Dahlias, along with annuals are the backbone of a nascent cutting garden. When starting out, these will be no doubt the first plants you grow. Cheap and with the quickest resulting buckets of blooms. Perennials and shrubs will take a few years to establish so a collection of dahlias will give you dramatic focal flowers from about late July through to the frosts (ha). In a season that roughly measures around 28 weeks of the year, Dahlias will flower for about 13+ weeks which is a huge chunk. Most perennials will do several weeks with annuals blooming for around 6+. You can see why dahlias are so useful and having a huge renaissance.
Currently my absolute go to for dahlia ordering is Halls of Heddon and they are showing 517 varieties to buy. Where on earth do you start? When I was first grew dahlias, I’d print off photos of flowers and move them about working out combinations between them, balancing shape and colour. I flipping love Dahlias, but they are big, all one texture of petal and frankly they are not enough; they need the supporting chorus of perennials, bulbs, annuals and foliage to really shine. Don’t fill all your available space just with dahlias, be rigorous in your edit and choose plants that will perform as stars in your arrangements and compliment what you already have growing in your space.
Whilst I am still waiting for a frost, I am choosing next years dahlia plants. The best time to order any plant is just as it is going over. If you wait until you need them, they will have sold out of all the good ones.
Nurseries show great pictures of individual flowers, and whilst a vase of single variety flowers will always look chic, mostly, dahlias look best mixed; shining best when they are very much the minority player in a display. I like mixing them with grasses, persicaria, crocosmia, salvias, coreopsis together with the foliage of physocarpus, cotinus and cornus. So how do you choose which ones that might work well in combination?
I have a rule when choosing dahlias and this is it.
GOLDEN RULE
Dahlias must fit in to either category -
Be utterly lovely and a shape or colour unfound in any other
OR
Be a real hardworking support act, a backbone and reliable shape for arrangements.
That’s it.
I’ll tell you how I choose them -
Form
Like any flower lover, I am only human and have fallen hard for the collerettes and singles. They are delicate, snap easily and short lived. Unlike most other dahlias, they need to be cut as they are just opening so that they continue to unfurl in the vase. It is tricky to get them to be just right for a bridal bouquet but when you do, they are the star. Yes, they are total divas, probably not worth the space but I absolutely love them. Lazy in the bed, they might pump the flowers out but they are made for pollinating, dropping their petals like confetti whilst your back is turned. Frustrating but utterly essential for me.
Collerettes, singles and anemones are what I call ‘singles’ with an open flower sometime a medieval ruff like centre or large puff. I group them all into one. Demanding yet irresistible. Then you have the large decorative like ‘Cafe au lait’ and ‘Babylon Bronze’. Ridiculously large flowers. Unless you are working on a huge install, they are simply out of scale and once they reach full bloom, start looking ratty round the edges. At this stage I usually throw them to the chickens for a treat but it is unusual for them to get this big. Giving an unmatched shape, and harvested just as they unfurl, the flicking out of petals from a large tight bud is perfection, adding weight and drama. Sure, they probably won’t open much further, but worth it.
I’ve used ‘cafe au lait’ here at an early stage to work with much smaller annuals to maintain balance. 
Ridiculous flower really, but then later in the season it does this. And then finally, we have the pom poms. These are hard workers. Over looked by me as dull shaped blobby blooms. But I cut these more than any other dahlia. They are long flowering and even when going over, they tuck their old petals in right at the back with true professional showmanship. My must have’s are either a solid block shade or are tonal perfection. Pom poms anchor arrangements.
Bringing together complex schemes, they can bridge across the colour wheel to calm down or hold together an arrangement.
Diminutive balls are excellent focal flowers when wired in for boutonnieres and in bud bases.
Medium sized ones are like your go-to outfit. Maybe not be a show stopper, but works for almost any occasion. That’s why we might forget them when ordering. If you only order a few dahlias, and fortunate to have a mature garden of perennials and shrubs, I’d simply go for these. They will give structure and form easily to any arrangement; in September they pair with almost any flower.
Orange pom-poms here with lilac in the background. Not exciting but bridge the different shapes here.
Now, most other shapes I just ignore. If in doubt, use the golden rule.
And then we are onto colours.
This is of course a personal one. I maintain that if you don’t like the shade, you will never cut it.
I grow some white dahlias every year for weddings but I rarely cut them. I’m not in love with green and white. There I said it. White flowers seem to suck light out of the room through the summer months. I find them cold and uninspiring. Rather, white flowers are winter flowers, spring at a push, for shady positions where pools of light are needed. Once the days lengthen and the sun rises, white flowers seem to work against themselves.
Pink is also a tricky one for me. Dahlias tend to have dark solid green leaves and in the summer and autumn months, hard to use unless erring towards much warmer raspberry tone. I mostly strip all the leaves when harvesting dahlias anyway and let the flowers do the talking (more reason to grow a lot of foliage to support them). Pink with dark green is a difficult partnership and another one I avoid.
So what colours do I like?! It’s the yellows, oranges and maroons in which I believe dahlias shine, and come autumn, they are second to none in combination when the light lowers and fades.
My Tick Sheet
Mostly, I work with my three types of dahlia shape; preferring them as a supporting act than as sole performers unless you’re only using dahlias.
I grow 5 plants in a 1.2 x 1.2m space (all our rows are 1.2m wide), so each needs to earn it’s place. ( That is, unless it’s a collarette. They can do no wrong).
I am ruthless in selection of those that I keep. We are fortunate to have sandy soil which means I can be reasonably confident in keeping the tubers in the ground this winter. I only tag those dahlias that are really brilliant, that I want to lift and divide; or, those that I will no longer give growing space to, lifting and composting.
I buy a few new ones each year to trial and supplement.
My other top tip is to take photos on your phone making an album in your notes with the names. This is a great resource because you will forget.
And finally, if you are contrary like me, your affections might waver, seeing a combination you hadn’t noticed before. I had an acid yellow dahlia that I felt had no place in the gardens back in 2018. Then a friend told me it was her absolute favourite, so I had to keep it. Then later, I saw it used with maroons and I was hooked. It’s now one of my essentials.
As I say, dahlias are not to be considered in isolation, but how they work in combination.
What are your essentials? Is there a dahlia shape or colour I have missed? Should I plant more pink? What do you think?
Gorgeous and very informative x
Love this Anna - so useful!