Dahlia Flower How Long Do They Last. They are slow to get going and often dont flower until the end of July or even early August. The more you cut a dahlia plant the more it will bloom.
However the most important word in that first sentence was can. A heavy frost will kill the plant and leave you with a decision on your next step. Another techinque pinching dahlias applies the reverse.
Depending on where you live that could mean that you can have dahlias in bloom for three four or even five months.
If they last longer they are pleasantly surprised. Oct 13 2015 Some of their success is part of the nature of dahlias but the reason they are still blooming and blooming better than ever is because I have been good about deadheading them. If you keep on top the deadheading dahlias will bloom right up until frost. At the top or lay it on its side and back-fill the hole gently covering the tuber completely with a few inches of soil.