Tip: Put cut dahlias in a dark, cool place to rest several hours or overnight once you receive them. If you want to give them the best chance to last, recut stems (an inch or so) underwater while arranging them in your vase. For fat, hollow stems you can go the extra mile and pierce the stem several times underwater to allow any accumulated air to escape (better water absorption- no air blocking water uptake.) Keep dahlias out of hot sunlight: cooler is kinder.