COLUMNIST: OLIVIA THOMAS
Dahlias are tender and do not even get growing in the UK until late spring, so they flower in mid to late summer, and generally keep going until the first frost. We are not talking here about the smaller bedding varieties - dahlias grown for cutting have long stems and come in a huge variety of colours and shapes. They can create impact in an arrangement even in small numbers and can produce large numbers of stems from a single clump of tubers, which makes them very useful for home growers.
There are at least three different ways to grow dahlias: from tubers, cuttings, and seed. Mostly they are grown from tubers, which are sold as clumps that look a bit like ancient potatoes. The plant will grow more of these tubers over the course of the season and they can be divided in the autumn to increase the number available for growing next year.
Plants grown from tubers will be an exact clone of the variety. Cuttings taken from tubers started off indoors early in the season will also be a clone. Seeds, however, will vary from their parent plant, so you never know what you will get, but this is part of the fun!
If you are reading this issue in real time it is too late to start dahlias for this season, but keep this to come back to next spring.
Due to their tender nature, dahlias can be a bit precious, but do not let that put you off. The tubers need to be stored somewhere cold but frost-free over winter. I keep mine in a big plastic box in the shed, and bring them in the house if it threatens to get significantly below freezing in there. You can store them in sawdust or sand or wrap them in clingfilm. The idea is to stop them from freezing and then rotting but to keep them cold enough to stay dormant until spring.
In late spring, it is time to start the tubers off. Many people start their tubers directly in the ground, but young dahlia foliage is the snack of choice for slugs and snails, and any dahlias I have put straight in the ground have always been munched.
I start my tubers in the greenhouse in medium sized pots with minimal watering until they show good growth. The aim is to grow healthy, moderate-sized plants before putting them out, the larger and stronger the plant, the better they can withstand slug attack. This is the only anti-slug measure I take at the flower farm and in my cutting garden.
Once they are ready for the ground, prepare some rich soil, with plenty of compost if required. Do not plant them out before the last frost date in your area - here in South Ayrshire that will be around mid-May, but make sure you know your own area.
When growing for cut flowers, the aim is to have the best quality stems rather than the most in number. This means getting the plant to channel its energy into a smaller number of flowers.
Each tuber should just be allowed to produce 5-7 shoots, take off any others which can be used for cuttings if you wish. Once there are three or four sets of leaves on a shoot, take off the set of leaves at the tip (pinching out), which will encourage side shoots to grow on the stem. As the stems grow, you want just one bud per stem, so be ruthless about taking off any buds further down the stem – this will give you bigger, better flowers that are easier to arrange.
Once cut, dahlias do not open much, so when you pick look for blooms that are just fully open. Pick far down the stem to encourage the plant to throw up new long stems. As always, when picking cut flowers, harvest either first thing in the morning or in the evening. Put the stems into cold water in a dark, cool place for a few hours, ideally overnight, to rehydrate before arranging. Deadhead any that have gone past their best.
After a frost or two, when the leaves have started to blacken, cut all the stems and foliage back to the ground. If you live in a milder area, it is possible to keep the tubers in the ground over winter with a good mulch on top, but for most of us here in Scotland you will need to lift them out of the ground for storage. This is the point at which you can divide the clumps to increase your stock for next year.
Dahlias come in a very wide range of floral forms and sizes. The larger varieties in particular are perfect for displaying as a single stem, and the dinner-plate types really can be as big as the name suggests! Scatter them in bottles or tall thin vases throughout the house, or group them together for interest and impact, particularly varieties with similar shapes or tones.
In arrangements, the bigger varieties will be the focus. When you are deciding on varieties to grow, choose some with smaller flower heads that can be the supporting artists as well.
Also think about the fillers that you will be growing. It is important to have some that are either grown in succession to keep a supply of good flowers coming all season, or pick plants that are at the best in late summer - try Cosmos, multi-headed sunflowers (Helianthus) or coneflowers (Rudbeckia).
If you have been inspired to get growing, then here are a few of my favourite Dahlia cultivars to look out for:
‘Linda’s Baby’
‘Jowey Winnie’
‘Cafe au Lait’
‘Labyrinth’
‘Schipper’s Bronze’
I’d love to see your favourite dahlias so do get in touch on Instagram.
Olivia Thomas grows flowers that are better for people and the environment. Her passion is for sustainable floristry, for growing local flowers that she sells to florists and other businesses including cafes, bars, and restaurants, and locally to the public whenever there are enough flowers available!
See more of Olivia's beautiful blooms on her website, Instagram, and Facebook pages, or catch up with all her news on her Substack.
