There’s one flower whose relevance in the zeitgeist fascinates me beyond all others: the dahlia. Bold, brash, blooms as big as your head, they can command devotion bordering on obsession among some flower-growers, especially – and intriguingly – among the relatively inexperienced gardener. This is, I think, because they can be straightforward to grow, and look good on Instagram. I suspect in some gardens dahlias have never been out of fashion. However, they’ve certainly enjoyed a prolonged moment over the past decade. A couple of summers ago, though, I chaired a panel with experts Sarah Raven and Arthur Parkinson, who admitted to being a bit fed up with the cream-coloured queen of Pinterest, dahlia “Café au Lait”. This, combined with their absence during the one-off September Chelsea flower show a few months later, had me convinced the dahlia’s millennial reign was over. Nevertheless, they persevere on Instagram – and life is too short to grow flowers according to trends. I mention all this because now’s the time to get cracking if you want flowers this summer (and autumn, and maybe even winter) and haven’t bought tubers. Dahlias begin as tubers: funny, potatoey and indeed edible little rhizomes indigenous to Central America, where they were a food crop before European colonists turned up. The Aztec name for them is acocoxochitl, which refers to the stems’ abilities to carry water. In the UK, those who ordered their dahlias last year will have received them a couple of months ago. More assertive gardeners will have planted them in pots, kept them ever so slightly moist – they are prone to rot – and somewhere warm and bright, such as a greenhouse (or my south-facing front room). Last year, I planted tubers in pots outside in mid-May. They leafed up quickly and, while I didn’t have the world’s greatest display, I did get some flowers. Better, then, at this time of year, to be picking up ones someone else has started off for you. Nurseries such as Halls of Heddon, which has marked its 60th anniversary by going peat-free, will dispatch “mini plants”, which can be planted into 12cm pots around now – and garden-ready dahlias from June. The arrival of its catalogue in the depths of December is one of my favourite annual traditions, the combination of old-school graphic design, bright colour and preposterous variety names (‘Crazy 4 Don’, ‘Deborah’s Kiwi’) brightening up long nights. If you’re shopping for varieties for the first time, make sure to check the height as much as the colour: dahlias can be big plants that need staking as the season goes on. After a couple of summers of deadheading and preening, I’m keeping any I grow in pots (‘Waltzing Mathilda’ is lovely against autumnal sunlight, ‘Moonfire’ has chic black stems and ‘Tally Ho’ is imbued with retro charm), where they won’t take up too much space for other perennials. I’m sure I’ll see plenty on the ’gram.