bought as plants in late spring and summer