There is no such thing as a Birthstone Dragon on DragonVale
No, emerald dragons are not breedable with any dragon. This is true of all of the birthstone dragons.
As of July 2012, there has not been a star dragon in DragonVale.
You don't breed a Kairos Dragon in DragonVale. You have to get parts to complete it.
To date, there is no grass dragon in DragonVale. You may be thinking of the plant dragon. See the related question.
The incubation time for a rainbow dragon in DragonVale is 48 hours.
The emerald dragon is one of the limited edition birthstone dragons. It was only available during May of 2012. The egg was emerald green. It took 31 hours to incubate, and another 31 hours to hatch. It was bred with a crystal dragon on the left and a lichen dragon on the right.
Brass Dragon and Fire Dragon
love dragon and panlong dragon
Sonic Dragon and Flower Dragon
Water dragon.
Fire Dragon and Lightning Dragon
Earth Dragon and Cold Dragon