I know they grow lilac far up in northern Sweden. So that would be an option for outdoors. Here in the south they flower in May, but up north I have seen them flowering in August.

I am not totally familiar with Colorado climate. Do you get a lot of snow? Many species does work very well despite cold winters if they are burried in snow. The conditions under a deep layer of snow is very favorable.

Anyway, the most common advice given to beginners is to start with locally hardy materials. Look arround you in gardens and forrests. Are there any flowering trees growing there? Those are your best option.

Thanks, Tropfrog. Yes, it snows here, but the weather is a little weird. It will snow like crazy, but then melt away in two or three days. I appreciate the advice. It's a great idea to check with local sources and explore the actual flora.

Sounds like my climate. If you don’t get prolonged periods below freezing all species mentioned in this thread except pomongranade and desert rose will do fine outdoors.