If you are strapped for Gems, PvZ: Heroes has added a way for you to gather some by watching advertisements. It appears you can watch three ads in total which will net you ten gems for each ad watched (30 in total). Once the third ad is watched it will lock your ability to view anymore for an undetermined amount of time (I’ll update this with the exact refresh time). Most guesses are around a day, but I haven’t been able to confirm it yet. To take advantage of this, check out the small gem icon on the top right side of your screen!