Plant gathering
From DwarfFortressWiki
Plant gathering allows you to gather plants to add to your food stores. The skill associated with plant gathering is Herbalism.
Plant gathering can sometimes make all the difference between surviving and starving. However, the plants you gather may require some processing, and in a few cases (such as hide root), cannot be made into any food item.
To gather plants, at least one of your dwarves must have the "plant gathering" job turned on. Then find an area with a lot of shrubs (Shown by " symbols.), then press d for 'designate', and then press p for 'plants'. Move the cursor to one corner of the area you want to harvest, and hit enter. Now move diagonally to the far corner of the area, and hit enter again. This will mark all harvestable shrubs in that area for picking.
Your dwarf should then start going out to pick those plants.
Plant Gathering is also essential for obtaining seeds if you plan to do outdoor farming. The plants gathered must first be brewed, milled or eaten to obtain the seed.

