According to many gardening almanacs and other sources, excellent results can be obtained from "gardening by the Moon." For example, it may traditionally be conventional wisdom in a certain locale to plant seeds after the New Moon of May. There may be an actual basis for this. In some climate zones, one may expect that the time of the spring frosts may be past by early May. The New Moon may simply be a celestial signpost that conveniently signifying the proper season. We often forget today that in centuries past, the Sun and Moon were closely observed by farmers for their Biblical purposes of telling time... "for signs and for seasons, and for days and years." (Genesis 1:14).

Unfortunately, the folklore of "gardening by the Moon" is much more extensive than this and is based on silly pseudoscience. According to some folklore, if you plant during certain phases of the Moon, your garden will be less prone to weeds or insects, grubs, or other pests, and so on, and so on. There's a long tradition of gardening in this manner, going back to ancient times.

The short answer is, much of the folklore behind "planting by the Moon" is based essentially on astrology. This notion is based on a theory popular with the Greeks and Romans that the influence of the Moon somehow increases moisture depending on its phase – the New Moon is dry and the Full Moon is moist. A continuum of gradations was imagined for each day in between.

This idea derives from the pseudo-science of Aristotle which teaches "contrary qualities" e.g. hot and cold, wet and dry, etc. Take for example the four elements taught by Aristotle - earth, air, water and fire. It was believed that all matter was made up of combinations of these four elements. Each element had contrary properties of heat and moisture. "Earth" was considered cold and dry, "water" cold and wet, "air" hot and wet and "fire" hot and dry.

This notion of "contraries" also finds its way into the medical theory of the ancient physician Galen. It was thought that our bodies had four basic fluids. These were called "humors" or "tempers," i.e. sanguine, phlegmatic, choleric, and melancholic. Each of these tempers had qualities of hot or cold and dry or wet respectively. Each person's individual "temperament" was believed to result from the fluid balance of these tempers.

For centuries, this concept was the "scientific" basis for medical treatments such leech bleeding. It was thought that all disease was the result of a "distemper" or an imbalance of these bodily fluids. We still speak colloquially today of having e.g. "sanguine temperament" or a "good humor," even though the "science" behind this has been debunked for centuries.

Christians who worry about rooting out all traces of "pagan influence" should have been concerned when this ancient pseudo-scientific notion was adapted into a popular book by Tim LaHaye a number of years back, before "Left Behind" was all the rage. Apparently, only us astronomy types get scrutinized for our purity from New Age philosophy!!!

The entire system of astrology is based on the notion of contraries. All of the traditional zodiac constellations were assigned arbitrary meanings based on such contrary qualities. Modern astrologers still speak of "earth signs" and "water signs" and so forth. The Sun is considered hot and dry (for obvious reasons) so it follows that its opposite -- the Moon -- must therefore considered cold and wet. The location of the Moon in a certain phase, in a certain constellation, is alleged to increase and decrease moisture. Well the fact is, none of this is borne out by modern science. It's just a silly old superstition that persists into the 21st century.

Anyway, "gardening by the Moon" remained popular in the colonial almanacks and is still found in almanacs today. However the only proven "influences" modern science can detect from the Moon are moonlight and gravity sufficient to raise the tide. Modern meteorology does not indicate that dew and rain increase everywhere on the Earth based on the Moon phases. On any given day of the lunar month some places in the world get rain and some don't, completely irrespective of the phase of the Moon.

Nonetheless, in the face of all science, some people still swear by "planting by the Moon" and insist they get better results. If someone finds a useful practice from folklore, or just thinks it's fun, I wouldn't tell them to not do it. I would however encourage Christians to consider the sources for this notion (and any others), and seek to "prove all things, hold fast that which is good." (1 Thess 5:21)

For all who garden, we wish you a productive growing season!

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This article is from the Classical Astronomy Update, a free email newsletter for Christian homeschoolers.  Jay Ryan is also the author of "Signs & Seasons," an astronomy homeschool curriculum.  For more information, visit his web site www.ClassicalAstronomy.com.