Dahlias respond to many different variables. If it was very hot in July where u live that could have caused the dahlias to stall out. It's not a simple formula of start six weeks early get six weeks more flowering. Some ppl say early started pot dahlias are more prone to stalling out like this but prob depends on weather, soil, varieties planted and myriad of other factors. Indoor pot planted dahlias are def more prone to rot so theres that strike against it.

Dahlias are from Mexico yes but they are from a mountainous climate with cool nights. Sustained high heat can retard flowering and or foliage growth. Lots of growers in the NE--heat wave, severe drought--for ex didn't get any blooms at all until September. So your experience seems typical.

I was super late planting many of mine bc of terrible covid timing and lingering after effects and very late planted dahlias started blooming around the same time as tubers set out months previous.

"It's not a simple formula of start six weeks early get six weeks more flowering. "

Thanks for the explanation. I was under the impression an early start indoors would yield a bloom period starting in early July. Instead they reached peak bloom at the beginning of September and are still going strong. We have had a few nights down to the mid 30s, with highs anywhere from the id 50s to a few days of the mid 70s. So far no frost yet, and the blooms continue. July was very hot and dry here- based on the information you provided the weather caused them to stall. I prefer hot summer weather, so a lack of dahlia blooms is OK with me if hot weather is the reason.

Thanks again for the information.

I was expecting them to bloom in July. Is that an unrealistic expectation?

@kc270 I only store a couple of dahlias each year and I start mine early i.e. the first week of March and they are in bloom indoors in less than 2 months i.e. before the end of April. And so once I put them outdoors they are always in flower.

(see my last post here: https://www.houzz.com/discussions/6359323/i-am-always-in-awe-when-i-see-our-dahlias-poke-through)

@rouge21_gw Thanks for sharing your experience. I am amazed that you already have blooms

In 2021, the dahlias I started indoors got tall before it was warm enough for them to go in the ground. In 2022, I pinched them when they got around 12" tall, but not much blooming until the end of the growing season. In 2023 they are still in the basement. I am going to start a few in pots this week to see how they bloom compared to those that I put straight into the ground at the end of May.

I am amazed that you already have blooms

Thanks @kc270.

(Actually, right now, the flowers of one of these dahlias (4 flowers in total) look better than it did outside all last season!)