Currently, there are six flax fields located in Gielinor.
The first flax field is an area next to the beehives where the player can pick flax. There is also a building with a spinning wheel to the west where players can spin the flax into bowstrings. It is just south of Seers' Village and west of Catherby. It is a popular area with players picking flax as an early temporary moneymaker as flax can sell for about 35 coins each. After completing the Seers' Village Tasks Geoffrey will collect flax for you when wearing a Seers' headband.
There is also a second flax field in the Elven town, Lletya. It contains less flax than the location at Seers' Village, but this flax field lies closest to a bank. Players need to have begun the Mourning's End Part I quest to gain access to Lletya.
A third flax field that can be found in the south-east region of the Tree Gnome Stronghold, it contains lots of flax spread throughout the area. Spinning wheels can be found nearby. A bank can also be found north-west of the area.
Some flax herbs can be found on Lunar Island, it contains a low amount of flax, and it is spread out over the south part of the island, on the way from the city to the Astral Altar.
A fifth flax field exists in Taverley. It's small and contains a low amount of flax which makes it quite impractical.
A sixth flax field can be found in the Cadarn Clan section of Prifddinas, just north of the max guild. It is situated directly west of a spinning wheel, making it a good place to spin bowstrings.