The Dahlia flower represents dignity, elegance and a commitment and bond that will last forever. They are therefore ideal cut flowers for celebrating love and marriage and we use them extensively in our wedding and celebration flowers (www.honeypotflowers.co.uk).
At this time of year (March) we begin to dust off the overwintered dahlia tubers and start them into growth. As they flower from June until the first frost blackens the leaves, the once unfashionable Dahlia creates a wonderful summer and early autumn show throughout the flower garden.
The choice of colours is unrivalled and ranges from white, red, pink and purple through to yellow and orange with many shades in between. Equally there is a huge range of sizes and forms ranging from less than 10cms in diameter to the huge and rather unwieldy ‘dinner-plate’ varieties at over 25cms. Breeding programmes have created many forms which now include singles, waterlily, collerette, anenome, pompon, ball, semi-cactus, cactus, decorative, orchid, and peony flower types to name but a few. There is probably a style, size and shade to meet just about every colour theme and requirement.
Origin
Dahlias are tuberous perennials originating from the uplands and mountains of Mexico and central america. The edible tubers were reportedly grown as a food crop by the Aztecs. As they are mostly unscented they attract pollinating insects through their bright colourful flowers.
Starting Dahlias in the spring
There is no doubt that growing high quality Dahlias takes some time and effort, particularly if you want to maintain and develop your investment in plants over a number of years. At this time of year we bring out the dahlias that we lifted last autumn and overwintered in our flower studio. Although some will perish we find that the majority will survive if the tubers are cleaned and air dried and then individually wrapped in newspaper in covered trays and boxes. Because we have got rather carried away over the years we now have so many tubers we just don’t have the room to lift and store every plant. We therefore allow some to take their chance in the garden covering them with straw and cloche plastic over winter. (We have written about how we do this in a previous article)
In March we check over the lifted tubers for any rot. If the damage is not too great it is often possible to remove one or two diseased tubers from a larger clump and they will still grow well.
The tubers are planted into individual large pots or crates in moist compost before bringing into a warm (15-18 °C) and light place indoors to encourage them to shoot. It is important to pinch out the tips of shoots once they begin to get going. This will help the plants to bush up and make a better shaped plant as well as reducing the risk of damage when you come to move the plants into the garden.
Propagation by division
There seems to be a difference of opinion on when to divide tubers if you want to split large clumps to create more plants. The RHS indicate that this should be done in the spring whilst others (eg. Floret Farm) advise that it is best done after lifting in the autumn. The important things to remember is that each portion must have a flower shoot and roots if it is to grow on and develop successfully.
This year, purely for practical reasons, we divided in the autumn. The clumps had got so large that they were difficult to effectively lift, clean and dry off before we set them down for the winter.
Taking cuttings
It is possible to take cuttings from your overwintered dahlias once the tubers have sprouted and the shoots are ≥2 inches long. This is again an excellent way of multiplying up your favourite varieties. We place the cuttings in small 3 inch pots of a free draining mix of multi-purpose compost and perlite (3 to 4 cuttings round the edge of each pot), water in, cover with a plastic bag and place on a warm window sill. They will root in just a few weeks if looked after. Once roots have formed we would then begin to remove the plastic cover slowly allowing some air into the bag for a few days before removing completely.
Soon you will have far more plants than you know what to do with and you can share with your friends!
Planting out
Dahlias can develop into large plants if they are grown well and need to be spaced at least 18 inches apart. Ideally they like to be planted in full sun with ground that retains moisture but is also well drained. On our wet clay soil we tend to plant on slightly raised beds to provide better drainage. We only plant out the growing tubers when all risk of frost has passed. However, you do sometimes get caught out and keeping some horticulture fleece at the ready to quickly throw over the plants to see them through a late cold snap is usually sufficient.
To get strong, lush plants that flower freely all year you need to water well and feed regularly. The RHS suggests feeding with a high potash liquid feed every 2 weeks from July to early September. I have to admit that regular feeding is not one of our strengths. Let us just say we are now better than we used to be!
Most of our Dahlias will need to be staked and supported at some point to ensure we get good straight stems that we can use in our bouquets and arrangements.
Pests to beware of
One advantage of starting the tubers indoors is that the plants are big enough to cope with the onslaught of slug and snails.
For those we leave in the ground the challenge is greater. You do really have to keep on top of them until the new shoots get away. Tidy up any old bricks, stones and straw where slugs and snails can hide during the day. A regular dose of biological control nematodes ( eg. Nemaslug) can also help. We are also delighted that the flower garden is home to toads, frogs and newts and keeping some longer, moist grass areas in the flower garden seems to encourage them.
Later in the year the battle will be with earwigs which will damage the leaves and eat the flowers. Interestingly we have found that white Dahlias seem to be particularly tasty but we don’t know the reason behind this.
Photoperiod
Armitage and Laushman report that day length has a direct influence on both flowering and tuber formation. Long days of 14 hours cause faster flower initiation but day lengths below 11 hours and greater than 16 hours have a negative impact. Short days (12 hours or less) result in tuber formation.
Breaking tuber dormancy
For many growers one of the reasons for lifting tubers in the autumn is to protect them from excessive cold temperatures over the winter. It is interesting to note that cold temperatures (around zero degrees centigrade) are however important in breaking tuber dormancy (Armitage and Laushman).
Cutting and conditioning
Dahlias can make spectacular cut flower arrangements if harvested at the correct stage and conditioned properly.
If the flowers are cut too early Dahlias buds often fail to open effectively. Equally you want to cut the flowers before the outer back petals begin to show signs of age. Petals will drop rapidly if the flowers are too old and so picking the flowers when they are at around 75% open is ideal.
The ideal time for cutting is in the early morning before the summer sun gets going. It is a lovely time to be out there in the flower field with your secateurs. The flowers once cut should immediately be placed into deep warm water and left to condition for a couple of hours. We use ‘flower food’ to increase vase life and some growers (see Linda Beutler) also advocate hot water treatment prior to placing in cool water.
We have noted that some varieties are more suitable for picking than others. For some varieties the flower will ‘shatter’ as you reach forward to cut them! We have found variety ‘Wizard of Oz’ particularly prone to this. Good for petal confetti however!
Treated well, Dahlias will give you months of pleasure throughout the summer and into the autumn months. The more you cut the more they will flower and it is important to keep on top of the dead heading to keep them flowering freely.
As the season progresses will will share some further pictures of the star blooms of the summer. Early spring is such an exciting time of year planning for warm summer days to come!
Further Reading
“Cut Flower Garden” by Floret Farms (ISBN 978-1-4521-4576-1)
“Specialty cut flowers” by Armitage and Lushman (ISBN 0-88192-579-9)
“Garden to vase” by Linda Beutler (ISBN 978-0-88192-825-9)
Honey Pot Flowers are wedding and celebration florists based in Warwickshire in the United Kingdom specialising in natural, locally grown seasonal flowers. We grow many of our own flowers allowing us to offer something very different and uniquely personal.
We are out in the garden ... 