Lunar planting is an ancient system known to nearly every early culture throughout the world. The moon controls ocean tides, influences the groundwater tables beneath our feet, regulates the menstrual cycles of organisms, and the movement of fluids in plants. Even continental land masses are said to rise 2 to 3 feet in elevation with the passage of the moon.

Understanding the effects, and timing planting tasks accordingly, are the basis of moon cycle planting. The Moon phase is the dominant influence in lunar planting.

The moon moves through a complete cycle every 29 days. For moon planting purposes, this cycle is divided into four quarters or phases. The term "phase" refers to the moon's shape as viewed from earth during the month. For novices, there are almanacs and calendars that list the exact times and dates of the moon phases.

Herbalists who use this lunar system and are said to produce more potent medicinal and culinary plants.

Sources:
http://www.users.on.net/~arachne/MoonPlanting.html
http://www.plantea.com/planting-moon-phases.htm