I followed the instructions in the Swan Island catalog, which says to lower the freshly cut flowers into HOT water at 160-180 degrees Fahrenheit, and leave them there to cool for an hour.

So I've repeatedly tried this, but usually the hot water causes the stem to turn very dark, very quickly, and the bottom of the flowers even turned black once or twice, even though I slid a cardboard piece between the flower and the hot water.

Also, the flowers are only lasting 2-3 days til they are looking bad. A few years ago when I grew my first dahlias, which were a 4-5" wide and very thick decorative variety, they would routinely last a week or so after I only placed them into room temp water.

A while ago I read something about adding some household chemicals to the vase to make them last longer....

So, what are your ideas for making dahlia flowers last longer?