The moon is known to directly affect the tides of the ocean. Is it so far-fetched to suggest the moon also dictates the best time to plant root crops and above ground crops? Check out this website for an interesting article on just that: http://earthyfamily.com/A-planting.htm
Increasing Light -- New moon to full moon
Accordingly, during this period one might sow seed for plants that grow above ground ie. peas, tomatoes, lettuce. ( See a guide specific to this topic such as Ed Hume's Planting Guide or The Farmer's Almanac for specifics.) The waning phases are those when the moon goes from full moon to new moon. During the 3rd and 4th quarters, it is suggested this is a good time to prune plants. The water table diminishes and less sap will flow from cut ends. This is a favorable time for planting, transplanting and harvesting root vegetables. The most dormant period is during the 4th quarter and is ideal for weeding.
Decreasing Light -- Full moon to dark of the moon
During this time it is suggested to be ideal for planting of bulbs; root crops such as beets, potatoes, carrots; perennials, biennials and bulbs. It is also a good time to prune shrubs. (Keep in mind the rule of thumb - prune as necessary once the shrubs have finished flowering.)
Again, I recommend referring to a source specific to this topic such as Ed Hume's Planting Guide or The Farmer's Almanac. I have not experimented with this method so I cannot guarantee results but it is an interesting approach. Afterall, farmers have been doing it for years. That must say something as to its validity.