You can buy Verdium for crystals in top left corner of the home screen.
This makes very little sense, but if you are very eager to play more and have crystals to spare, of course you might select to do this.
Other means to earn more Verdium:
- Sometimes blue containers contain Verdium
- Buy it from broshop
- Of course the daily quests with 2 times 50 units of Verdium (unless you already are above 300 units)