Planting by the Moon - Ep. 270

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!

Planter Box Direct special is still happening! Use code JUSTGROW20 to save 20% and get free shipping at PlanterBoxDirect.com now through October 15th. Missed the deadline? You can still use JUSTGROW10 to save!!

References and transcript for this episode can be found at https://justgrowsomethingpodcast.com/episode/planting-by-the-moon-ep-270

Episode Transcript

(00:02):
It is officially spooky season and as I record this, tonight
will be a full moon. In fact, it is the Harvest Super
Moon here in the northern hemisphere.
Harvest moons are typically whenfarmers would labor under the
light of the moon to gather their crops.
Of course this was in the time before artificial light was
invented. This harvest moon coincides with

(00:24):
the moons closest approach to Earth in its 27 day orbit, which
means it will appear a little bit larger and a little bit
brighter than usual as it rises,which makes it a super moon.
And it is very possible that your online gardening group is
absolutely abuzz right now with advice that tomatoes grow better
if you plant them in the days leading up to the full moon, and

(00:48):
that your beats will be more voluptuous if you plant them
after the full moon. And all of this works better if
you're wearing your lucky gardening gloves.
OK, well, maybe not that last one, but does gardening by the
moon actually change anything inyour garden?
I have been asked about gardening by the moon's phases
so many times, so today I'll just grow something.

(01:11):
We're digging into the science why we might think the lunar
cycle can affect our garden, what has been tested and what
hasn't. 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.

(01:32):
Hey, I'm Karen, and what startedas a small backyard garden 20
years ago turned into a lifelongpassion for growing food.
Now, as a market farmer and horticulturist, I want to help
you. Do the same.
On this podcast I am your friendin the garden teaching evidence
based techniques to help you. Grow your favorites.
And build confidence in your own.
Garden space, so grab your. Garden journal and a cup of

(01:53):
coffee and get ready to just grow something.
So moon gardening has been around for centuries.
Lunar gardening calendars tell us basically when to plant our
beans versus our beets, when to harvest our onions, even when to

(02:13):
weed or when to prune to get specific results.
The idea basically assigns tasksto the different lunar phases.
So when we're in the waxing moon, so that's the period from
the new moon to the full moon, we're supposed to plant our
above ground annual crops. This is also the time when

(02:36):
mowing or pruning is done to encourage new growth.
The waning moon is that period from the full moon into the new
moon, and that is when we're supposed to sow our root crops
or transplant our plants to encourage that rooting behavior.
And the last quarter, so that's the end of that waning moon

(02:59):
phase. This is known as the waning
Crescent is when we aren't supposed to be planting
anything. We're supposed to be harvesting
and storing or fertilizing our plants.
This is also when we're supposedto be cutting or pruning our
plants to limit new growth. So if you didn't want to have to
cut your lawn as frequently, this is when you should mow the

(03:19):
lawn, right? And the logic.
Behind this is based on gravity and light.
So you know the thought behind this is that the moons gravity
affects water, meaning the tides, and so by that same logic
it should move water in the soiland in our plants.

(03:40):
And the thinking is also that the moons light hues certain
plant physiological changes. So if the moon moves oceans then
surely it nudges SAP and soil moisture.
And if plants can detect faint light then maybe a full moon
trigger something in their internal clocks.

(04:01):
OK I can see this but what does the science say?
Let's look at the physics behindmoonlight and gravity.
Moonlight itself is very dim, soa typical full moon
illuminescence near the ground level is roughly .1 to .3 lux.

(04:23):
It can occasionally be higher ifyou are in really ideal
condition. So if there's no other light
around and it's a full super moon and there's no cloud cover,
then maybe we're talking about aMax of 1 lux.
If we compare this to everyday St. lighting, everyday St.
lighting is between 10 all the way up to 100 lux if we're

(04:47):
talking about lighting that you have like on the highway.
And most of us live in areas where there is tons of this
light pollution around. So our garden plants are getting
more from that artificial like ambient light than they are from
the moon at any of its phases. So studies in astrobiology and

(05:08):
this night sky photometry shows that levels of moonlight
contribute very, very negligibleamounts to the photosynthetic
energy for most plants. The plants can perceive that
light via its light receptors, but moonlight is basically a

(05:30):
weak information signal. It is not an actual energy
source for growth. It does does not spur
photosynthesis. OK, we're talking about gravity.
The lunar gravitational variation at our garden scale is
minuscule compared to the Earth's actual gravity.

(05:52):
So we have those lunar solar tides and they're very obvious
in the oceans and even some groundwater systems.
But if we look at like Extensionand physics reviews, they
basically show that this gradient is too small to change
SAP flow or soil water availability in a way that would

(06:12):
mean that we should time our plantings around it.
The implication of this is that,you know, basically timing our
field tasks by tide, like soil moisture swings, isn't really
supported by physics. So why else might we think that
our garden plants are affected by the lunar cycle?

(06:34):
It's because of our observation of animals.
In most cases, animals don't just notice the moon, they
schedule their lives around it. Whether they realize it or not,
coyotes will chorus the loudest together during the new moon.
That is the darkest night. Some owls and Badgers shift
their routines with the phases of the moon, and probably the

(06:57):
most famous one is coral reefs. They practically throw a lunar
baby shower a few days after thefull moon.
Coral do a mass spawning a few days after we have a full moon,
and it is so large and so regular that you can actually
see it from space. So changes in behavior and in
animals and invertebrates has been studied extensively.

(07:19):
So, you know, when we see rhythms like that elsewhere in
the natural world, then it's very easy to think that, like,
our peas and our Peppers must beon that same cosmic calendar.
But moonlight's effect on plantshas usually been just
disregarded as a myth. And so of course, there hasn't

(07:41):
been a ton of research on this. The research that was done
initially was done way back in the 1920s and the 1930s, and it
did show effects on plants from moonlight exposure.
But just like everything in science, you know, we go back
and we look at this research over and over and over again as
the years go on. And as this was done, it turns

(08:04):
out that the effects that they were seeing in those studies in
plants was not due to the light itself from the Moon, but
instead it was based on what we call gravimetric oscillation.
So that is that slight tidal effect that we get daily, and
that's a result of the impact that the sun and the moon have

(08:26):
on the Earth's surface gravity. It is a tiny, tiny change, and
it changes daily. And this Luna solar tide does
seem to affect leaf movement andstem elongation and fluctuations
and things like tree stem diameter.
It's minuscule. And again, these changes occur

(08:46):
daily, but those very minor shifts in gravity are signals to
the plants to do something. And as if to further confuse the
issue, it seems that we as humans also perceive these lunar
oscillations. Researchers tracked sleep in

(09:07):
rural communities without electricity and in Seattle,
which is a big city. And it's often very cloudy,
right? And they still found this tidy
little lunar wave. People went to bed later, and
they slept less in the days leading up to a full moon,
regardless of whether they perceived that moonlight or not.

(09:31):
These results were repeated overand over again, even where
streetlights outshine the moonlight by a lot.
So if our own circadian rhythm can catch that tiny little
gravitational shift, then it's tempting to assume that our
lettuce seeds might catch that shift too.

(09:51):
And we did say that plants can perceive light no matter how
weak it is. It is possible that these lunar
signals do affect some plants insome way other than
photosynthesis. There have been a number of
studies recently that looked at very specific plants, so coffee,
mustard, tobacco and legumes. And what they found in these

(10:14):
separate studies was that full moonlight prompted changes in
gene activity literally overnight in some plants.
But it can enhance post germination growth rates in some
species. And it could possibly have long
term developmental effects from even just that short term

(10:35):
moonlight exposure. And even low moonlight levels
can have a slight impact on leafmovements and the timing of
flowering. So this is kind of a plot twist,
right? Coffee leaves will flip like
genetic switches based on a fullmoon.
Mustard seedlings get a little bit of a growth nudge after a

(10:55):
few nights of moonlight. So yes, plants can perceive
moonlight as a signal. The $1,000,000 question here is
whether that signal is strong enough and reliable enough that
we should schedule our planting activities around it.
Remember, these studies are species specific and they are

(11:16):
often short term, and they were done in controlled conditions or
in very carefully timed field samplings.
But they do show that there is an effect on plants from both a
gravitational and a light standpoint, even if it's
minuscule. So there are some arguments for
planting by the moon because younever know how it might affect
your garden, right? Well, coming up, the naysayers

(11:40):
weigh in. We will look at the studies
against planting by the moon. That's next.
OK, So what about evidence against practical moon phase
planting calendars? If we look at university and
extension reviews of all of the different studies that have been
done, these reviews find no consistent replicated field

(12:05):
evidence that sowing or transplanting by lunar phase
improves germination yield or quality.
And we have to think about this from a university extension
standpoint. These researchers and scientists
are essentially trying to get these improvements in

(12:25):
germination and yield and quality for farmers, right?
We're looking at large planting operations, thousands of acres
at a time of corn and wheat and soy and all of those types of
things. So if there if there was any
evidence whatsoever that planting by the phases of the
moon could give us some consistently replicable

(12:48):
increases in any of those things, they would absolutely be
recommending this to farmers. And that simply just is not
happening. So if they're not recommending
it on a large scale, they likelyaren't going to be recommending
it for us on a smaller scale. In fact, there was a 2020 review
in the Journal of Agronomy, if Iremember correctly, and it was

(13:11):
assessing both the physics and the biology of this whole
phenomenon. And basically what they found
was, yes, there are lunar influences that do exist in
nature, but there weren't any really robust agricultural
benefits tied to lunar calendarsbased on the current evidence.

(13:35):
And those studies that showed changes in the plants based on
lunar solar cycles did not demonstrate improved field
yields or germination rates or even the storage quality in a
way that we as gardeners who likely, you know, grow in areas
where extra light from outside sources is stronger than what

(13:57):
that we get from moonlight. Right.
And a lot of the times when we see these anecdotal results
around lunar planting, it is likely mixed up with legitimate
circadian and seasonal plant rhythms.
And I know the classic claim is,well, we're mostly water and so
are plants, so the moon should tug on our fluids just like the

(14:20):
tides. But the moon's pull on our body
is so weak that the gravitational pull of a large
building when we're standing next to it is stronger than what
the moon does. OK.
And the same thing goes for our plants.
Tides need large, very mobile water sources to happen.

(14:42):
And in plants, the water is mostly locked in their cells and
in the Xylem. It's moved by transpiration and
by pressure gradients. It's not moved by lunar gravity.
So we have intriguing lab results, but when universities
and research reviewers ask the really tough question, do lunar

(15:03):
calendars improve real world outcomes, the answer so far is
no. There is no consistent
advantage. Weather and the soil,
temperatures and our day length consistently drown out the
moon's signal. And yet, despite evidence to the

(15:23):
contrary, people will still swear by lunar gardening.
Why? Well, that happens with a lot of
things. For example, surveys will show
you that many dark doctors and nurses believe that the full
moon means more patients and a wild night in the ER.
But very well run studies and reviews of all of the patient

(15:48):
data will show that ER admissions and trauma severity
does not increase around a full moon.
But I personally know ER nurses who's aware that the full moon
brings out the crazies. Okay, gardening folklore can
work in the same way. Very memorable nights and bumper
harvests are going to stick in our heads.

(16:11):
But the nights and the so so harvests, well, they're going to
tend to fade from memory. Belief persists even when the
data says otherwise. So the bottom line is this
moonlight can be an environmental cue that plants
detect. There is no strong replicated

(16:34):
field evidence that timing our tasks by lunar phases beats
proven scheduling by soil temperature and frost dates and
day length, or our particular weather windows.
Now, if moon phase timing motivates you to like, plan and
observe your garden more carefully, then by all means go
for it. But let's prioritize timing our

(16:58):
planting and our pruning and ourharvesting activities based on
1st, the soil temperature and the moisture availability, then
by our local frost or freeze probabilities and our day
length, then by our weather windows, so rain and wind and
any heat spikes or cold temperatures, right.
Then by our pest and disease pressure.

(17:19):
So planting or planning our planting activities around the
activities of like or the reproductive schedule of your
most determined pest. Then by variety or maturity and
photo period sensitivity. This is especially important
when we're talking about things like onions, right?
It makes no sense to plant a bulb onion by the particular

(17:43):
lunar cycle if we're not planting the correct type of
onion for our area and we're notplanting it at the right time of
the year for it to form that bulb during the particular day
length that it needs, right? These are all things that are
really, really important before we get to planting by the lunar
phase. By all means, if all of these

(18:05):
other things line up in your calendar and then you can shift
that calendar a little bit to plant by the lunar phase as an
experimental sort of overlay to everything, then go for it.
But I would consider this last thing to be completely optional.
So your storage quality of all of your produce is going to
click. Correlate far more with maturity

(18:26):
and the curing conditions of ourharvest than with the lunar
phase. Seed germination is driven by
soil moisture and temperature, and that individual seed coats
permeability. There is no solid field evidence
that says that lunar gravity changes the soil water at seed
depth enough to even matter, andextremely low moonlight can

(18:52):
tweak photoreceptors in some plant species, but streetlights
and porch lights are a much bigger factor in our gardens.
As with everything in gardening,it's your garden and it's your
time, so do what feels right to you.
Just remember to track everything in your garden
journal so you can see the real results for yourself.

(19:15):
Until next time, my gardening friends, keep on cultivating
that dream garden, and we'll talk again soon.