As I record this, tonight will be a full moon. In fact, it’s the Harvest Supermoon here in the northern hemisphere. And it’s very possible that your online gardening group is absolutely abuzz with advice that tomatoes grow better if you plant them in the days leading up to the full moon and your beets grow more voluptuous if you plant them after the full moon.
But does gardening by the moon actually change anything in your garden? I have been asked about gardening by the moon’s phases so many times, so today on Just Grow Something we’re digging into the science—why we think the lunar cycle can affect our garden, what’s been tested, and what hasn’t. And at the end you can decide whether you want to modify your planting calendar next season to include the phases of the moon. Let’s dig in!
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References and transcript for this episode can be found at https://justgrowsomethingpodcast.com/episode/planting-by-the-moon-ep-270
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It is officially spooky season and as I record this, tonight
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will be a full moon. In fact, it is the Harvest Super
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Moon here in the northern hemisphere.
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Harvest moons are typically when farmers would labor under the
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light of the moon to gather their crops.
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Of course this was in the time before artificial light was
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invented. This harvest moon coincides with
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the moons closest approach to Earth in its 27 day orbit, which
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means it will appear a little bit larger and a little bit
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brighter than usual as it rises, which makes it a super moon.
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And it is very possible that your online gardening group is
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absolutely abuzz right now with advice that tomatoes grow better
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if you plant them in the days leading up to the full moon, and
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that your beats will be more voluptuous if you plant them
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after the full moon. And all of this works better if
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you're wearing your lucky gardening gloves.
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OK, well, maybe not that last one, but does gardening by the
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moon actually change anything in your garden?
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I have been asked about gardening by the moon's phases
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so many times, so today I'll just grow something.
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We're digging into the science why we might think the lunar
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cycle can affect our garden, what has been tested and what
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hasn't. At the end, you can decide
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whether you want to modify your planting calendar next season to
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include the phases of the moon. Let's dig in.
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Hey, I'm Karen, and what started as a small backyard garden 20
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years ago turned into a lifelong passion for growing food.
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Now, as a market farmer and horticulturist, I want to help
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you. Do the same.
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On this podcast I am your friend in the garden teaching evidence
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based techniques to help you. Grow your favorites.
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And build confidence in your own.
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Garden space, so grab your. Garden journal and a cup of
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coffee and get ready to just grow something.
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So moon gardening has been around for centuries.
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Lunar gardening calendars tell us basically when to plant our
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beans versus our beets, when to harvest our onions, even when to
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weed or when to prune to get specific results.
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The idea basically assigns tasks to the different lunar phases.
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So when we're in the waxing moon, so that's the period from
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the new moon to the full moon, we're supposed to plant our
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above ground annual crops. This is also the time when
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mowing or pruning is done to encourage new growth.
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The waning moon is that period from the full moon into the new
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moon, and that is when we're supposed to sow our root crops
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or transplant our plants to encourage that rooting behavior.
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And the last quarter, so that's the end of that waning moon
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phase. This is known as the waning
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Crescent is when we aren't supposed to be planting
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anything. We're supposed to be harvesting
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and storing or fertilizing our plants.
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This is also when we're supposed to be cutting or pruning our
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plants to limit new growth. So if you didn't want to have to
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cut your lawn as frequently, this is when you should mow the
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lawn, right? And the logic.
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Behind this is based on gravity and light.
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So you know the thought behind this is that the moons gravity
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affects water, meaning the tides, and so by that same logic
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it should move water in the soil and in our plants.
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And the thinking is also that the moons light hues certain
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plant physiological changes. So if the moon moves oceans then
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surely it nudges SAP and soil moisture.
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And if plants can detect faint light then maybe a full moon
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trigger something in their internal clocks.
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OK I can see this but what does the science say?
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Let's look at the physics behind moonlight and gravity.
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Moonlight itself is very dim, so a typical full moon
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illuminescence near the ground level is roughly .1 to .3 lux.
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It can occasionally be higher if you are in really ideal
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condition. So if there's no other light
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around and it's a full super moon and there's no cloud cover,
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then maybe we're talking about a Max of 1 lux.
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If we compare this to everyday St. lighting, everyday St.
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lighting is between 10 all the way up to 100 lux if we're
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talking about lighting that you have like on the highway.
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And most of us live in areas where there is tons of this
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light pollution around. So our garden plants are getting
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more from that artificial like ambient light than they are from
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the moon at any of its phases. So studies in astrobiology and
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this night sky photometry shows that levels of moonlight
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contribute very, very negligible amounts to the photosynthetic
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energy for most plants. The plants can perceive that
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light via its light receptors, but moonlight is basically a
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weak information signal. It is not an actual energy
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source for growth. It does does not spur
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photosynthesis. OK, we're talking about gravity.
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The lunar gravitational variation at our garden scale is
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minuscule compared to the Earth's actual gravity.
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So we have those lunar solar tides and they're very obvious
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in the oceans and even some groundwater systems.
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But if we look at like Extension and physics reviews, they
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basically show that this gradient is too small to change
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SAP flow or soil water availability in a way that would
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mean that we should time our plantings around it.
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The implication of this is that, you know, basically timing our
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field tasks by tide, like soil moisture swings, isn't really
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supported by physics. So why else might we think that
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our garden plants are affected by the lunar cycle?
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It's because of our observation of animals.
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In most cases, animals don't just notice the moon, they
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schedule their lives around it. Whether they realize it or not,
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coyotes will chorus the loudest together during the new moon.
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That is the darkest night. Some owls and Badgers shift
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their routines with the phases of the moon, and probably the
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most famous one is coral reefs. They practically throw a lunar
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baby shower a few days after the full moon.
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Coral do a mass spawning a few days after we have a full moon,
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and it is so large and so regular that you can actually
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see it from space. So changes in behavior and in
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animals and invertebrates has been studied extensively.
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So, you know, when we see rhythms like that elsewhere in
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the natural world, then it's very easy to think that, like,
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our peas and our Peppers must be on that same cosmic calendar.
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But moonlight's effect on plants has usually been just
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disregarded as a myth. And so of course, there hasn't
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been a ton of research on this. The research that was done
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initially was done way back in the 1920s and the 1930s, and it
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did show effects on plants from moonlight exposure.
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But just like everything in science, you know, we go back
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and we look at this research over and over and over again as
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the years go on. And as this was done, it turns
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out that the effects that they were seeing in those studies in
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plants was not due to the light itself from the Moon, but
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instead it was based on what we call gravimetric oscillation.
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So that is that slight tidal effect that we get daily, and
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that's a result of the impact that the sun and the moon have
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on the Earth's surface gravity. It is a tiny, tiny change, and
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it changes daily. And this Luna solar tide does
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seem to affect leaf movement and stem elongation and fluctuations
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and things like tree stem diameter.
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It's minuscule. And again, these changes occur
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daily, but those very minor shifts in gravity are signals to
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the plants to do something. And as if to further confuse the
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issue, it seems that we as humans also perceive these lunar
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oscillations. Researchers tracked sleep in
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rural communities without electricity and in Seattle,
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which is a big city. And it's often very cloudy,
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right? And they still found this tidy
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little lunar wave. People went to bed later, and
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they slept less in the days leading up to a full moon,
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regardless of whether they perceived that moonlight or not.
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These results were repeated over and over again, even where
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streetlights outshine the moonlight by a lot.
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So if our own circadian rhythm can catch that tiny little
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gravitational shift, then it's tempting to assume that our
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lettuce seeds might catch that shift too.
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And we did say that plants can perceive light no matter how
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weak it is. It is possible that these lunar
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signals do affect some plants in some way other than
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photosynthesis. There have been a number of
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studies recently that looked at very specific plants, so coffee,
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mustard, tobacco and legumes. And what they found in these
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separate studies was that full moonlight prompted changes in
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gene activity literally overnight in some plants.
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But it can enhance post germination growth rates in some
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species. And it could possibly have long
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term developmental effects from even just that short term
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moonlight exposure. And even low moonlight levels
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can have a slight impact on leaf movements and the timing of
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flowering. So this is kind of a plot twist,
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right? Coffee leaves will flip like
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genetic switches based on a full moon.
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Mustard seedlings get a little bit of a growth nudge after a
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few nights of moonlight. So yes, plants can perceive
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moonlight as a signal. The $1 question here is
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whether that signal is strong enough and reliable enough that
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we should schedule our planting activities around it.
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Remember, these studies are species specific and they are
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often short term, and they were done in controlled conditions or
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in very carefully timed field samplings.
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But they do show that there is an effect on plants from both a
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gravitational and a light standpoint, even if it's
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minuscule. So there are some arguments for
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planting by the moon because you never know how it might affect
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your garden, right? Well, coming up, the naysayers
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weigh in. We will look at the studies
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against planting by the moon. That's next.
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OK, So what about evidence against practical moon phase
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planting calendars? If we look at university and
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extension reviews of all of the different studies that have been
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done, these reviews find no consistent replicated field
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evidence that sowing or transplanting by lunar phase
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improves germination yield or quality.
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And we have to think about this from a university extension
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standpoint. These researchers and scientists
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are essentially trying to get these improvements in
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germination and yield and quality for farmers, right?
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We're looking at large planting operations, thousands of acres
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at a time of corn and wheat and soy and all of those types of
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things. So if there if there was any
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evidence whatsoever that planting by the phases of the
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moon could give us some consistently replicable
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increases in any of those things, they would absolutely be
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recommending this to farmers. And that simply just is not
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happening. So if they're not recommending
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it on a large scale, they likely aren't going to be recommending
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it for us on a smaller scale. In fact, there was a 2020 review
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in the Journal of Agronomy, if I remember correctly, and it was
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assessing both the physics and the biology of this whole
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phenomenon. And basically what they found
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was, yes, there are lunar influences that do exist in
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nature, but there weren't any really robust agricultural
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benefits tied to lunar calendars based on the current evidence.
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And those studies that showed changes in the plants based on
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lunar solar cycles did not demonstrate improved field
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yields or germination rates or even the storage quality in a
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way that we as gardeners who likely, you know, grow in areas
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where extra light from outside sources is stronger than what
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that we get from moonlight. Right.
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And a lot of the times when we see these anecdotal results
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around lunar planting, it is likely mixed up with legitimate
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circadian and seasonal plant rhythms.
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And I know the classic claim is, well, we're mostly water and so
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are plants, so the moon should tug on our fluids just like the
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tides. But the moon's pull on our body
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is so weak that the gravitational pull of a large
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building when we're standing next to it is stronger than what
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the moon does. OK.
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And the same thing goes for our plants.
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Tides need large, very mobile water sources to happen.
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And in plants, the water is mostly locked in their cells and
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in the Xylem. It's moved by transpiration and
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by pressure gradients. It's not moved by lunar gravity.
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So we have intriguing lab results, but when universities
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and research reviewers ask the really tough question, do lunar
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calendars improve real world outcomes, the answer so far is
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no. There is no consistent
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advantage. Weather and the soil,
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temperatures and our day length consistently drown out the
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moon's signal. And yet, despite evidence to the
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contrary, people will still swear by lunar gardening.
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Why? Well, that happens with a lot of
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things. For example, surveys will show
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you that many dark doctors and nurses believe that the full
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moon means more patients and a wild night in the ER.
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But very well run studies and reviews of all of the patient
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data will show that ER admissions and trauma severity
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does not increase around a full moon.
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But I personally know ER nurses who's aware that the full moon
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brings out the crazies. Okay, gardening folklore can
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work in the same way. Very memorable nights and bumper
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harvests are going to stick in our heads.
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But the nights and the so so harvests, well, they're going to
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tend to fade from memory. Belief persists even when the
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data says otherwise. So the bottom line is this
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moonlight can be an environmental cue that plants
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detect. There is no strong replicated
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field evidence that timing our tasks by lunar phases beats
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proven scheduling by soil temperature and frost dates and
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day length, or our particular weather windows.
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Now, if moon phase timing motivates you to like, plan and
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observe your garden more carefully, then by all means go
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for it. But let's prioritize timing our
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planting and our pruning and our harvesting activities based on
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1st, the soil temperature and the moisture availability, then
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by our local frost or freeze probabilities and our day
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length, then by our weather windows, so rain and wind and
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any heat spikes or cold temperatures, right.
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Then by our pest and disease pressure.
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So planting or planning our planting activities around the
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activities of like or the reproductive schedule of your
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most determined pest. Then by variety or maturity and
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photo period sensitivity. This is especially important
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when we're talking about things like onions, right?
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It makes no sense to plant a bulb onion by the particular
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lunar cycle if we're not planting the correct type of
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onion for our area and we're not planting it at the right time of
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the year for it to form that bulb during the particular day
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length that it needs, right? These are all things that are
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really, really important before we get to planting by the lunar
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phase. By all means, if all of these
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other things line up in your calendar and then you can shift
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that calendar a little bit to plant by the lunar phase as an
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experimental sort of overlay to everything, then go for it.
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But I would consider this last thing to be completely optional.
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So your storage quality of all of your produce is going to
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click. Correlate far more with maturity
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and the curing conditions of our harvest than with the lunar
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phase. Seed germination is driven by
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soil moisture and temperature, and that individual seed coats
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permeability. There is no solid field evidence
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that says that lunar gravity changes the soil water at seed
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depth enough to even matter, and extremely low moonlight can
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tweak photoreceptors in some plant species, but streetlights
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and porch lights are a much bigger factor in our gardens.
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As with everything in gardening, it's your garden and it's your
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time, so do what feels right to you.
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Just remember to track everything in your garden
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journal so you can see the real results for yourself.
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Until next time, my gardening friends, keep on cultivating
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that dream garden, and we'll talk again soon.