The tradition of planting by the moon is a long one, practiced by many a culture for thousands of years. Pliny the Elder, Roman author, naturalist, and philosopher of the first century, even gave advice on the topic in History of Nature, Book 18. It seems obvious to take cues from nature in the garden, for instance, you may have heard a saying like, "Sow beans when the oak leaves are the size of a squirrel's ear". So, it's no surprise that utilizing the celestial cycles in the garden can give a gardener a larger connection to our environment and deeply-rooted traditions.
How it works
The moon's gravitational force pulls water upward (think of the ocean tides) and this is most powerful when the sun and moon align at the new and full moons. In theory, because there is more moisture in the top part of the soil, the new and full moons are better times to sow seeds. This tradition is further applied to the four phases of the moon that complement working with specific types of plants.
The days following the new moon are called the waxing crescent, when the moon begins to "wax", or reflect more light, building to a full moon. Think of the new moon building up to the full moon like how wax collects and builds up on a candle stick. During the first week of the waxing moon, lunar gardeners sow and/or transplant leafy annuals that you harvest above ground and produce seeds outside of a fruit. Traditionally, vegetables that are sown during the new moon are artichoke, celery, broccoli, Brussels sprouts, cauliflower, cilantro, basil and most other herbs, lettuce, spinach, kale, and other greens.
During the second week or first quarter of the waxing moon, lunar gardeners sow and/or transplant crops that produce a fruit with seeds inside, such as tomatoes, peppers, okra, melons, squash, peas, beans, and so on.
During the days following the full moon, called the waning gibbous, when the moon begins to "wane" (appear smaller) moon is thought to be good for sowing root crops, following the idea that the water in the soil is retreating to deeper depth, drawing these root crops with it, promoting healthy and strong roots. For example, sow carrots, radish, beets, and parsnips. Although onions bulbs are technically layers of leaves, because they are buried in the ground, they fall into this category, too.
Finally, that 3rd quarter or last week of the waning moon, which leads to the new moon is thought to be best for weeding, improving the soil, turning the compost, fertilizing, and harvesting other garden duties.
What we love most about lunar gardening, is the stronger connection we create to nature and the practicing of the ancient traditions that can be passed down from generation to generation--much like gardening itself.