I used this recipe to preserve my Valentine roses and it worked great (the roses lasted almost 8 days)! Plus, I had everything on hand (no small thing here in Ulaanbaatar).
1 qt lukewarm water
2 TB fresh lemon juice (OK, I used bottled)
1 TB white sugar
1/2 tsp bleach
Immerse stems in warm water and trim with a sharp knife or flower snips diagonally. Remove all leaves that will be underwater. Place in vase with recipe and fill with warm water as needed. Replace with fresh recipe every other day or so.