Until Sunday, January 25th, 2015. all plants will give double xp, rewards and seeds at elder!
When your harvest your plants at elder during the member benefit event, you get double gardening xp as well as double rewards which also includes double seeds! I was able to harvest my Evil Magma Peas, Deadly Helephants, Couch Potatoes and get double xp as well as rewards and seeds from them. You can easily double your gardens this way. And because of the double xp I received, I also was able to level up because of this. It's an amazing bonus that you should take advantage of right away! You only have a limited time to do it, so hurry up before the event is over.