Moon Planting philosophy is a Myth in that it does not work for the reason Lunar Planters think it does, but there are several reasons why people swear by it.
How They Think It Works
There are two main ideas behind moon gardening practices. First, lunar gardeners believe the moon's gravitational pull affects the flow of moisture in the soil. Just as the moon has a noticeable effect on the oceans in the tides, the moon may have a subtler effect on smaller bodies of water and thus change the levels of water in the soil. For example, to take advantage of the lunar cycle, a gardener would avoid turning over the soil in his or her garden when there is the most moisture in it (and thus when the soil was hardest to turn over) which lunar gardeners propose is during the new and full moons. Another, less direct, proposed connection between the moon and gardening is that moonlight is thought to have an effect on seed germination because exposure to light can enhance germination. [Ref]
What's Going On
Let’s look at a possible scenario.
Gardener I is a moon planter; Gardener
II isn’t. Both gardeners wait till
spring to plant their beans. (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
II succumbs to one of the great
spring urges and plants the beans at
the first hint that spring has arrived.
Gardener I, on the other hand, waits
till the next good moon planting time
before planting the seeds.
Early warm spells are usually
followed by another cold one… and
again seed planted too early may rot.
Even if it doesn’t, plants that suffer
any set-back when they are young
usually don’t do as well as plants
that have flourished right from the
start. (The set-back can be from cold,
boggy soil, snail or scale attack —
the effect is the same). So counterintuitively,
beans that are planted
later in spring will probably do better
than beans planted too early. [Ref]
The result is essentially that what may seem as an intuitively good time to do gardening is often counter-productive, and anyone adhering to a fixed schedule independent of the weather is likely to do better than the intuitive gardener.
The reverse may happen in autumn
— the moon planting gardener will
be aware that they only have one
good time to plant, so may get their
seeds in without delay — and in
autumn, earlier planting into
warmer soil usually means bigger
It’s this tendency to slightly later
spring planting and perhaps slightly
earlier autumn planting, that I suspect
is the reason so many gardeners
will swear that they see an effect.
(One keen gardener who has been
following moon planting for more
than 30 years once told me that he
finds moon planting more effective
for early rather than late spring
plants, though he believes it’s because
the young spring moon is more
Which means that generations of
gardeners may not be deluded about
the efficacy of moon planting. It just
works for a different reason than the
one they believed.
Furthermore, those enjoying the superior goods of moon planters are likely to find them better for reasons other than moon planting. Confirmation Bias likely plays a role, but even more than that - someone who is attentive enough to their garden to adhere to moon planting folklore is likely to be doing other things to ensure the health of their crops - such as using healthy soil, watering properly, and being generally more attentive. In short, most of the gardening behaviour that goes hand in hand with the superstitious tendencies will have an actual positive effect on the crop.
From this national geographic article Michael Jawson, US Department of Agriculture Systems Laboratory in Beltsville, Maryland said:
The reported benefits of moon-gardening practices are most likely indirect effects that stem from gardener’s attentive care. The indirect effect could be one simply of overall better management because of being careful to do good practices at more optimum times in relation to plant growth cycles.
Few studies have been done to test the veracity of lunar gardening. This due in large part to the fact that such experiments would need to be performed over multiple years, since weather, time of year and other external factors immediately affect plant growth. The few studies that have been done have questionable methods, limited time frame, inconclusive results or conflicting results. [Ref]
There was a study done by the Agricultural Research Service in Iowa where they found a link between weed germination and exposure to light. They determined that tilling the soil (i.e. bringing weeds to the surface) was best done at night by a new moon (when there was as little light as possible). Tilling in the dark led to less weed seed germination and thus to fewer weeds in the garden.
Pubmed - Lowell W. Woodstock and Don F. Grabe. Relationships Between Seed Respiration During Imbibition and Subsequent Seedling Growth in Zea mays L., Plant Physiol. 1967
This would suggest that freshly tilled gardens exposed to the outdoors are less likely to become weedy when it's dark out (obscured moon or cloudy weather), and facilitate false attribution of the outcome to astrological myths.
Biodynamic - Nicholas Kollerstrom and Gerhard Staudenmaier. Lunar-Sidereal Rhythms in Crop Yield, Biological Agriculture and Horticulture, 2001
This article summarizes a large number of older studies, many of which appear to support planting by the moon or other astrological principles. Invariably, the studies are near sighted, providing only a single (anecdotal) data point in time, mistakenly claiming statistical significance due to a large number of sample germinations. Studies that confirm the behaviour fail to account for the majority of independent variables which are known or theorized to affect germination and growth.
In the 1990s, discussions in print of the biodynamic calendar in Europe,
America and New Zealand, have alluded to the experiments conducted by
Spiess as having tested the Thunhypothesis and failed to replicate it (e.g., N.Z.
Biodynamic Association, 1989; Llewellyn, 1993). Enjoying widespread
publicity, and published by the Forschungsring of the German biodynamic
movement, the Spiess results have worked to discredit biodynamic calendars.
An attempt at a conclusion
So to answer your question precisely, I would say that yes, there is plenty of evidence to support the benefits of lunar planting - but this evidence is often attributed to confirmation bias, improperly conducted experiments, and a failure to account for uncontrolled variables affecting the entire test population. We have yet to produce a long term scientific study which supports lunar planting.
Basically, the time at which you plant something certainly does play a factor in how well it grows, but the thing that makes that time better or worse is not the moon.
What is much easier, is the task of dismissing the proposed mechanisms behind lunar planting. The suggestions that astrological alignment of the moon and constellations, or that lunar gravity impacts the moisture of soil, can be easily dismissed with grassroots skepticism and a basic understanding of physics.