Rising stars
It’s time to wake up your dahlias from winter hibernation and prepare for a spectacular show this summer, says Monty Don
BACK in the 1980s, and even the 1990s, there were only a few dahlias that were at all acceptable to self-appointed arbiters of horticultural good taste, but thankfully we have moved beyond all that nonsense and I’d recommend that every garden should grow as many dahlias as they have room for. I certainly do.
Dahlias were discovered in Central America by Spanish explorers in the 16th century and later introduced to Europe. There were attempts to establish them as a food crop, along with other New World imports such as potatoes and tomatoes, but it was quickly found that while dahlias were, strictly speaking, edible, they tasted horrible. As a result, botanists focused on the plants’ decorative rather than nutritional qualities, breeding hybrids with more spectacular blooms than the species parents.
If you have very free-draining soil and live in the south, dahlias can be safely left outside, especially if they’re planted good and deep so they have an insulating layer of soil above them. But I have found that it’s worth digging them up and bringing them in under cover over winter, otherwise I lose more than the number that make it through to spring.
THE secret to storing dahlias is to cut off the stems with secateurs and then clean the tubers — removing any that are damaged and checking they’re not harbouring any slugs — before storing the tubers in a material that will insulate them and stop them drying out. In the past I’ve used spent potting compost, building sand, vermiculite and coir, but now it’s scrunched-up newspaper, which is a good way of recycling it and works extremely well. Then pack into crates and put them in a cool, dark but frost-free place; a cellar or garden shed is ideal.
However, it’s now time to bring them out of hibernation and prepare them for replanting. If you put them straight out into the border there’s a real risk that the new shoots will be nipped by a late frost, and although this is unlikely to rot the tubers, it means that you’re back to square one and flowering will be delayed.
It’s better that when you take the tubers out of their protection you start by checking them over, feeling them for firmness and discarding any that are either rotten or shrivelled. The latter condition — a result of being too dry — is more likely, and it’s a good idea to water the tubers once or twice in winter to keep the moisture levels up. Then pot up the tubers in a recycled plastic pot, using fresh peat-free compost so that they can grow strongly for the next month or two with as much protection as they need. Plant them out when all risk of frost has passed and when they are strong, with 30-45cm of stem and foliage.
This is also the time to prepare a few plants to provide cuttings. Pot them up so the tubers are only just below the surface of the compost, water well and place the pot on a heated surface. If you do not have a heated mat, a windowsill above a radiator will do fine. Keep them watered and in a week or two, they will produce strong young shoots. When these are about 8cm long, cut the strongest where they join the tuber. Put these cuttings into compost mixed with an equal volume of grit or perlite and place somewhere light and warm.
Water well and spray with a mister at least once a day. They will root quickly and can be potted on individually after a few weeks, then grown on as young plants to provide late flowers this summer and healthy new plants next year.