Dahlias have gone from being inexplicably out of fashion to one of the most on-trend plants around in the space of a mere five years or so. However, as often happens with plants that have enjoyed a renaissance, some of the horticultural advice that comes with them is a little outdated. This includes the single trickiest thing about these wonderfully blousy blooms – lifting them around this time of year.
If you’re new to growing dahlias, here’s how to reduce your workload and get better results at the same time.
From the highlands of Mexico, dahlias are often thought of as desperately tender specimens – a belief which is reinforced by the fact that their flowers, leaves and stems are rendered a blackened, soggy mush pretty much instantly at the first hard frost. At this point, traditional advice is to carefully lift the plants’ swollen roots, dust off the soil and store them in a cool, dark space, like a garage or shed. This is a tricky practice, not just because of the hefty digging, mess and faff involved, but also because many of the tubers are damaged in the process. Any roots sliced during lifting will quickly rot in storage and, even if these are carefully separated, can succumb to rot, or dry and shrivel. This can even happen to fully intact tubers meticulously stored. All this is, of course, imagining that you have a cool yet frost-free, dark but well-ventilated area in your house with plenty of storage space. Not so easy if you only have a tiny patio or balcony on which to grow them.
Happily, the tubers of dahlias are really far more cold-hardy than tradition would have us believe. Insulated from the lowest temperatures by the soil they are buried in, they will easily take air temperatures as low as -10C. This covers most of the UK, with the exception of record winters or places in the far north. A 15cm-thick layer of organic mulch, such as bark, leaf mould or compost laid over the base of these plants adds a protective layer like an insulating blanket, and over time it will break down to improve the structure of the soil and add essential nutrients.
So why do we still do it? It may simply be because of the misplaced assumption based on their exotic origin – many perfectly hardy camellias were grown in glasshouses for centuries before we discovered this wasn’t necessary. Maybe it’s because Victorian gardeners often grew dahlias as cut flowers for shows, and lifting and planting them indoors allowed an earlier season start. Or maybe it’s a function of global warming. After all, these plants did start to become popular in Britain during a mini ice age that ended in the mid-19th century. Whatever the cause, most gardeners are likely to get better results by just not bothering.
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