Collecting all nine flowers is the objective of the "Nine Realms in Bloom" favor. This favor appears in your journal when you find the first of the flowers. The flowers are located in places you will reach in the later stages of the game and some of them you will be able to collect only after completing the main storyline of the game. Once you collect all nine flowers, you will unlock "The Florist" trophy.
You can admire the flowers you collected in one of the rooms in Sindi's house.
Mirkweed (Midgard)
A rare, hardy flower that somehow managed to survive in Midgard despite Fimbulwinter. It has earned my respect.
Sparkthorn (Svartalfheim)To get here you need the Draupnir Spear, which you will acquire later in the game's main storyline.
More of a weed than a flower, it grows in Svartalfheim and is the rare flower that can defend itself.
Dawnbloom (Alfheim)
A colourful flower found in Alfheim. According to Freya, they always point toward the Light of Alfheim even once plucked from the earth. I suppose it is not unlike our compass, capable of guiding us home when we are ready.
Ironbell (Jotunheim)
A slow-blooming flower from Jötunheim. I know this one. Faye used to plant them many years ago, though I incorrectly assumed it native to Midgard.
Starblush (Vanaheim)You will be able to get here only after the water in the rivers is restored, so you must first complete the favor "Return of the River".
Found in Vanaheim, and said to turn crimson in the presence of a shooting star.
Ashpetal (Muspelheim)
A burnt flower from Muspelheim. It somehow makes a home amid that ash and fire.
Dreamshade (Niflheim / Asgard)You will find this flower in one of the cells on the lowest level of the prison.
Freya spoke of keeping this flower in her room during her time in Asgard. She said it is perhaps one of her few good memories of that time.
Frostfinger (Niflheim)
Not much can survive in Niflheim. To grow alone in such a place must be a lonely existence.
Soulblossom (Helheim)You will reach this place after finally defeating Garm. In order to get to the other side where the flower is, you need to use the Draupnir Spear.
It is hard to believe anything can grow in Helheim, the realm of the dead, but this flower has found a way.