I am terrible at keeping plants and flowers alive, so my fiance and I finally just bought some very realistic plastic ferns and flowers for our front porch. I could care less if they're fake. They look a lot nicer than the dead, brown stuff that was previously hanging and sitting there.
It's impossible dear. We can't stop them from dying. But I can suggest you that use artificial flowers. They will live forever but they will don't have a fragrance. See here silk flowers http://www.justartifacts.net/silkflowers.html