Bieber BUYS OUT Flower Shop for Selena Gomez

Justin Bieber scored major points with his GF Selena Gomez last week -- when the 16-year-old phoned in a GARGANTUAN flower order ... and it wasn't even Valentine's Day!!!!

Sources close to Bieber tell us Justin called up a local florist on Wednesday hoping to "fill Selena's house with flowers" ... just because he felt like it.

We're told the florist needed EVERY SINGLE FLOWER in the shop to complete the order ... and had to use "multiple trucks" to pull off the love stunt.

One source close to  the couple tells us Selena LOVED the surprise.

Source: tmz.com