Dahlias have a reputation for being fussy in heat, and there’s some truth to it — but “difficult in hot climates” is different from “impossible,” and a few adjustments make a real difference in Australian summers.
Give them afternoon shade
Full sun is the standard advice, but in genuinely hot zones, dahlias appreciate protection from the harshest afternoon sun — morning sun with some afternoon shade (from a taller plant, a fence, or shade cloth) keeps them producing without scorching.
Mulch heavily
Dahlia tubers sit close to the surface and dry out quickly in hot soil. A thick mulch layer keeps root temperature down and moisture more consistent — similarly to how mulch helps prevent the tomato splitting issue covered in our tomato splitting guide.
Water deeply, not frequently
Deep, infrequent watering encourages roots to grow down rather than staying shallow and heat-stressed. A quick daily sprinkle does more harm than good in genuine summer heat.
Consider lifting tubers in the harshest zones
In the hottest inland and northern parts of the country, some growers lift and store dahlia tubers over the peak of summer, replanting once the worst heat has passed, rather than fighting the plant through months of extreme conditions.
Pick varieties bred for warmth
Not all dahlia varieties handle heat equally — smaller-flowered, more compact varieties tend to cope better than giant dinner-plate types, which can wilt and struggle in extended hot spells.
Dahlias are worth the extra care — see our easiest cut flowers guide for how they compare to lower-maintenance options if you want to start simpler first.