Hi rross,
Were those other Dahlias supposed to be classic hybrids with double flowers or single flowers as well.

The parent plants of most garden cultivars are the Dahlia coccinea, which has single flowers of red (and orangish colors), native to Mexico( and Guatemala?).

There are some selections of D coccinea, slightly different colors with more or less similar growth/ habitus, rather for Dahlia geeks as their flowers are so humble.

So if your main issue is heat resistence you probably should stick to that type. If you have some garden space to spare you could try to grow some from seeds. They germinate pretty easy, you just need to choose plants with great perfomance or different flowers to collect seed from.

Plus you could asked around for heat resistent cultivars at a local Dahlia society (are there any? Or quizz some GW-folks with similar climate).

And either grow those or interplant your single Dahlias with fancy cultivars to get open pollinated hybrids ( again by collecting seeds)

Grow 50 or more per season and pick the nice ones ( hoping that there are any)
And assuming that you have gardenspace in abundance, with gardening in Australia and all...

Hope you have fun with your tough Dahlias,

Bye Lin

There are many single dahlias available for purchase. Look for ones called "Single Dahlias" or "Novalties" and buy them in different colors. I love mixing them through my flower beds, and bees LOVE them. Where as bees are having a tough time of it now, I like seeing them so happy on my single dahlias. TO me, these look like butterflies dancing in the wind among my roses and lilies and other flowers. I'm thinking of planting some with my beans and tomatoes to encourage my friends the bees.

Yes. I think this might be d. Coccinea.. I specially ordered single bedding dahlias, and the disappointing wine coloured ones I ordered are this type. In any case, I plan to divide the orange one come October, and spread it all over the garden. With any luck, the spell will stay unbroken, and I'll have a spectacular show of this weird orange next season.