First off, if you've got a girl and you're not giving her flowers at least once a month, you're a monster. They are not that expensive. I usually just go and get a $4 bouquet every month and then she's happy. It's literally the least you can do. If you think your girlfriend wouldn't like that, you're an idiot. You're making excuses. Go get that girl flowers regularly and I swear to you, things will start to get good. If you're thinking, "things are already really good with me and my girl." Well then, get her some flowers and she'll suck the soul out of you.
DIfferent flowers have different meanings. That means both color and type. Figure out what they mean and tell your girlfriend why you got her those specific flowers. That'll impress for sure. Say goodbye to your soul.