Looking at Dahlias you simply cannot help but admire their floriferous display. One of my favourite flowers for the Summer border, the beautiful South American native has so many faces. There are about 57,000 RHS registered cultivars of Dahlia and it is generally the hybrids that are available as garden flowers. The RHS lists fourteen groups of Dahlia and these are grouped by their flower shape. From simple open shapes to elaborate, almost geometrically perfect pom-pom configurations there are endless shapes, colours and cultivars to choose from for your garden. But before we look at these from a design point of view, let’s explore their interesting history.
These tuberous perennials hail from Mesoamerica- and are native to Mexico but they can also be found growing in Honduras, Nicaragua, Guatemala, El Salvador and Costa Rica and in 1963 the plant was declared the National Flower of Mexico. Varieties of this flower were first discovered by Europeans when King Phillip II of Spain sent Francisco Hernandez, a physician to the crown, to Mexico to study plant life and the bountiful resources of the country. Interestingly one of the first varieties of the plant that his team came across was the Tree Dahlia-Dahlia imperialis- which has huge hollow stems which can grow up to over 6 metres in height. The Aztecs named this plant ‘Cocoxochitl’ which translates as ‘Water Cane’ or and this was due to the fact that the stems were hollow and could be used to transport water for Aztec hunters. The plant was also used as a source of food and the Aztecs gathered it from the wild and also cultivated it themselves. It was also interestingly used for many medicinal reasons, among them to treat Epilepsy.
Even today the Dahlia is a staple ingredient in Oaxaca cuisine and is grown for the large tubers-reminiscent of sweet potatoes- as well as being used for producing Dacopa, an extract using roasted tubers whose intense mocha like taste can be used to flavour beverages.
In the garden, dahlias are such wonderful plants. The Dahlia maxi in the main picture here is a new breed that is incredibly strong and visually stunning. Available in many colours, the flowers are beautifully shaped pop-pom shaped flowers which are so perfect they almost seem unreal. The abundance of flowers on one plant is another major plus and I love how when one flower stops blooming many more soon follow to keep the plant looking fresh and full. Keep in mind, for the best display dead-heading here is essential.
Having said that, one must keep in mind-Dahlias are not the simplest plants to grow. The tubers should be lifted at the end of the season and stored in a dry dark place over Winter so that are not killed off by frost. This makes them a plant that requires more maintenance than some other perennials. Most people who love these plants will agree that the role this plant plays in the border is well worth the effort and I have seen many people fall in love with these specimens once they flower.
They really are a fabulous plant to scatter in the garden for pops of colour where there may be a gap. One other thing to look out for here is slugs- Dahlias can be totally destroyed overnight if not protected, particularly early in the seasons when the leaves are still emerging and soft. I like to scatter a few copper coins around the base as slugs don’t like copper!
RHS grouping system
With so many cultivars to choose from, the Royal Horticultural Society officially registers the cultivars of Dahlia. The method used here relies on flower shape. Here is an overview of the fourteen shapes according to the RHS database.
Group 1 – Single-flowered dahlias (Sin). Flower has a central disc with a single outer ring of florets (which may overlap) encircling it, and which may be rounded or pointed.
Group 2 – Anemone-flowered dahlias (Anem). The centre of the flower consists of dense elongated tubular florets, longer than the disc florets of Single dahlias, while the outer parts have one or more rings of flatter ray florets. Disc absent.
Group 3 – Collerette dahlias (Col) -Large flat florets forming a single outer ring around a central disc and which may overlap a smaller circle of florets closer to the centre, which have the appearance of a collar.
Group 4 – Waterlily dahlias (WL) – Double blooms, broad sparse curved, slightly curved or flat florets and very shallow in depth compared with other dahlias. Depth less than half the diameter of the bloom. An example are is the ‘Cameo’ variety.
Group 5 – Decorative dahlias (D) – Double blooms, ray florets broad, flat, involute no more than seventy five per cent of the longitudinal axis, slightly twisted and usually bluntly pointed. No visible central disc.
Group 6 – Ball dahlias (Ba)-Double blooms that are ball shaped or slightly flattened. Ray florets blunt or rounded at the tips, margins arranged spirally, involute for at least seventy five percent of the length of the florets. Larger than Pompons.
Group 8 – Cactus dahlias (C) -Double blooms, ray florets pointed, with majority revolute (rolled) over more than fifty percent of their longitudinal axis, and straight or incurved. Narrower than Semi cactus.
Group 9 – Semi cactus dahlias (S–c)-Double blooms, very pointed ray florets, revolute for greater than twenty five percent and less than fifty percent of their longitudinal axis. Broad at the base and straight or incurved, almost spiky in appearance.
Group 10 – Miscellaneous dahlias (Misc) – not described in any other group.
Group 11 – Fimbriated dahlias (Fim) -ray florets evenly split or notched into two or more divisions, uniformly throughout the bloom, creating a fimbriated (fringed) effect. The petals may be flat, involute, revolute, straight, incurving or twisted.
Group 12 – Single Orchid (Star) dahlias (SinO) -single outer ring of florets surround a central disc. The ray florets are either involute or revolute.
Group 13 – Double Orchid dahlias (DblO) — Double blooms with triangular centres. The ray florets are narrowly lanceolate and are either involute or revolute. The central disc is absent.
Group 14 – Peony-flowered dahlias (P) — Large flowers with three or four rows of rays that are flattened and expanded and arranged irregularly. The rays surround a golden disc similar to that of Single dahlias.
Source: Royal Horticultural society/ Wikipedia
3 more Mexican flowers that shine in our gardens
Plants from the cooler areas of South America often do try well here in our climates. It is surprising how many plants originate from here that feature heavily in our garden schemes today.
1 Ipomoea tricolor ‘Heavenly Blue’
also known as morning glory, this spectacular annual climber is an eye catching addition to the garden. The azure blue flowers which are trumpet shaped, appear newly day after day and cover the plant in colour. They are admittedly short-lived flowers in themselves, only lasting a day, but there’s no way you’ll be disappointed with so many successive blooms. It does need a sheltered and sunny site to do well and will readily climb up trellises and pergolas.
2 Passiflora mexicana
The purple passion flower is another wonderful climber that is really tropical in feel but will do well in a sheltered garden here. With the correct conditions this semi-evergreen climber will curl its tendrils around anything and the delicately scented flowers, which appear from July to September, are great for attracting bees and pollinating insects. Interestingly the name comes not from romantic passion but rather represents the mysteries of the Passion and the suffering of Christ on the cross. When you look closely at the flower there are five spots on the stamens which are some people interpret to represent the blood of the five wounds received by Christ on the cross.
3 Cosmos bipinnatus
Now here is firm favourite of mine which works in so many schemes. The Mexican Aster or Garden cosmos is a wonderful little herbaceous plant which is also native to Mexico. The flower itself is considered a half hardy annual and though it will not come back the following year, the plant does self seed itself when it has the right conditions. It’s a wonderful flower to dot in between the more fluffy spires of purple Salvia and blue Nepeta and will give a playful, bright feel to a scheme, adding that bit of Mexican sunshine to border. A bonus is that these are widely available and very reasonably priced so for a small price they really make a difference to a scheme.
Plant source @Woodies.ie