From       (1900 words 1 graphic)       Home       Fast-Find Index

Plantinq by the Moon
Explaining a persistent myth

By Jackie French

This article originally appeared as "Why Moon Planting Works" in the Skeptic 25(4), 20-21, Summer 2005. The description of Moon planting systems has been enlarged. Jackie French is the author of many gardening books, writes various gardening columns, and for ten years was a presenter on a popular Australian TV gardening show. Her article is one of the few on lunar gardening written by a professional gardening expert.

About 15 years ago I decided to see if Moon planting worked. For those unfamiliar with the subject, Moon planting assumes that Moon phase and zodiacal Moon sign influences the way plants grow. Some phases and signs are said to promote growth, others are said to retard growth, and it depends on whether the target crop is leaf, fruit, or root. Yes, it sounds like nonsense, but many gardeners (especially the my-organic-tomatoes-are-bigger-than-your-organic-tomatoes sort) swear that they owe it all to Moon planting. So it seemed worth investigating.

Systems of Moon planting
The idea that the Moon affects plant growth is an old one. It can be found in the folklore of ancient societies ranging from the Celts in Britain to the Maoris in New Zealand. Roman historian Pliny the Elder in his History of Nature, Book 18, gives much advice on planting by the Moon. Today it is still a rural tradition, and in most countries you can buy Moon gardening guides. Less well known is the existence of three different Moon planting systems, each disagreeing with the other two.

Moon gardening guides

Left to right, Moon planting guides from USA, France, and UK, favouring Systems 2, 1 and 3 respectively.

System 1 is based on Moon phase. Plant growth is supposed to follow the increase or decrease in the Moon's light. So you plant crops or pick grapes during the waxing (increasing) phase, and harvest crops or cut timber during the waning phase. A refinement says you plant crops like peas whose yield is above ground during the waxing phase, and crops like carrots whose yield is below ground during the waning phase. Note how the refinement contradicts the original view. Other contradictory views exist. Thus one says you should sow seeds just before New Moon so the seeds will germinate and start growing in the waxing phase, while another more widespread view says you should sow seeds just before Full Moon. They can't both be right.

System 2 is based on zodiacal signs and says the best time to plant is when the Moon is in a Water sign (Cancer, Scorpio, Pisces). Earth signs may be acceptable for root crops, but Fire signs are the worst time and Air signs are neutral. Since a Water sign occurs every 7 days and lasts for 2 days, you need to keep your eye on the clock.

System 3 is similar to System 2 except sidereal Moon signs are the important ones, not the tropical Moon signs featured in System 2. The difference is nearly one sign and is slowly increasing, so when the Moon is in tropical Water signs it is largely in sidereal Air signs. Nevertheless the same superiority of Water signs is claimed for each system and each has its followers. For example System 2 is favoured by the Moon Sign Book (published annually in the USA since 1906), which organises annual contests for the best fruit or vegetable garden grown according to its guidance, while System 3 is favoured by the bio-dynamic movement founded by Rudolf Steiner (1861-1925).

Lest you dismiss these conflicting Moon claims as sheer lunacy, be aware that there is good evidence supported by a large literature that moonlight does affect plants, both directly eg via stomatal activity and indirectly eg via insect activity. But such effects are very different from those claimed for Moon planting. There is of course the old argument that the Moon affects the tides, so why not people (80% water) and plant sap? The argument is invalid because the Moon causes tides only in very large unbounded bodies of water like the world's oceans. Bounded bodies of water such as land-locked lakes, unless very large like the Great Lakes, are negligibly affected. So forget tidal effects in humans and plants unless they are of planetary dimensions.

Perhaps the most comprehensive review of biological Moon effects is that by the biologists Klaus-Peter Endres and Wolfgang Schad in their book Biologie des Mondes: Mondperiodik und Lebensrhythmen (Leipzig 1997). They found that some plants and animals showed no connection with moon phases, while others did show a small connection in their growth or reproductive behavior but not consistently -- for some it was only at full moon, others only at new moon, and still others only at waxing or waning quarter moon. So even this review hardly helps moon planting.

Testing Moon planting
Testing Moon planting is not simple. It's easy to test a new fertiliser for example -- you use four or six plots as identical as you can make them, each planted with seeds of the same bean variety at the same time but grown with different fertilisers. Watch how long it takes for the first flowers and the first beans to appear. Then weigh the crop, make a note of pest numbers, diseased leaves, how many days the plants fruit for, and so on. Finally compare results.

But this wouldn't work for Moon planting. Regardless of which system you follow, the whole essence of Moon planting is that, depending on the crop, there are only a few ideal days each month in which to plant. But we can't just plant beans on those Moon days and on some other days for comparison, because any beans planted before the Moon days would have longer to grow, and any planted afterwards would have less.

Finally I dug six long rows and planted two bean seeds in each row every day over a three-month period. If the Moon planting theory worked then the bean seeds planted on the optimum days should do better than the ones planted either side. They didn't. Of the seeds planted in the first month, those planted after the Moon-planted seeds flowered earlier and were more productive. In the second month the effect was similar but not as marked. In the third month the beans flowered in an almost perfect gradation -- the earlier they were planted, the earlier they flowered and fruited. Planting by the Moon seemed to have no effect whatsoever on beans.

I therefore dismissed Moon planting for a decade, murmuring tactfully to questions at garden shows that no, I didn't follow Moon planting, I'd tested it and it didn't seem to work, usually adding with extreme cowardice "for me". Nevertheless I kept hearing impassioned declarations from Moon planting gardeners, who swore that planting by the Moon worked for them. Okay, human kind likes to create order in a complex world and all the rest of it, and neat charts that document some aspect of the natural world are comforting even when they're hogwash. Or perhaps Moon planters feel they achieve some mystic communion with the natural world by following the guidance of the Moon, a pleasing combination of spiritual one-upmanship and the ability to grow more beans than their neighbours.

More to the point, years after that first test, I discovered that there are different systems of Moon planting. One person's successful day with brassicas may be another's time to commune with carrots. But when I looked back at my initial results the peak growing times still didn't correspond to anyone's idea of the best Moon times. Nevertheless I tried my bean plantings again, this time with competing Moon charts. There was still no win for Moon planting. The results were still due to faster growth in warmer soil.

A rational explanation
And there the matter rested, until today, when I realised that there is a rational explanation for the claims of Moon planters. My moment of enlightenment was sparked by an email the night before, asking if I knew anyone who would give an interview on Moon planting. This led in turn to a stroll at dusk among this year's bean crop, where I noticed once again that the ones I'd planted later germinated before the ones I'd planted earlier based on the first warm spell.

Look at it this way. Gardener A is a Moon planter, Gardener B isn't. Both wait until spring to plant their beans because no sensible cool-climate gardener will plant beans in winter. It's too cold for them to germinate, and many seeds will rot or be taken by ants. But come the first warm spell Gardener B assumes that spring has arrived and plants his beans. Gardener A, on the other hand, waits until the next good Moon planting time before planting his beans.

Early warm spells are usually followed by a cold one, when seeds planted too early may rot. And plants that suffer set-backs when they are young rarely do as well as plants that have flourished right from the start. The set-back can be from cold, or boggy soil, or snails, or scale attack -- the effect is the same. So contrary to what we might expect, beans planted later in spring will probably do better than beans planted earlier. This applies to most other spring vegetables, of course, not just beans. The effect is slightly different for spring flowers -- early planted seeds or seedlings may bloom earlier, but the plants won't be as large and the flowering time will be shorter, with fewer and often smaller blooms. The end result is that Gardener A's Moon planted beans produce sturdier plants and crop earlier than Gardener B's beans.

The reverse may happen in autumn -- the Moon planting gardener is aware there is only one good Moon time left for planting and gets his seeds in without delay -- and in autumn, earlier planting into warmer soil usually means bigger plants. I suggest that this tendency towards slightly later spring planting and slightly earlier autumn planting explains why Moon planters swear there is an effect even though their systems are in mutual conflict. Indeed, one keen Moon planter for more than 30 years told me he finds Moon planting more effective for early rather than late spring plants, which is precisely in line with my explanation, although he himself says it's because the young spring Moon is more powerful. Conclusion: generations of gardeners may not be deluded about the efficacy of Moon planting. But the reason it works is different from the one they claim.

By the way, gardening folklore in general is often based on accurate observation. It's just that the reasoning may be faulty. For example, over the years I've tested various bits of "companion planting" folklore. And some actually work, but not because "basil likes tomatoes" (which actually doesn't work because basil planted near tomatoes tends to get black spot, while the tomatoes do neither better nor worse). Never trust a gardening book that tells you that marigolds deter aphids -- beans, onions and fuchsias planted with marigolds get more aphids, not fewer, and I suspect the same is true of other plants. On the other hand, root knot nematodes do appear to avoid the root secretions of marigolds, though a companion crop of marigolds can make the problem worse for other reasons. So remember that a gardening observation (like Moon planting) may be true even though the reasoning is faulty.

From       (1900 words 1 graphic)       Home       Fast-Find Index