Either obtain one from the lady near the pretty petal shop near petalburg woods/rustboro city or get one using your battle points in the battle frontier.
You Can get the white herb by getting the thirty two battle points in the battletower
Gear Station
at the herb shop in lavaridge town - one of the houses
If you want a charcoal on Pokemon Emerald Talk to the old Man inside the Herb Shop in lavaridge town. He will give the charcoal. When held by a Pokemon,the Charcoal raises the power of its Fire-Type Moves.
The Power Herb is unobtainable in Pokémon: Emerald Version because it was introduced in generation four. Therefor, the only versions you can obtain it are: Pear, Diamond, Platinum, Soul Silver and Heart Gold. - MarkTheCat
In lavaridge town, next to the herb shop. Ask the kid, and he will offer to teach one of your Pokemon mimic.
In the city below mt. Chimney. it starts with an L i think. the second house on the botom to the right
go to the Herb shop in Veilstone city and talk to both of the old men there and one of them should give you the charcoal.
Herb White was born on 1948-06-15.
There's no such item as Tidal Herb.
A: the herb shop is in Eterna city
its in Lavaridge town beside the gym first house in