Waterleaf is a type of Herb which appears as a very small, aqua-colored sprout. It grows on Sand and Pearlsand blocks in any type of Desert biome and can be cut with virtually any weapon or tool. It can also be planted in Clay Pots using Waterleaf Seeds. The Waterleaf takes the longest to bloom out of all the herbs.
Waterleaf is a finicky plant, and will only bloom when it's raining or snowing. When fully grown and it's raining or snowing, it will bloom and its appearance will change, becoming larger and speckled with aqua leaves. A blooming Waterleaf will also emit little globes of water. Note that it does not need to be raining or snowing directly on the plant in order for it to bloom, rain or snow just needs to be falling.
The Mobile version of Terraria still requires that Waterleaf plants are at least partially submerged in water before they bloom and drop seeds. It doesn't matter if it's raining or not; if the plants are submerged, they will bloom and yield seeds when harvested.
In all versions, harvesting Waterleaf while it's blooming will drop 1-3 Waterleaf Seeds.
Waterleaf can grow on sand underground if it's placed or converted by the transition to Hardmode; this includes Ebonsand and Pearlsand.
One should despawn all minions before harvesting waterleaf, as minions with piercing attacks (and under the right circumstances, ones without them) will destroy your plants, and will not drop the item/seeds. If one does not have any extra seeds, you will have to harvest more from a desert.