DMM Devs are very generous. Per month they have this sort of event which gives you alot of free stuff as a log-in bonus including at the very least, 10+ Flower Gems. They also give alot of Flower Gems if the servers experience any problems such as lag or maintenance issues and give around 10 - 150 gems during these times as their way of saying sorry.
As long as you're not spending your flower gems on other stuff you should be getting 50 gems every 2 weeks. That's a roll for every event.