For others who have the Crystal Unicorn and are seeking your FIRST Emerald Dragon, look for the Nature family from which you are missing the most hybrids, and pair your Unicorn with one of them.
If your Unicorn breeds with a Nature hybrid instead of a pure Nature (like Panda), you will bypass the blocker. Okay, the fails will be longer than even a 1-hour Panda, but at least you may find a missing breed among them.
The Nature-Fire family will offer the shortest set of fails, but if the only Nature hybrid you're missing is the Emerald itself (lucky you!), the 1-hour Panda breeding -- unfair as it is -- will be a relatively small obstacle.
(Believe it or not, the only Nature-Fire I've EVER been able to breed is Fairy Ferret! So if I were trying for my first Emerald, Unicorn-Ferret would definitely be my choice for the Garden.)