Don’t give up on dahlias
The dry summer has left many dahlias struggling, says Monty Don – but there’s still time for them to shine
THIS summer’s been a poor one for my dahlias, but I live in hope. There’s another month of possible flowering for them to regain lost ground and shine in autumnal glory. However, in almost all previous years my garden has been rich with dahlia flowers from midJuly, and they should now be at their very peak.
The problem hasn’t been one of heat – dahlias like it hot – but dryness. Although the pots have been watered thoroughly and our soil is very moisture retentive, the drought has meant that many varieties have been very slow to form flower buds, despite the plants apparently growing normally. I think the timing of this has been significant because we often have a very dry September but that does not seem to inhibit flowering at all. It was the drought of June and July that stopped them in their tracks with the plants conserving energy.
What is really interesting is that it seems to have affected different varieties and colours in different ways.
I stress this is an unscientific, random observation from my own garden, but I do grow hundreds of dahlias across about 25 different varieties. For example the fabulous ‘Chat Noir’ has flowered abundantly, producing deep maroon and burgundy flowers held on tall stems, almost oblivious to the heat, whereas the normally profuse orange and apricot blooms of ‘David Howard’ hardly appeared at all until the beginning of this month.
Those that flower early and with richer, darker colours seem to have done better than the later-flowering varieties and especially those that are paler.
My pair of large orchard beds, flanking a long path, rely heavily on the huge ceriseand-white flowers of ‘Rothesay Reveller’. I have about 30 of these running along the whole length, dominating that part of the garden through August and September – but this year there’s been hardly a single flower from any of them.
But so much for the doom and gloom. The plants are all healthy and will survive to flower another day. I deadhead our dahlias almost daily to stop them setting seed and to keep the new flowers coming for as long as possible. It can be hard to tell a bud from a used flower, but the easiest way is to look at the shape. An unopened bud is always rounded, whereas a spent flower is always more or less conical. I always cut right back to the next bud or leaf on the stem – which can often be a fair way – otherwise you end up with the new flowers appearing among a bristle of dead stems.
Eventually frost gets them all and blackens the leaves to rags. It’s a mistake to ‘protect’ them from the first frost, as the tubers grow a lot in the early days of autumn and a light frost does not penetrate the soil to harm them, so bringing them in too early will be at the price of next year’s display. The longer the foliage can feed down into the tubers the bigger they’ll become, and large, plump tubers mean a healthy plant with lots of flowers the following season.
But around Bonfire Night I’ll dig up all the dahlias in beds and empty out those in pots, trim the foliage, remove excess soil and store the tubers in crates packed with spent potting compost (sand, coir or vermiculite also work well). These will then be placed on shelves in a cool but frost-free, dark place, where they spend the winter.
If you live in a warmer, drier part of the country you can keep your dahlias in the ground, but if you have heavy soil like mine that combines cold and wet, it’s best to play safe and lift them to protect them from rotting.