It's difficult to know when moon gardening originated, and modern horticulturalists have yet to fully endorse the practice. However, Pliny the Elder discussed the method back in the first century. "Planting by the signs," as many old-timers call it, takes into account both the signs of the zodiac and the phases of the moon. Needless to say, charting all of these conditions can get complicated. In fact, many believers focus solely on lunar gardening, which focuses on the overall tasks appointed to each week (moon phase), rather than the best days within that week (zodiac signs) to perform them.
A lunar calendar is a convenient way to keep track of what phase a proposed gardening task falls under. Each quarter lasts seven days. The first quarter represents the week following the new moon, in which the crescent moon "waxes," or seems to get bigger each night. The moon in the second phase appears as a half-moon. The full moon starts at the beginning of the third quarter, and begins to "wane," or get smaller. The fourth-quarter phase begins seven days after the full moon, and wanes back to a crescent shape.
Plants whose useful parts grow above the earth should go into the ground while the moon is waxing, and those whose useful parts grow below the ground need planting during the waning phase, especially the third quarter.
During this earliest moon phase, graft trees and plant annual flowers. Vegetables believed to flourish when planted in the first quarter are those which set their seeds on the outside, including corn, lettuce and spinach.
This is the time to plant vegetables and fruits whose seeds are protected by a pod or skin, including tomatoes, squash, beans, watermelon, pumpkins and peppers. Get perennial flowers in the ground sometime between the second and fourth quarters.
Straddling the second and third quarters, the day of the full moon is sometimes saved for special gardening tasks, including planting medicinal herbs. Some people believe that harvesting these herbs just as the full moon begins to rise increases the plants' healing powers, notes Ellen Dugan, the author of "Garden Witchery." The Farmer's Almanac reports that many believe horseradish harvested at the full moon will have the most intense flavor. The website Gardening by the Moon notes that studies conducted by Frank Brown at Northwestern University concluded that more moisture is in the soil during the full moon. Although many plants need daily or weekly watering during dry spells, the full moon may be the best time to water stressed plants.
The third quarter is the best one for pruning, according to Gardening by the Moon. Plant perennial flowers, shrubs, bulbs and trees in the third quarter. Root crops which traditionally go into the ground during this phase include radishes, onions, turnips, potatoes and carrots. Harvest fruits and vegetables just after the full moon.
Little planting should go on during the period that begins seven days after the full moon. Use this time for fertilizing, tilling, cultivating and turning over the soil. Destroy weeds or dead trees during this period. It's also considered best to do your preserving in the final quarter, so plan for marathon pickling and jam making while the moon wanes.