I first heard of this some years ago, and when I found myself browsing a bookshop in London one evening in 2006, I found this book.
The basic principle is that growth of plants is governed by the moon, or more accurately by the sidereal zodiac (not the same as the zodiac used by astrologers). There is a huge amount of detail to this, but put simply there are days on which it is best to sow seed, or plant out the four types of plants:
- root - e.g. beetroot, onion, potato, carrot
- leaf - e.g. herbs, lettuce, cabbage, spinach
- flowers - e.g. broccoli, cauliflower, flowering plants
- fruit-seed - e.g. apple, beans, cucumber, peas, pumpkin
You can go to huge lengths in this planting regime, but I don't have patience for that. The only other rule I tend to abide by wherever possible is to plant in a waxing moon as they do better that way. The downside is that if you miss a window to plant something, you have a 10 day wait until it comes round again, but I have learned not to worry about that.
The first year I tried this convinced me the effect was real. The onions were bigger, the peas and beans better and so on. So when I look at other vegetable plots and see their plants smaller and less healthy than mine, I know the reason why. I happily share this with gardeners who ask, but they just think I'm mad...
If you fancy trying this, I suggest you start with a book to get your head round it - after that you can get calendars separately or online for each new year. The book above is by Nick Kollerstrom.
UPDATE: I should have said that this is not foolproof - the heavy rain in the last week has killed off some of my seedlings, for example.