Of course weather, air and soil temperature, and soil nutrition can also affect bloom color, but I believe the number of hours of daylight your plants receive is the *strongest factor* that contributes to color ????  change within a season.

Dahlia plants begin blooming in mid-to-late summer as we move towards autumn and days get shorter. The shorter the days, the more they shine!

In the northern hemisphere, they start blooming in our gardens in late July or early August and continue through September and October until the first fall frost sends them into dormancy. In the southern hemisphere, they usually start blooming in January and continue though summer until first frost around April or May.

Because of the way the earth tilts in relation to the sun as we move through the year here in northern hemisphere, the further north we are from the Equator (0º latitude) the quicker the days get shorter. In June, we have 16+ hours of daylight here at our farm, not counting the looong, luxurious twilight. (PNW ☀️ summers are the BEST!) By early October, however, we have around 11 hours of daylight, and by November 1 we’ll have fewer than 10 hours.

It’s interesting to consider that deep shade over your garden can contribute to a color change effect, as can streetlights and other supplementary lighting. 

In the video below, there are examples of how 6 of our favorite dahlias (Wizard of Oz, KA’s Mocha Katie, KA’s Keltie Cherry, Cafe au lait, Sandia Ruthie, and BLQ Alan) changed in color between the first week they bloomed and early October here at the farm in 2023. 

I think most of our dahlias shine their best in September and October, when days are shorter. Long considered a fall garden flower, this is no surprise to any experienced dahlia gardener. We’ve come a long way as a dahlia community getting early blooms with season extension, but I still think the best dahlias happen in early fall. Have you experienced this phenomemon?