Seize the Da(y)hlia

Dahlia!

What can be said about these old-fashioned favourites, other than - fantastic. Long the prized plant of old-school country fair and allotment growers, dahlia are back in fashion. Mainly, because when it comes to colour, shapes and sizes – as well as value for money – dahlia just can’t be beaten.

A Brief Summary

As bright and colourful as the colours found in their native Mexico, with their dramatic spreads of colour in summer and autumn, there’s one there for everyone. The actual appearance of the plant is pretty much the same among the species, with most being small to large bushes.

Where to start, considering there are around 40 species, and hundreds, if not thousands, of cultivars and hybrids. In the past century, nearly 50,000 named varieties have been listed in various registers and classification lists!

If you’re in a garden centre and you see bedding dahlia in pots, these are ones that have been grown from seed and have yet to develop their tubers, whereas the bulbs you’re going to be planting are obviously – tuberous dahlia. That’s the essential difference between the two. With the others being that the bedding varieties are generally accepted as annuals, and don’t get quite as tall, maturing at around 40 – 60cm, as they've grown to be potted up for the nursery.

When it comes to your bulbs, firstly, they’ll start to flower from around Christmas into the first couple of weeks of January, so if they haven’t come up yet, don’t panic. It takes about eight weeks from planting (which you should do around October/November) to flowering. 

It does help to group your dahlia in an organised system, as there are six dahlia varieties along with seven form classes. Yes, we know, we’re throwing lots of figures at you, but it does get easier!

How to Distinguish Between Them

When you start trying to tell the difference between dahlia, the similarities become a tad vaguer. 

They get divided into flower form classes, which indicates the shape of the flower and the character of the petals – if you’re going into more depth. The easiest way of separating the varieties is just by eyeballing the size of the bloom. Considering they range in size from 4 – 25cm in width, you’ll need to know what you’re getting to ensure you put the right thing in the right place! They’re fairly forgiving plants, and bloom best in full sun, planted in fertile, well-draining soil.

Dahlia Decorative

Decorative types are the largest of the genus and offer a huge array of colours – pretty much everything except true blue or black. They may be formal or informal and have flowers thick with petals that are usually flat – but often have tightly rolled petals resembling a honeycomb. They’re generally reminiscent of pompoms and balls (and of course the balls are exactly what they say – ball-shaped, or sometimes a slightly flattened sphere and do get slightly larger than the pompoms). These are usually the smallest of the blooms, at around 4 – 10cm across, but what they lack in size, they make up for in cranking out loads of flowers all season. 

There are singles and doubles, and Mignon dahlias which are similar to the singles - and are sometimes even categorised together. The main differences are mignon dahlias tend to be under 5cm in diameter and feature petals with round tips. 

Dahlia Border

Moving up slightly in size, you’ll find the border dahlias, which are fairly compact and reach around 30 – 50cm tall, so never need staking – perfect for pots, planters, and lining a walkway. They may be small in stature, but they have full-sized flowers of 8 – 12cm diameter. 

Dahlia Dinnerplate

The largest pick of the bunch are the dinnerplates, with really BIG blooms. The plant can grow to around 1,5m tall and has flowers that can measure as much as 25cm across. So give these guys some space at the back of a flowerbed, against a walk for support or use something to stake them so they don’t get droopy heads. Allow them to stand loud and proud, showing off their glorious faces to their best. 

Dahlia Cactus

Then there are the really showy, dramatically shaped cactus types, which have a starburst effect. Double-flowering, these spiky looking blooms are as soft as they come, as they do have slender stems so you may want to stake them to help support their fluffy heads. 

The rest

Moving on, we find a broad class of singles, semi-doubles, collarettes and anemones, each of which has a star-like appearance with flat petals surrounding a distinctive disc. The latter two, which rarely get taller than 75cm tall, often display two or more colours and offer lots of interesting textures. The difference between these two prolific bloomers is that the anemone has a pincushion of tubular florets at the centre, surrounded by several rows of more traditional petals, and can reach 60 – 90cm in height, while the collarette has two different petal lengths, with an inner row of short, frilly petals surrounded by standard petals. Both of them are great for containers and smaller gardens. 

Then taking their names from flowers they mildly resemble, there is the peony variety, which has irregularly formed petals, giving this unique bloom a fluffy look. They get to around 60 – 90cm tall. The orchid dahlia, which actually doesn’t look anything like orchids, by the way, is single flowering with the doubles having two rows of petals that hide the centre of the flower. Then there are those with a flat, closed centre and broad rows of rounded petals swirling around it in the water lily family. These ones DO resemble their namesake! They only get to about 0,5m tall but produce large blossoms that measure up to around 12 -14cm across. Let us not forget the Stellar – although, in our minds, they’re all-stars in their own rights. 

We hope this has given you a bit of help when it comes to deciding what you want! 

Read more about Dahlias: The Darlings of Your Summer Garden here and our Dahlia Do's and Don'ts here.