Growing Dahlias in High Heat

Well growing Dahlias in my zone 7a/7b is a bit of a challenge. I live in a high desert region, and it has been having record breaking over 100-degree weather.  I grew some of my dahlias from seed from Floret -Bee's Choice Mix.  I have been growing in a plastic barrel container.  It isn't ideal and I have been watering a lot, but the plants have produced some blooms. I think they are a bit heat stressed. I am going to move the container to a shadier afternoon location because I am not getting the production.  I have heard that shade cloth can help to make plants less stressed.

My Walmart had on clearance a lot of their plants. I got 3 dahlias for 4 dollars apiece. I can't buy a tuber for that price.  They are a little shaggy, but I think I can keep them going for a bit longer.

Triple Wren Farm and Heat Can Affect Dahlia Color