Twenty of the best new dahlias

Dahlias on trial, in the new RHS Wisley Trials Field
Dahlias are one of the first plants on trial in the new Trials Field at RHS Garden Wisley, opened in summer 2021. The trial puts to test many recently introduced varieties that are available in the UK, and the best ones will be given the Award of Garden Merit. Here are my top 20, A-Z, but I didn’t think too hard about it and I don’t have strict criteria. There are so many exciting varieties there, all sizes, and a good range in being trialed in pots too. The trial will continue next year, looking best in late summer through to autumn, so come and have a look for yourself.
Dahlia ‘Aggie White’
1.2 to 1.4m tall, with flowers 25-38cm wide. Introduced in 2017 by Christopher White from Ireland. A sport of ‘Bryn Terfel’.
Dahlia ‘American Dawn’
This was one of my favourite from my allotment in 2020, so I grew it again on my student plot at Wisley. Garden visitors loved it. The purple undersides of the petals make a great effect as you view the flowers from different angles. 0.8-1m tall, flowers 10-15cm wide.
Dahlia ‘Askwith Edna’
1.5m tall, flowers 15-22cm wide. Introduced in 2015, by the late Ernie Cawkwell, of Askwith Nurseries in Sunderland.
Dahlia ‘Brown Sugar’
A floriferous pompom dahlia, 0.8-1.2m tall, flowers 8-10cm diameter.

Just after taking these photos in mid-September, I spent a week working with Jimi Blake at his magnificent Hunting Book Gardens near Dublin. Jimi is a complete maverick and master plantsman, and uses dahlias to perfection in his eccentric and exuberant plantings. He was desperate to come and see the trial, but by the time he visited a month or two later, a frost had hit them just the day before. I promised I’d send him my photos, so these are for you, Jimi!

Dahlia ‘Crème de Cassis’
A nice stocky ‘bedding’ dahlia that does well in pots. ‘Crème de Cognac’ is also in the trial, caramel petals with brick-red undersides. Both are 0.6m tall with flowers 10-13cm across.
Dahlia ‘Encore’
One of my absolute favourites. Fimbriated petals, 0.9m tall, flowers about 20-23cm across. A sport from the variety ‘Show n’ Tell’, introduced in 2002 by Swan Island Dahlias in Oregon.
Dahlia ‘Hadrian’s Sunset’
A chance seedling from Halls of Heddon Dahlias, 0.7-1m tall, flowers 8-10cm wide. Very dark foliage.
Dahlia ‘Hapet Blue Sea’
A highly floriferous waterlily dahlia. 1.2m tall, flowers 9-11cm across.

I went big on dahlias a on my allotment in 2020, and wrote about it here. Quite a few of those varieties are in the trial at Wisley. The soil on my allotment is fairly heavy, and it’s high on a Pennine hillside that’s very wet and cold all winter, so I decided to dig them all up for storage over winter as they are technically tender. I dug them up, cleaned them off and left them in my allotment greenhouse to dry off before they’d be packed away somewhere frost-free.

Dahlia ‘Hapet Champagne’
Another beauty with fimbriated petals. 1.5m in height, flowers 15-20cm wide. Raised by Peter Haslhofer in Austria, introduced in 2014.
Dahlia ‘Hillcest Firecrest’
Vibrant bi-colour from Les Jackson in Carlisle, introduced in 2016. Deeper more vivid orange colouration seems to be stimulated by hot sunny weather, while overcast conditions make for more yellow flowers. 1-1.2m tall, flowers 10-17cm across.
Dahlia ‘Josie’
Named after Sarah Raven’s head gardener, Josie Lewis. Similar to ‘Totally Tangerine’ but quite a bit brighter. 0.9m tall, flowers 7-9cm wide, loved by pollinators!
Dahlia ‘Josudi Hercules’
A miniature cactus dahlia. One of the Josidi series, raised by Peter Greenway in Cornwall. Introduced in 2016, this variety is a 2013 seedling from 2 of his other raisings, Josudi Pegasus and Josudi Neptune. 1.2m tall, flowers 10-15cm across.

That night we had a really extreme unexpected cold snap, and all of the tubers we hit by frost. Over the coming weeks, the consequences of this unfurled as they all rotted off despite my desperate attempts to save the 100 or so plants by drying them out under a fan indoors, and dusting with sulphur. Every single one rotted off. But what I did learn that year was how easy they are to root from tip cutting on a heat mat in spring, and also how easily the tubers can be divided or literally cut up, once the shoots start to show. You just need a shoot with a bit of tuber and some roots. There’s some photos of this at the end of my blog from last year.

Dahlia ‘Jowey Martina’
A gentle and floriferous pastel yellow pom-pom, 1-1.1m tall, flowers 6-8cm wide.
Dahlia ‘Mister Frans’
A very classy waterlily-type dahlia. 0.9m tall, flowers 8-10cm wide.
Dahlia ‘Penhill Dark Monarch’
A colourful form of the ‘Café au Lait’-style and size of dahlia. 0.7-1m tall, with flowers a whopping 20-25cm wide.
Dahlia ‘Polventon Kristobel’
Introduced in 2016 by Cyril Watkins from Cornwall, 1.2m tall with flowers 9-11cm wide.

From now on, like many people across the UK, I will not lift my dahlias for winter. The inevitable disturbance and damage opens them up to rot, it’s a mighty faff, and I don’t have room to store them suitably anyway.  Instead, they get a bucket of chunky compost mulch dumped on top in late autumn, to keep the frost from penetrating down into the soil. Provided the drainage is reasonable, they should be fine. And it saves all the faff of having to plant them out in spring too.

Dahlia ‘Sincerity’
0.8m tall, flowers 8-10cm across.
Dahlia ‘Stadt Spremberg’
From German dahlia breeder Steffen Koschker, introduced 2005, named after the City of Spremberg. 1.5m tall, flowers 9-12cm across. This is the only Dahlia in the list that isn’t in the Wisley trial, but you can see it just outside the trials field on the mixed borders. Not easy to get hold of in the UK, so happy hunting and let me know if you find it for sale!
Dahlia ‘Verrone’s Obsidian’
I grew this star-flowered variety on my allotment in 2020, along with a few other single-flowered dahlias. They are great for pollinators due to their open centre, but I find they don’t last long in the vase and need mire regular deadheading. 0.9m tall, flowers 8-10cm wide.
Dahlia ‘Zundert Mystery Fox’
Strong grower with long, strong stems typical with the ‘Fox’ series. Streaks of violet through the petals make the colour look super-saturated. 0.9-1.1m, flowers 10cm wide.

All photos by Owen Hayman, September 2021.