Science Update: Moonlight

A deeper look into the influence of our natural satellite

Life on earth would be quite different without our natural satellite. The daily rising and falling of the moon, along with the monthly waxing and waning cycles, have effects on our oceans and seas. The tides are crucial to life: tidal pools, sheltered and renewed in rhythm with these cycles, catalyzed some of the first stable ecologies and still represent unique niches. While it may not be as widely recognized yet, it is becoming more clear that the moon also affects the flow of water through plants: sap moves more vigorously during the waxing phase as the moon grows to full, and slows down as the moon wanes to a thin morning crescent.

Isabella Guerrini, at the University of Perugia in Italy and a lecturer at the Findhorn Foundation and Park (close to Inverness, Scotland), works in the department of agriculture studying plant and animal consciousness and its integration into ecological pattern and rhythm. Her observations of sap flow in plants suggest1 that, indeed, fluid flows more full as the moon becomes full, and slows down as the moon wanes. This, she explains, has important consequences for plant growth and pruning: vigorous, sappy plants will suffer if cut, harvested, or pruned close to the full moon. First off, leaking sap exposes the plant to disease and pest incursion. But furthermore, sap from a cut plant, now deprived of its primary outlet, will engorge smaller channels, where new buds are developing on side branches, and potentially rupture those channels leading to the death of the buds (a phenomenon known as “lunar burn”, because it was so often noted around the full moon). Less vigorous, less juicy plants, like ground-covers or vines, conversely may benefit from being cut when sap flow is strong: it will stimulate the development of side shoots and encourage fuller, branching growth.

Those who work with plants every day have certainly noticed differences in moisture content, flavor (often a stand-in for some of the plant’s chemistry), and more. This can have important consequences across a range of applications, from herbal medicine to construction. For an excellent review of the subject, see Ian Cole and Michael Balick’s review article.2 The authors discuss a range of traditional practices related to moon phase, from the harvesting of construction and thatch materials, to the planting of staple crops, to the gathering of medicinal herbs. In their review of some contemporary research, they catalog differences in plant chemistry and fluid balance based on seasonal and circadian (day-long) rhythms, but note that studies that examine lunar rhythms are still few and far between. In my personal experimentation, I concur that flavor and phytochemical variation is most noticeable as part of a seasonal cycle, but moisture content is somewhat tied to lunar cycles. Based on my own simple observations weighing a plant sample before and after drying, water weight can vary up to 10% between the days just before and after the full moon, and the week before the new moon. This parallels what researchers have found in lumber: wood from spruce and chestnut, harvested in the last week of the moon phase, has the lowest water percentage and shrinks the least during drying.3 It is rumored that the wooden stilts upon which Venice was built all were harvested during the last few days of the moon cycle: less water and denser fibers means less susceptibility to rotting and parasites.

Ernst Zürcher, who published the research on lumber harvesting, expanded on Cole and Balick’s work,4 cataloging the changes in moisture content, as well as effects on plant germination, growth, and development in many different plants as relates to lunar cycles. The conclusions are consistent: there is indeed a lunar effect. But he also points out that the easy explanation (a tide-like gravitational force) is most likely incorrect, as the amount of water in even the largest tree is relatively small, and a tidal force would be negligible. An intriguing, though as of yet unconfirmed hypothesis is that moonlight itself may contribute to electromagnetic changes in certain plants, altering the surface tension of water and allowing for some of the microscopic effects that have been experimentally documented. All plants grow differently during different phases of the moon--this has been observed in scientific research since the 1970s5 and, more recently, documented on the microscopic level by observing changes in rootlet growth.6 But as to why--this question is still unresolved.


In conclusion, moonlight is subtle--typically, even at its peak, only about 15% as strong as sunlight. But its rays penetrate the soil somewhat, and may affect plant life from germination to harvest. Most plants seem to need a rhythmic exposure to moonlight--at least for a week or so around the full moon--for optimal immunity, wound healing, regeneration, and growth. Plant harvesting should ideally heed the lunar cycle, not simply for potency and low water content, but because many plants (especially strong, vigorous growers) recover better when they are harvested during the last week of the lunar cycle. Modern research is confirming many of the observations recorded in the oral tradition of farmers, foresters, and herbalists, but is just beginning to explain why. It seems that the subtle effects of moonlight can alter the way water behaves as it interfaces with living cells, perhaps through bio-electric mechanisms. As the old myths tell us, the moon is a powerful force, regulating the unseen, yin-like processes hidden under the surfaces of things, deeply connected to water and moisture. Simple explanations of its effects can often be misdirection--the moon may seem to lay out a trail for us, but this trail often leads to places we’d never expect. But just as tidal forces served to shape early life on our planet, the more hidden effects we are just starting to understand may be essential to maintain healthy life on earth today. What we do know is that moonlight, while generally similar to the sunlight it reflects, shifts a bit towards the infrared (see spectral graph, from CIRA, at Colorado State University) and also has some gaps that may be linked to the presence of traces of sodium in the lunar “atmosphere."7 This makes moonlight not just a less intense version of sunlight--it is somewhat qualitatively different, too. Dr. Guerrini has speculated that the rhythmic, additional irradiation from moonlight is an important adjunct to the growth and metabolism of healthy plants: not only have we seen change in growth and leaf movements, but also in patterns of starch storage (highest in the waning phase) and utilization (highest in the days before the full moon). These effects, along with preliminary documentation of immune deficiency and poor wound healing from moonlight-deprived plants, encourage us to think of moonlight as an important part of a plant’s overall “nutrition”. Interestingly, this “nutrition”8 seems to be more a modulation of bio-electric activity in the plant rather than a source of photosynthetic energy.

  1. Recorded in Enigmi e simboli nelle piante e nei giardini [Mysteries and symbols in plants and gardens], ed. Paola Maresca, Angelo Pontecorboli pub., Florence, 2012
  2. Cole, Ian B., and Michael J. Balick. "Lunar Influence: Understanding Chemical Variation and Seasonal Impacts on Botanicals." American Botanical Council. HerbalGram 85 (2010): 50-56.
  3. Zürcher, Ernst, et al. "Looking for differences in wood properties as a function of the felling date: lunar phase-correlated variations in the drying behavior of Norway Spruce (Picea abies Karst.) and Sweet Chestnut (Castanea sativa Mill.)." Trees 24.1 (2010): 31-41.
  4. Zürcher, Ernst. "Plants and the Moon-Traditions and Phenomena." American Botanical Council–HerbalEGram 8.4 (2011).
  5. Abrami, Giovanni. "Correlations between lunar phases and rhythmicities in plant growth under field conditions." Canadian Journal of Botany 50.11 (1972): 2157-2166.
  6. Barlow, Peter W., and Joachim Fisahn. "Lunisolar tidal force and the growth of plant roots, and some other of its effects on plant movements." Annals of botany 110.2 (2012): 301-318.
  7. Colaprete, A., et al. "How surface composition and meteoroid impacts mediate sodium and potassium in the lunar exosphere." Science (2015): aad2380.
  8. Barlow, Peter W. "Moon and cosmos: plant growth and plant bioelectricity." Plant Electrophysiology. Springer Berlin Heidelberg, 2012. 249-280.

 Updated August 2021

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