I planted 23 different varieties of dahlias yesterday – mostly pinks, purples, magentas and reds, with a couple of white and peach varieties thrown in for good measure. A week ago, and not too far from here (about two turns left and one turn right), I journeyed the neighbourhood and spied two fully grown dahlia plants already flowering their socks off. If they could thrive not five minutes away from my own doorstep, it was high time I planted my own.
Dahlias are one of the most prolific flowering perennials and come in myriad shapes and sizes, from neat-as-a-pin pompoms to spidery cactus types and paeony and water lily lookalikes. The flowers range in size from tiny-tot heads less than 50mm to giants with a diameter of over 250mm.
Condition your soil
Plant your dahlia tubers once all risk of frosts has passed. September is a good time to plant tubers, but leave it until October if you often experience late frosts.
Choose a sunny spot with free-draining soil. Dig over the soil and incorporate compost (ideally you should do this a few weeks before planting). Avoid using fresh manure or compost that hasn’t quite broken down as these can cause excessive soft growth which is susceptible to mildews and stem rot.
Dahlias are heavy feeders, so incorporate a balanced fertiliser such as Nitrophoska Blue at planting time, or apply a good dressing of blood and bone. Apply this 10-14 days before planting your tubers.
Plant the tubers so that their necks are 5-6cm below the soil. If tubers have already sprouted, position them so the base of this growth is just below soil level. Scatter slug and snail bait around the plants too as those pesky molluscs love to munch on the sprouting tips.
Tall dahlias will need staking, or there may be tears and tantrums if you find all your flowering stems flattened after a night of rain and high wind (try to avoid windy spots though). Insert the stakes at planting time to avoid root damage later.
Water when necessary, but don’t overdo it. Too much water can cause root rot.
When your plants reach about 30cm high, nip out the centre to encourage them to branch out and provide more flowering stems. Tie the plants to your stakes too as they grow, starting when they’re just a little over 30cm.