Lift or leave dahlias? Anne’s advice
Is it better to lift dahlia tubers to store frost-free, or leave in the ground under mulch? Anne Swithinbank explains
WHETHER they are considered in or out of fashion, dahlias are hard to deny. By autumn, they have reached full size and are proving their worth as late-season performers.
They are also fuelling their tubers for next year, before stems are blackened by the first severe frost. At this point, the gardener has to decide whether to lift the tubers to store frost-free during winter, or leave them in the ground under a deep mulch. In colder regions, lifting is best – but in milder areas, it could be another 10 years before frost penetrates the ground sufficiently to cause damage.
Dahlias that are staying put will disappear without trace, so mark their spot with a cane or crab pot of twiggy sticks. This saves them from accidental damage from forks and spades, and also alerts you to emerging growth in spring.
Pale, tender shoots are like caviar to slugs and snails, so from March, set up a few slug pubs, grapefruit skins or lettuce leaf traps to see if they are around – and consider surrounding any vulnerable growth with wool pellet barriers. If you decide to use ferric phosphate slug pellets, just a few hidden beneath a pot will do the job.
Originally from Mexico and Guatemala, dahlias were believed to be used by the Aztecs for food and medicine. They were discovered by Francisco Hernández de Toledo who, as physician to Philip II of Spain, was sent to Mexico in 1570 to study and report back on its natural world. This task kept him busy for seven years, and he described two varieties of dahlias:
D. pinnata and D. imperialis. The first plants grown in Europe were at the Royal Botanic Gardens of Madrid in 1789.
Since those early days, we now have thousands of dahlia cultivars, with blooms varying in size from 2in (5cm) to 12in (30cm), and plants from lowly bedding kinds to large, border-filling cultivars, 5ft (1½m) tall or more. Some have bronze foliage, and there are dainty singles, those shaped like waterlilies, peonies or anemones, drumstick-like pompons, balls, quilled cactus-flowered cultivars and decoratives.
If you like a challenge, home in on the species dahlias. The tree dahlia
(D. imperialis) will grow to 8ft (2½m) and bears beautiful single pink or white flowers, 4in (10cm) across. Meanwhile, the tall d. coccinea has fern-like foliage and small orange-red flowers.